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Beneath Our Feet

Cast in clay

By Max Helmberger, graduate student, New York State Agricultural Experiment Station, Geneva, New York, USA

 

Growing up an only child on a dirt road in the Northern Minnesota woods, I spent a lot of time outside, overturning the many thousands of glacier-strewn rocks around my house (at least the ones small enough to move) and gazing in awe at the centipedes, isopods, and invasive European earthworms underneath (which were promptly relocated to our compost bin). My first interest in soil in an academic context came the year after I graduated from high school, when I took a soil science course at my local community college. That class instilled in me a firm conviction that soil is humankind's most important natural resource, and clued me in to the fact that, in soil, there's far more than meets the eye.

After transferring to the University of Minnesota in Duluth to major in Biology, I took an entomology class and worked as a research assistant in an aboveground plant-insect ecology lab. I had always loved insects, arthropods, and invertebrates in general, and I greatly enjoyed the coursework and research experience, but wanted to connect it with my love of soil. I started searching Google Scholar for “soil arthropods”, and a few dozen soil ecology articles later, I was hooked, and I eventually sought and out and accepted a M.S. position in the lab of Dr. Kyle Wickings at the New York State Agricultural Experiment Station, a satellite campus of Cornell University located in Geneva, New York. What I didn't know as I was reading all those papers, was that I would end up reporting all the knowledge I gained from them in a most unusual way.

Clay animation, for those unaware, is a form of stop-motion animation in which clay models are photographed, moved slightly, photographed again, and so on. The pictures are strung together and played in rapid succession to give the appearance of movement. Wallace and Gromit is arguably the most famous example of the medium. When I was 7 years old, my grandmother took me to an hour-long class in clay animation. I made a video of an anthropomorphic flower dancing to some sort of classical music riff. The VHS tape is certainly hiding somewhere in my house. Fast forward to my undergraduate entomology class, and I drew on those old memories for the course's final project to make a clay animation video on the life cycle of the gallmaking fly Eurosta solidaginis, the main study organism of my research advisors’ laboratory. The video was crude by my current standards, but got me a good grade in the class nevertheless.

At Cornell, where I'm currently working on my M.S. in Entomology, I’ve had the opportunity to draw from a unique funding source called the Extension/Outreach assistantship. Instead of working off a grant or being a teaching assistant (something difficult to do when based at a satellite research campus rather than the main university campus), I earned my stipend via progress on a variety of extension and outreach projects of my advisor's and my own devising. When applying for the assistantship and listing my project objectives, my advisor and some of the faculty members on the Extension/Outreach assistantship committee were skeptical until they saw the E. solidaginis video as a proof-of-concept, and in Spring semester of 2017, I was off to the races. To avoid some of the mistakes I made with my previous clay animation, I was very careful with how I went about planning and "filming" the videos. I wrote out all of my narration in advance as well a clear script of what specific actions I would portray. Then, I timed myself reciting the narration for each scene, and so could know in advance how many frames of animation I needed. This, combined with a nice DSLR camera as a Hanukkah present from my parents, would allow for much more cohesive and polished videos than my tale of the gallmaking fly. In the end, I produced three videos, Life Cycle of Entomopathogenic Nematodes, The Soil Food Web, and Ecosystem Services in Agriculture (though the latter includes some functions performed by aboveground organisms). My funding next semester will be from the same Extension/Outreach assistantship, so I plan to produce at least one more video in addition to my other projects, possibly two. From start to finish (writing the script, creating the models, creating the set, taking the photographs, editing the video, and recording the narration), each video took me between 15 and 20 hours to make. Each video consists of 350-400 individual images, with some being repeated here and there. They’ve been received well in the department, and the entomopathogenic nematode video has even been incorporated into several extension talks. The rest of the videos have ben showcased in a few classroom settings, and I am hoping to further expand their reach. I plan to make at least two additional videos in the fall, as I will again be funded through an Extension/Outreach assistantship.

My ultimate goal is that these videos provide an accessible way of communicating soil ecology and biodiversity to lay audiences, especially young ones. Despite being the prototypical "science nerd" growing up, and being an avid consumer of books, documentaries, and Web resources about the natural world, many of the soil animals I read about during my first forays into the primary literature were completely unknown to me. I had no idea there were mites beyond dust mites and the various parasitic taxa, and certainly didn't know there were any mites as cute as a galumnid oribatid. I had never even heard of diplurans, symphylans, pauropods, and some of the other more obscure soil organisms. I knew what a pseudoscorpion was, but didn’t know I could find them in the peat bog less than a mile from my house. And that rubbed me the wrong way. It's hard for young people to learn about the marvels of soil biodiversity, especially on their own. I know that 7 year-old Max would have gotten much more out of these videos than from one about a dancing flower, and he would have started playing around with Tullgren funnels much earlier than junior year of college. As such, if you enjoy my videos, I encourage you to share them however and wherever you like. They are available online as a YouTube playlist.

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Digging deeper in urban ecology: the urban ecosystem convergence hypothesis

By Dietrich Epp Schmidt, Graduate Reserach Assistant, University of Maryland

“Even the mightiest of us return to dust, they say. Nothing remains but these shattered fragments of their kingdom… But that's not really the point, is it? These shattered fragments remain- that's the point. We look upon the magnificent temples and stelae and ball courts of Caracol in awe. There's no despair here. The Maya built something astounding and permanent. Look on our works, ye mighty, and revere. The ancient Maya speak to the twenty-first century through those temples and say: We did something amazing here.

What will our descendants think when they come upon Chalillo [dam]? When they scrape away the deep layer of dirt covering its stepping-stone facade, what will they make of the dogleg design, the Chinese gauges, the long-stopped turbines? What will they make of the skeletons and fossils of birds long gone? Will they connect the two?"

 

-Bruce Barcott, The last flight of the Scarlet Macaw

 

For a very long time, humans have experienced the world as having two fundamental domains: that which we understand as being under human control, and that which is not. Canonically, we call the latter “natural” and the former “unnatural;” and while the broader society may perceive there to be a distinction between the two, we know that our existence has an impact on ecological process, and vice versa. Our social processes, which are as basic to us as defining our identity and competing for status within our community, are intricately linked to our individual and global consumption of resources. Our economic trade is itself an ecological process that transports resources and organisms across the globe [see telecoupling]; our civilization alters community composition and function wherever we can make a living, all the while affecting global biogeochemical cycles. Our framework for understanding the role of social process on ecosystem function is just in its infancy, and there is no vernacular language for describing the built environment as an ecosystem. This is not how our society understands the environments we inhabit. One goal of the Global Urban Soil Ecology and Education Network (GLUSEEN) is to increase the exposure of urban citizens to the important role that soils play in maintaining ecosystem health.

Within the discipline of ecology, there exist frameworks to describe the outcomes of human behavior in terms of ecosystem process. For instance, biotic homogenization (BH) describes a process of convergence among biotic communities; generally communities become more similar (converge) when endemic specialist species are extirpated and generalist species come to dominate. Convergence is a process that is often applied to understanding the effect of both urbanization and agriculture, where the implied (or assumed) mechanisms are generally anthropogenic disturbance and/or facilitated dispersal. In this instance, BH describes how land-use conversion (habitat loss) drives local extinctions, while the cultivation of exotic species facilitates the dispersal of a common set of organisms. In this context, BH helps to explain the paradox of high urban and peri-urban biodiversity concomitant with significant global biodiversity loss. Endemic species go extinct, while opportunists thrive in the human-disturbed landscape (see, for example, this). To bring the mechanisms into focus, BH has been reformulated somewhat as the Urban Ecosystem Convergence Hypothesis, which relates structural changes in the built environment to changes in community process. It predicts that if urban landscapes are constructed and maintained in a similar manner (causing a convergence of habitat characteristics across biomes), then their biotic community and ecosystem processes should converge as well. For example, in their paper entitled “Ecological homogenization of urban USA,” Groffman et al. show that the practice of maintaining irrigated lawns causes a convergence of biophysical conditions across biomes within urban areas in the United States; in temperate forest systems, land-use conversion to lawns increased surface temperatures by reducing shade and evaporative cooling that normally occurs in the canopy. Whereas irrigating arid land for lawns increased evaporative cooling at the ground level, causing the two environments to converge with respect to temperature as well as humidity.



Image recreated from Pouyat et al., 2017
Journal of Urban Ecology.

The Global Urban Soil Ecology and Education Network (GLUSEEN) applied the Urban Ecosystem Convergence Hypothesis to urban soils. We sampled from soils that occurred within four different land-uses, which were categorized to represent land-use histories that are typical of urbanized landscapes (published here). These four categories were reference, remnant, turf and ruderal. Reference sites served as our control; they were sites located outside of the urban matrix, which are representative of the historic state of the ecosystem and are being managed to mitigate human impact. Many reference sites were areas set aside for habitat conservation. Remnant sites are similar to reference sites in community structure but occur within the urban matrix, and thus exposed to urban environmental factors. Turf sites were defined as sites under management to maintain a turf-grass system, which include municipal, residential, or park lawns. Ruderal sites were defined as sites that have experienced recent and substantial disruption of the soil profile, and typically were areas with a history of demolition or construction activity. Using these land-use and cover categorizations, we asked whether specific types of land-use and cover (both largely an outcome of cultural processes) caused physicochemical properties and microbial communities of soils to converge; and whether these changes result in a convergence of function among these soils.



Within-group variance of edaphic factors, among land-use;
2a shows the convergence of soil pH, OC, and N
under turf and ruderal land-use relative to the reference;
2b shows the divergence of P and K under turf
and ruderal land-use relative to the reference.
Recreated from: Pouyat et al., 2015.

As an assessment of the soil habitat characteristics, and to test the first question, we measured edaphic features such as phosphorus (P), nitrogen (N), and potassium (K) availability, as well as other characteristics such as organic carbon (OC) and pH. To quantify and identify the archaeal, bacterial, and fungal community, and to test the second question, we used quantitative PCR and amplicon sequencing. And finally, as a test of soil function, we conducted a decomposition experiment using tea bags in each of the study sites (see here). First, we found that in fact some physicochemical properties of soils converged under turf and ruderal land-use and cover types. Soil pH, OC, and N in particular converged. However, not all characteristics converged as K and P actually diverged under urban land-use (Figure 1).  We believe that it’s likely that cultural differences in how fertilizers are formulated (N vs N:P vs N:P:K fertilizers) and the variability in their rates of application may explain the increased variability among P and K nutrients; while N is also enriched systematically by fossil fuel combustion that leads to consistent atmospheric deposition of N in urban areas (and thus convergence). The convergence of soil pH is likely related to the widespread use of concrete, and the resulting concrete dust in urban areas; the calcium oxides and carbonates found in concrete effectively act as a liming agent as they dissolve, buffering soil pH towards a more alkaline condition. And finally, while specific land-use and cover types might have differing effects on the soil OC concentration, the effects within each land-use are consistent; disturbances often result in lower OC, while irrigation and fertilization in the absence of disturbance may actually increase carbon storage in soils. Thus, cultural factors may drive convergence of some habitat characteristics while causing other habitat characteristics to diverge.



Within-group variance of the fungal, bacterial, and archaeal
communities; the fungi converge in ruderal sites
relative to reference,the bacteria do not converge,
and the archaea converge in the turf and ruderal sites.
Recreated from Epp Schmidt et al., 2017.

Our next question was whether communities of organisms living in the soil converge under similar land-use and cover. We found that of the three phylogenetic domains making up the soil microbial community, the archaea and fungi exhibited a marked convergence, while bacteria did not (published here). We also showed that this convergence may be driven by different ecological factors. For example, we found that convergence in the fungal community was largely due to the loss of ectomycorrhizal fungi (ECM), while the convergence of archaeal communities was due to the increased abundance of ammonia oxidizing archaea. ECM function as symbionts with woody plants, and thus are highly reliant on the abundance of their host species. When land is converted from forest to any non-forested urban land-use, it appears that there is no longer viable habitat for most of these species. Archaea, on the other hand, actually increased in overall abundance under lawn use, and their community became dominated by organisms that derive energy from the oxidation of reduced nitrogen species. This means that, unlike for fungi, the N enrichment of urban environments is favorable to these members of the archaeal community. Moreover, since absolute abundance increased and richness also increased, it appears to be the case that the metabolic differentiation among archaea allowed convergence to occur without competitive exclusion. Therefore our dataset demonstrates the two mechanisms by which convergence might happen; a loss of unique species, or an increased dominance of just a few species that can be found in all sites. It is of course possible that both mechanisms operate in tandem to cause convergence.

The urban landscape represents the zenith of human development; it is the cultural hub of our civilization and the control center for our social process. It is also the area with the highest land-use intensity, and therefore is the most significantly disrupted ecosystem. With our dataset, we are able to show some effects that human culture has on ecosystems; the cultural process that drives the globalization of our economy and the homogenization of our global culture also has global impacts on ecosystem process via the local decisions that land managers make. Our data demonstrates that human culture may cause either a convergence (soil pH, N and OC) or divergence (P and K) of soil habitat characteristics, and that microbial communities may (fungi, and archaeal) or may not (bacteria) converge as a result. We were also able to determine multiple mechanisms that drive convergence. The fungi likely converged due to our impacts on cover (reducing the abundance of host species), while the archaeal likely converged because of our N enrichment of the urban landscape (enhancing the fitness of organisms that rely on certain forms of N metabolism). Thus there are specific interactions between human alteration of the landscape and biotic community response. The impacts of urbanization on the function and makeup of the biotic community may be long lasting, and indeed, might even outlive civilization itself. In 2008, when he published his book The last flight of the scarlet macaw, Bruce Barcott could scarcely have known that within a decade scientists studying the Mesoamerican landscape would be using the color of tree leaves (by reflecting laser light off of them from high altitudes) to discover the location of lost ancient Mayan structures. It is remarkable that urban centers, constructed and abandoned nearly a millennium ago, can still be discovered using their legacy impact on the biotic community.

 

Read the full manuscript here:

Epp Schmidt, D. et al. 2017. Urbanization erodes ectomycorrhizal fungal diversity and may cause microbial communities to converge. Nature Ecology & Evolution doi:10.1038/s41559-017-0123

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Soil ecologists define research priorities

By Nico Eisenhauer, Professor for Experimental Interaction Ecology, German Centre for Integrative Biodiversity Research

Many, if not most, of the ecosystems on Earth are dependent on, or substantially influenced by, interactions and processes occurring within and among the planet’s soils. The remarkable biodiversity harbored in soil provides essential ecosystem services, and the sustainable management of soils has attracted ever-increasing scientific attention. Although soil ecology emerged as an independent field of research many decades ago, and we have gained important insights into the functioning of soils, there still are fundamental aspects that need to be better understood to ensure that the ecosystem services that soils provide are not lost and that soils can be used in a sustainable way. In a recent Opinion Paper (Eisenhauer et al. 2017; https://doi.org/10.1016/j.pedobi.2017.05.003), we highlight some of the major knowledge gaps that should be prioritized in soil ecological research. These research priorities were compiled based on an online survey of 32 editors of Pedobiologia – Journal of Soil Ecology. The questions were categorized into four themes:

(1) soil biodiversity and biogeography;

(2) interactions and the functioning of ecosystems;

(3) global change and soil management;

(4) new directions.

While some of the identified barriers to progress were technological in nature, many respondents cited a need for substantial leadership and goodwill among members of the soil ecology research community, including the need for multi-institutional partnerships, and had substantial concerns regarding the loss of taxonomic expertise. Global efforts such as the Global Soil Biodiversity Initiative suggest that meaningful collaborative endeavors among researchers could be possible and may represent a starting point from which to build this concerted effort to address the questions presented in our Opinion Paper.




Interaction in the soil caught in the act: a predatory mite from the family Bdellidae
feeding on the springtail Sminthurinus elegans. Image by Andy Murray.


Reference:

Eisenhauer N, Antunes PM, Bennett AE, Birkhofer K, Bissett A, Bowker MA, Caruso T, Chen B, Coleman DC, de Boer W, de Ruiter P, DeLuca TH, Frati F, Griffiths BS, Hart MM, Hättenschwiler S, Haimi J, Heethoff M, Kaneko N, Kelly LC, Leinaas HP, Lindo Z, Macdonald C, Rillig MC, Ruess L, Scheu S, Schmidt O, Seastedt TR, van Straalen NM, Tiunov AV, Zimmer M, Powell JR (2017) Priorities for research in soil ecology. Pedobiologia 63: 1-7.

http://www.sciencedirect.com/science/article/pii/S0031405617301063

 

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Ploughshares are swords… if you are an earthworm

By Olaf Schmidt (University College Dublin, Ireland) and Maria J. I. Briones (University of Vigo, Spain)

 

Let us beat our swords into ploughshares” is an evocative slogan used by peace builders around the world. However, when it comes to earthworms, ploughs are swords that can kill you and destroy your homes.

We have known for a long time that tillage operations impact large soil macrofauna such as earthworms, directly by mechanical injury and indirectly by destroying their channels and burying surface plant residues. For example, a study from Ireland showed that very intensive soil cultivation for potato production (including grubbing, destoning and ridging) can virtually eliminate earthworm populations. Many such individual studies exist around the world. For the first time, scientists have assembled all available primary research results from individual field experiments from the five continents and analysed them together in a meta-analysis, a statistical tool that allows us to look for (and quantify) common effects or trends across many independent studies.

The scientists from the University of Vigo, Spain, and University College Dublin, Ireland, extracted data from 165 publications, from across 40 countries, published between 1950 and 2016. Each of the studies investigated earthworm populations under conventional tillage (inversion tillage such as mouldboard ploughing to 25 cm depth) and other forms of reduced tillage (such as soil loosening up to 25 cm depth and no tillage).

The findings published in the scientific journal Global Change Biology show a systematic decline in earthworm populations in soils that are ploughed every year. The deeper the soil is turned, the more harmful it is for the earthworms.

Results show convincingly that most forms of reduced tillage will increase earthworm numbers and biomass. Among the five forms of reduced tillage analysed separately, the most positive effects were seen in no-tillage (direct drilling) and also superficial tillage or soil loosening <15 cm (non-inversion tillage). Another form known internationally as Conservation Agriculture (which involves retention of at least 30% of organic residues or mulching) also prompted a significant increase in earthworm populations (see figure). These reduced tillage practices are increasingly being adopted world-wide due to their environmental benefits in terms of erosion control and soil protection. They are economically attractive because not having to plough brings savings in cost, labour and fuel.



The effect of the different forms of reduced tillage treatments on earthworm abundance (a) and biomass (b) as a percentage of the control (conventional ploughing). Treatments were No-tillage, Conservation Agriculture (CA), Shallow soil loosening (SSL), Deep soil loosening (DSL), and other forms of Reduced tillage (RT). Mean effect and 95% confidence intervals are shown. Sample sizes are shown on the right of each treatment (number of control–treatment pairs / number of studies). Reprinted with permission of John Wiley & Sons Ltd. from Briones MJI and Schmidt O: Conventional tillage decreases the abundance and biomass of earthworms and alters their community structure in a global meta-analysis. Global Change Biology DOI:10.1111/gcb.13744. Copyright © 2017 John Wiley & Sons Ltd.

The study also analysed ecological groups of earthworms (namely epigeics, anecics and endogeic) and the most common species separately. According to the findings, the earthworm species most vulnerable to tillage are the larger ‘anecic’ earthworms that create permanent vertical burrows and feed on soil surface residues. Of all species included in the study, the nightcrawler (Lumbricus terrestris) suffered most under conventional ploughing. The small ‘epigeic’ earthworms that live in the organic litter layers of soil and convert debris to topsoil were also found to be highly susceptible.

The study also analysed ecological groups of earthworms and the most common species separately. According to the findings, the earthworm speices most vulnerable to tillage are the larger ‘anecic’ earthworms that create permanent vertical burrows and feed on soil surface residues. Of all species included in the study, the Nightcrawler (Lumbricus terrestris) suffered most under conventional ploughing. The small ‘epigeic’ earthworms that live in the organic litter layers of soil and convert debris to topsoil were also found to be highly susceptible.



Lumbricus terrestris is an ‘anecic’ species,
seen here foraging at the soil surface at night.
Photo credit: Olaf Schmidt

These findings can be translated into advice for farmers in different parts of the world. Switching to reduced tillage practices is a win-win situation for farmers because they save costs and, in return, larger earthworm populations help in soil structure maintenance and nutrient cycling. The larger the populations of these beneficial soil organisms, the more of these beneficial functions a farmer will get – for free.  Earthworms are also good indicators of soil quality and soil health, it is easy to check for a farmer of his/her soil is in good status by just digging up a bit of soil and checking worm numbers (there are simple guides available that show how many worms you should expect in a spade-full of soil). We know of course that there is much more life in the soil (bacteria, fungi, mites, springtails, nematode worms etc), but to study them is difficult for non-specialists.  Earthworms are so useful because everybody can look for them easily.

Coming back to our opening slogan, when we speak about earthworm populations and soil protection, perhaps we should say “Let us beat our swords into ploughshares… but use them less often”. Reduced tillage practices will restore productive earthworm populations and help maintain soil structure, nutrient recycling and other biological soil functions.

 

Read the original manuscript here:

Briones MJI, Schmidt O (in press) Conventional tillage decreases the abundance and biomass of earthworms and alters their community structure in a global meta-analysis. Global Change Biology DOI:10.1111/gcb.13744

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Soil fauna responses to ecosystem disturbances



Soil fauna are central to soil ecology
Photo by R. Carrera-Martinez

By:  Dave Coyle, Southern Regional Extension Forestry and UGA – D.B. Warnell School of Forestry and Natural Resources.  Find Dave on Twitter @drdavecoyle, and check out his website: http://southernforesthealth.net/ Mac Callaham, USDA Forest Service – Southern Research Station.  See more about Mac at https://www.srs.fs.usda.gov/staff/447

 

Soil fauna are central to the field of soil ecology.  For a generation, scientific giants Drs. Dave Coleman, Dac Crossley, and Paul Hendrix at the University of Georgia - Odum School of Ecology taught a course on soil biology and ecology largely centered on fauna, training numerous ecologists and taxonomists.  After these three retired from UGA, however, the class went on a multi-year hiatus.  In 2013, Dr. Mac Callaham, a soil ecologist with the USDA Forest Service, and Dr. David Coyle, a forest health specialist with Southern Regional Extension Forestry and the University of Georgia, teamed up to bring the course back.  As part of the course, students from the Warnell School of Forestry and Natural Resources, Odum School of Ecology, and departments of Plant Sciences and Crop and Soil Sciences, conducted a literature review on the impacts of various land disturbance factors on soil biota and wrote term papers synthesizing their findings.  Student papers were combined and edited into the first-of-its-kind review on the impacts of disturbances on soil fauna, and was published in the journal Soil Biology and Biochemistry (http://www.sciencedirect.com/science/article/pii/S0038071717301530).



Publications on soil microbes have increased at a greater rate
than soil fauna. Modified from Coyle et al. 2017

Mac is well-known for his work with earthworms, and other macroinvertebrates, and in particular their responses to land-management activities.  Dave’s PhD research examined the impacts of a suite of non-native root-feeding weevils in the Upper Peninsula of Michigan.  Together, we have often lamented the fact that soil fauna – especially macrofauna – rarely get the attention they deserve (our opinion, obviously).  But, in researching this paper, we found that publishing trends confirm this notion (see right).  In recent years, there has been a disproportionate increase in papers dealing with soil microbes compared to soil fauna.  Anecdotally, with the exception of earthworms, ants, and a select few economically important taxa (think crop pests like corn rootworm, or citrus root weevil), soil fauna are somewhat ignored.  And for those of us who work on soil fauna, that isn’t cool.  Sure, we know that microbes are important actors in soil ecosystems, but they don’t act alone, and the soil ecology research community has amassed years of scholarship indicating that macrofauna can have big influences on the biomass, composition, and activity of soil microbes.

 

So, we acted like any good scientists and we wrote about it (and it was peer-reviewed, even!).  We synthesized what was known (and unknown) about the impacts of natural and anthropogenic disturbances on soil fauna.  For some taxa, there was very little information (published or otherwise) available.  For others, information was plentiful.  We know there are a LOT of complex interactions between organisms, disturbances, and their environments - especially when dealing with multiple scales (see below).  One of our challenges was capturing this heterogeneity and adequately conveying what it meant, in some cases, when information was only available from one scale.  Fortunately, there are some really good long-term studies in existence (e.g. Luquillo LTER: http://luq.lternet.edu/) that were great sources of information.  We examined natural disturbances like wind damage, flooding and water stress, drought, and fire; invasive plants and invasive invertebrates; and fire.  In each case we reviewed the impact of these factors on fauna in different parts of the soil (i.e. epigeic and endogeic/anecic).




Types and scale of ecosystem disturbances
Modified from Coyle et al. 2017


In what may hardly be considered groundbreaking to anyone who does research below the soil surface, the take home message was “it depends,” and it depends on a lot of different things.  A lot. The impacts of particular disturbances vary depending on the specific fauna in question.  It also matters at what scale – you may see fine-level impacts (e.g. in a plot) but at the watershed scale there is no discernable impact on fauna communities.  Short time duration versus long time duration also matters, as certain taxa are much better at “rebounding” after a disturbance than others.  Additionally, the issue of giving an accurate name to the organism under study (i.e. taxonomy) is important.  Most studies of soil fauna do not identify organisms to the species level, which makes interpretation of results incredibly difficult (not to mention complicating the comparison of data across studies).

 

Our review reaffirmed some things we already knew: belowground ecology is hard, scale is important, and there isn’t enough taxonomy in the world.  It also highlighted some things we didn’t know: the pace of publishing work on soil microbes is much greater than that dealing with soil fauna.  As one would expect, there are some significant gaps in the knowledge.  But that’s why we’re all here working and reading this blog, in the hopes of filling those gaps.

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Soundtrack for Soil Biodiversity



Summer storm rolls across the Colorado Prairie
Image by E. Bach

By Elizabeth Bach, Executive Director, Global Soil Biodiversity Initiative, Colorado State University

 

Summer is arriving at the Global Soil Biodiversity Initiative secretariat headquarters in Colorado, USA. Like many of you all, we’re gearing up an active field season, some long hours in the lab, and maybe a road trip or two.  I always look forward to this shift in work as it usually allows me to jam out to some great music in the background. Inspired by a recent groundwater-themed playlist from the European Geosciences Union, I set out to put together a Soundtrack for Soil Biodiversity!

The playlist captures several musical styles.  Each of the songs on the list relates to soil or a soil organism, either literally or metaphorically.  Stream the full playlist in the link below this list.

Do you have a favorite song about soil biodiversity?  Share with me, and we’ll keep building the list!  I’d love to hear what everyone is listening to all around the world!

 

  1. Another one Bites the Dust by Queen: OK, I know they don’t mean “bite the dust” literally, as say an earthworm might, but this song has pushed me through some long days of sample processing.

  2. The Trees by Rush: Classic rock exploration of forest succession: oaks vs. maples competing for light! No musical exploration of research examining the differences in C and N cycling in arbuscular mycorrhizal fungi dependent maples in contrast to ectomycorrhizal fungi dependent oaks, but you can read up on that here: Phillips et al. 2013. New Phytologist
  3. Nematode by Charlemagne: Nematodes crawling through the soil, decomposition, erosion, this song is about the role soil organisms play in renewing life.
  4. Dirt by Florid Georgia Line: “You came from it, and some day you’ll return to it.” This country-western ballad captures a lifetime lived on the red ultisols (acrisols) of the southeast USA.
  5. I like Dirt by the Red Hot Chili Peppers:  The title speaks for itself.
  6. Termite Hop by the Beatnik Termites: Rock & Roll teenage love story song, “everybody’s got to do the termite hop.”  Curious about the role of eusocial insects including termites and ants in soil food webs? Check this recent review: King 2016, Soil Biology & Biochemistry
  7. Centipedes by Hot Box Machine: Become one with centipedes on the run, lost in all the fun. Connect with the centipedes and feel at one with the Earth.
  8. Centipede by Knife Party: Centipede vs. Tarantula, scientifically informative electronic dance music. Check out this video of a real centipede taking down a tarantula.
  9. Buggin’ Out by A Tribe Called Quest: A rapper wrestles with the pressures of fame “in between the girt and the dirt.”
  10. Wormship by Illiterate Light: Exploring one’s feelings through the experience of an earthworm in a rainstorm
  11. Earth by Sleeping at Last: Life reflects the processes of the Earth, digging into it tells many stories of disaster and hope.
  12. Cio da Terra (The Earth in heat) by Milton Nascimento: Brazilian ballad praises the "miracle" of soil generating life (in Portuguese).

 

 

Bonus tracks (not on Spotify)

All my Friends are Insects by Wheezer: Well, one of their friends is an earthworm, which is not an insect, but still a lot of fun!

 

Dichotomous Key by Billy Kelly & Molly Ledford: This focuses on trees, and it’s a great musical introduction to a dichotomous key:

Trees by Molly Ledford & Billy Kelly

 

If you’re working on some writing projects and want music to focus, check out the instrumental version of Aesop Rock’s Music for Earthworms.

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The Ground Beneath Us: From the Oldest Cities to the Last Wilderness, What Dirt Tells Us about Who We Are

By Paul Bogard, Assisstant Professor, James Madison University, Harrisonburg, Virginia USA

 

I came to soil from the stars. In my first book, The End of Night: Searching for Natural Darkness in an Age of Artificial Light, I did my best to call attention to the value of darkness and the many costs from light pollution. Most people in modern cities and suburbs—especially the younger among us—have no idea what a real starry sky looks like, and no idea of what they’re missing. The fact that life on earth evolved with bright days and dark nights, and needs both light and darkness for optimal health, is something most of us never think about. When I began to imagine the next book I would write, I quickly realized the same is true of soil.

            It’s hard to believe that so few people understand how important soil is for our survival. Hard to believe, perhaps, until you hear the estimate that we in the west spend on average 90-95% of our time inside, cut off from the natural world. My new book, The Ground Beneath Us: From the Oldest Cities to the Last Wilderness, What Dirt Tells Us about Who We Are, began when I heard this stunning number. It wasn’t long before I realized that when we do walk outside, we mostly walk on pavement or asphalt. We have gone from being intimately in touch with the natural ground at our feet to being almost completely separated from it. From there, I began to see how this literal separation was symbolic of our separation from the different grounds that give us our food, our water, our energy, and even our spirit. I decided to explore the many costs of this separation, and the value of knowing the life at our feet.

            I certainly could have written an entire book about the wonderful subject of soil. But I decided to place our relationship with soil within the larger subject of our relationship with the ground. I was fascinated by the notion that the oldest spiritual traditions and the newest sciences tell us the same thing about the ground—that it’s alive, and that we would be wise to treat it carefully. I was intrigued as well by the different kinds of “grounds” that give meaning to our lives, such as battlegrounds and burial grounds, hallowed ground and ground we deem sacred. I was—and continue to be—especially interested in the question, Why do we live so separated from and ignorant of that which sustains us?



Becoming grounded on the Alaska tundra
Image from P. Bogard

            From the paved ground of New York, London, and Mexico City, to the grounds that would inspire me to ponder the sacred—the Nazi death camp at Treblinka in Poland, the wild tundra of Alaska’s southwest—I went looking for answers. Between these bookends I placed the chapters in which I sought to share the amazing, mysterious, known-more-than-ever and yet still-barely-known world of soil. The similarities to the stars came back to me here. The numbers so large they bend our brains as we try to comprehend. The galaxies upon galaxies beyond anything we now know. And especially, the way that once you know what’s out there, you never look at the sky—or, in this case the ground—the same way again.

Everywhere I go now I find myself looking at the ground with wonder. This is the feeling that stays with me after writing this new book. Wonder that everything growing—even us, if we pause long enough to realize—is anchored in soil, dependent on its life for our life. If I had one wish for the new book, it would be that it help more people to realize this, and bring to soil the attention and respect it deserves. It would be that we would walk outside, look down, and know what we have been missing.

 

Learn more about Paul and his writing at http://www.paul-bogard.com/ Tags: 

30 Questions for Soil Protistology



Saccamoeba
Image from S. Geisen

By Stefan Geisen, Department of Terrestrial Ecology & Laboratory of Nematology, Netherlands Institute of Ecology, Wageningen, The Netherlands

 

 

With 47 authors of the soil protist initiative, a group closely linked to the GSBI, we have just compiled an important opinion paper to highlight 30 key open study questions dealing with soil protists. We show that protists are a highly-underrepresented group of soil organisms, especially compared with the other microbial bacteria and fungi. However, there are several reasons why protists are important and should be prioritized or at least be included in future soil biodiversity studies!

 

 

 

 

Protists are incredibly diverse!
  • Protists are taxonomically highly diverse; they represent the majority of the eukaryotic tree of life where fungi, plants and animals are small monophyletic groups.
  • We also highlight that protists are morphologically diverse, ranging from bacterial sized taxa of few micrometers to several centimeters.
  • Furthermore, protists span a huge functional diversity of organisms; in addition to the mainly considered bacterivorous taxa, many protists feed on fungi, nematodes, a huge diversity is parasitic to animals and pathogenic in plants.
  Protists are of key importance in soils!
  • Without protists, bacteria and fungi would have few enemies!
  • Protists are a key link in soil food webs- without them most soil animals had no food!
  • Without protists, plants would suffer from nutrient limitation!




Fig. 1. Common free-living soil protists as visualized by size (lengths), morphology and phylogenetic affiliation
Modified from Geisen et al. 2017


This is just a fraction of what we highlight in the paper. For more info, check out the paper published in Soil Biology and Biochemistry. More updates on the soil protist initiative can also be accessed directly at https://soilprotists.wordpress.com/ and https://www.researchgate.net/project/Soil-protist-initiative.

 

Don’t hesitate to get in touch with us and be connected- protists are a key part of future research!

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Six ways soil biodiversity sustains us!

By Elizabeth Bach, Executive Director, Global Soil Biodiversity Initiative & Sustainable Leadership Fellow at the School of Global Environmental Sustainability, Colorado State University This blog post first appeared in the HUMANnature blog from the School of Global Environmental Sustainability, Colorado State University  

As a 5-year-old, one of my favorite things to do was play in the dirt.  My cousins and I would make “soup,” a mixture of soil, leaves, twigs, and some unfortunate bugs, with just enough water to easily stir.  The “recipes” were endless; from which part of the yard we got the soil, the ratio of twigs to leaves, the addition of a stray earthworm or insect all contributed to different “soups.”  As a kid, this play occupied my imagination for hours at a time.  As an adult, the interactions of soil and organisms, dead and alive, continue to fascinate me.  Just like a hearty stew, soil provides nutrients and energy to all organisms living aboveground, including people, and sustains ecosystems and humanity now and into the future.  How, you ask?  Well, here are 6 ways soil biodiversity sustains us!

 


Clockwise from top left: nematode, psuedoscorpion, burrowing owl, tardigrade. Photo credit: D. Robson, A. Murray, M. Knoth, N. Carrera.

 

 

  1. It’s Alive! Soil is home to ~25% of all described species on Earth.  These range from microscopic nematodes and tardigrades to small psuedoscorpians and even larger animals like burrowing owls.  But wait, there’s more!  The majority of soil species likely have not even been described by scientists.  That means soil holds numerous biological mysteries and likely supports far more than 25% of all species on Earth.  Soil is a frontier for exploration and discovery, right beneath our feet.
  2.  


    Left: Legume Gliricidia growing with maize in Zambia, Right: mushrooms. Photo credit: ICRAF, D. Endico

     

     

  3. It grows our food! Some soil organisms people can eat directly, like mushrooms, truffles, and some insects.  Other soil organisms help fruits, vegetables, and grains grow by recycling nutrients from dead plant material.  All plants, including crops, need nutrients, such as nitrogen, phosphorous, and potassium, from soil.  Most soils have limited reservoirs of these nutrients.  But dead plants, perhaps from the previous year’s crop, retain many of these nutrients in their tissue.  Soil organisms like insects, earthworms, micro-invertebrates, fungi, and bacteria break down dead plant material, releasing nutrients for new plant growth.  Soil organisms are critical to recycling nutrients to grow food and support sustainable farming.
  4.  


    Left: a child receives medication, Right: bacteria colonies can vary in color, shape, and texture. Photo credit: hdptcar, P. Turconi/Fondazione Istituto Insubrico di Ricerca per La Vida

     

     

  5. It helps us live long and prosper! Soil organisms impact our health and lifestyles in both negative and positive ways.  For example, anthrax, tapeworms, histoplasmosis, and brain encephalitis are all caused by soil organisms, including bacteria, pictured above.  Valley Fever, or coccidioidomycosis, is a nasty and often deadly disease caused by the soil fungus Coccidioides immitis native in the southwest USA.

    Other soil organisms can cure many diseases.  In soil, all these organisms live together in a community.  Some organisms have evolved defenses, such as antibiotic compounds, that can minimize disease agents.  Antibiotics like penicillin, originate from soil organisms, and can combat many illnesses caused by bacteria or fungi, like pneumonia and strep throat.  Soils are also a promising frontier in the development of new pharmaceuticals, which may reduce antibiotic resistance.  People around the world, like the child receiving a shot in the photo above enjoy healthy lives thanks to soil organisms.

  6.  


    Reindeer grazing. Photo from pixabay.com

     

     

  7. It supports wildlife! Nutrient cycling from decomposition also supports food for wildlife that we enjoy viewing, hearing, and in some cases, hunting.  Without soil biodiversity, wildlife would not have plants, fruit, and nuts to eat.  Much like the effects on people, however, soil can also harbor disease organisms that can make wildlife sick, or even result in death.  For example, in July 2016, anthrax, a soil bacterium, released from thawing soil in Siberia killed >1500 reindeer. That’s right, Santa’s sleigh may be running slow this year because of a soil organism!
  8.  


    Soil organisms filter excess nutrients and pollutants from water, keeping it safe for wildlife and humans. Photo credit: R. Kayser, Dept. Foreign Affairs & Trade

     

     

  9. It filters water! As water moves through soil, soil organisms use the nutrients and minerals dissolved within it.  This effectively removes excess nutrients and some pollutants before water reaches ponds, streams, lakes, rivers, etc.  This is important not only for clean drinking water for animals and people (pictured above), but also for healthy fish and other aquatic organisms.  In many areas of the US, there is extra nitrogen and phosphorous in surface waters, in part due to run-off of fertilizers from crop fields and lawns.  When there is excess nitrogen and phosphorous in water, algae use it grow, consuming large amounts of dissolved oxygen.  Reduction in dissolved oxygen can cause fish and other large aquatic organisms to suffocate, generating a “dead zone,” also known as hypoxia.  The 2016 “dead zone” in the Gulf of Mexico was estimated to be about the size of Connecticut (5,898 square miles)!  Soil organisms can reduce this nutrient load, and the number of algae that grow, keeping our waters oxygenated and healthy.

    Soil biodiversity also helps store water in soil.  Earthworms, insects, and other animals create tunnels, which allows water to flow into the soil more easily during precipitation events.  In addition, soil organisms generate organic matter, made up of the byproducts of biological metabolism (think compost) that gives soils a dark color.  Because soil organic matter is charged, it holds water between organic molecules, allowing soil to store more water than clay, slit, and sand particles alone.

  10.  


    Cyanobacteria (top left, right) oxygenated Earth's atmosphere, Soil organisms cycle greenhouse gases like carbon dioxide (bottom). Photo credit: K. Siampouli, Futurilla, Art by MarkAC, EU Joint Research Center; Numbers calculated by US DOE, Biological & Environmental Research Information System.

     

     

  11. It recycles the air! Before plants covered our planet, cyanobacteria (pictured above) used simple carbon molecules and minerals from rocks as energy sources.  This released oxygen, which eventually built up in the atmosphere to levels that could support the evolution of more microbes, plants, fungi, and animals, like us.  We still rely on plants and soil organisms to maintain enough oxygen in the atmosphere for us to live. Soil organisms also cycle greenhouse gasses, which trap heat near the surface of Earth (pictured above, bottom panel). 

    Soil organisms can both pull greenhouse gases, like carbon dioxide, out of the atmosphere and respire carbon dioxide back into the atmosphere.  When soil organisms decompose dead material, they use carbon from the tissue as an energy source.  Some of that carbon is used for growth and reproduction.  That carbon can stick around in soil for weeks, years, decades, or even longer.  Some of the carbon is used for respiration, just like when we breath, soil organisms produce carbon dioxide.  This adds up to a lot of carbon!  As shown above, soils contain 2,300 gigatonnes of carbon.  By comparison, respiration by soil organisms contributes only 60 gigatonnes of carbon back to the atmosphere.  We can help soil organisms potentially reduce greenhouse gasses in the atmosphere through land management choices like ecosystem restoration, conservation farming practices, and increased urban green space.

 


Left, Mycen chlorophos, a bioluminescent fungus found in Asia, Top right, Fuligo septica is also known as “dog vomit slim mould,” Bottom right, scanning electron image of a tardigrade Photo credits: S. Axford, Stu’s Images, J. Méndez, and M.J.I. Briones

 

 

Soil organisms are truly the unsung heroes of sustainability.  We need them. Wildlife needs them.  Fish need them. Ecosystems need them.  Soil biodiversity not only sustains life on earth, it is intrinsically fascinating.  From bioluminescent fungi (pictured far left) to dog vomit slime mold (pictured top right) and adorable tardigrades (pictured bottom right) soil is home to some awesome living things.  It is organisms like these that captured my adult imagination long after my “soup” making days as a kid.  The best part is, it is not imaginary at all.  The real world beneath our feet is astounding and essential.  We all need living soil, so future generations can play and thrive in the dirt.

All images, except the reindeer, are from the Global Soil Biodiversity Atlas and available for free download (pdf) and use! 

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The Marvel of Soil Biodiversity

By Leo M. Condron, Professor of Biogeochemistry, Lincoln University, Canterbury, New Zealand

This article appears in the Autumn 2017 issue of New Zealand Turf Management Journal

We have been granted permission to share this article in full.

Click the image on the left to view the full article. Tags: 

Illustrating Soil Life



Vorticella
Image by: Katelyn Weel

By Katelyn Weel, artist, Gransherad, Norway

 

 

I first discovered the beauty and elegance of microscopic creatures as a student of Environmental Sustainability at Lakehead University in Orillia, Ontario.  During my studies,  I  worked as a research assistant analyzing protozoa and diatoms in natural freshwater biofilms.

In 2013 I left Canada and started working at VitalAnalyse in Norway, where I observed soil in the microscope and started learning about soil life as it applies to agriculture. Despite having studied environmental sustainability for four years, until I started this work I really had no idea about what was going on in the soil. Once I started to learn just how complex and intricate below ground ecosystems are and how little we really know about them, I developed a much greater appreciation for soil, and I started to see the need for a very different approach to agriculture.

In my role at VitalAnalyse, I occasionally help lead public workshops, seminars, and demonstrations about life in the soil. During these events, I have noticed that the smallest things most people can easily relate to are usually mites or springtails that can be seen with the naked eye. If it requires a microscope, it starts to feel abstract. Even solid and detailed images taken from scanning electron microscopes are clinical looking, alien, out of context, or simply too “sciency” for most non-academics to connect with. If only we could take pictures of rotifers, protozoa, and bacteria in their natural habitat with regular cameras, to simply observe them as we would any other animal with our own eyes.

I decided to try using my imagination and my experience with the microscope to illustrate what it might look like if we could simply shrink down and observe rotifers, flagellates, ciliates, and other soil organisms face to face in their natural habitat.

In each drawing, I aim to demonstrate some of the complexity and diversity of soil ecosystems, including small details you might not notice at first glance, such as tiny flagellates, bacteria, or threads of fungi in the background. I want to illustrate the organisms in a way that they are both realistic and beautiful, and to draw the viewer into the mysterious world beneath us.




Rotifer
Image by: Katelyn Weel



Testate amoeba
Image by: Katelyn Weel


The drawings have been well received here in Norway. I’ve realized that there is a lack of illustrations like this in our field, so I am reaching out to let more people know that these drawings exist, and I’d love to do more.

My gallery of soil life illustrations can be found here. There are more drawings in progress, and the site will be updated as I continue adding to the collection. I hope that my artwork can help more people connect with soil biology, and bring them a little closer to the invisible and underappreciated world of microbiology that is so important to our everyday lives.

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Chasing rabbits: How do soil communities respond to herbivore mammals? Part II



Rene van der Wal, ecologist at University of Aberdeen,
surveys the plant community on Isle of May.
Photo by: Walter Andriuzzi

By Walter Andriuzzi, Postdoctoral Fellow, Colorado State University

 

In the previous post I described how herbivore mammals, from rabbits to cattle, can affect the soil food web, and how difficult it is to find general patterns across different places. Here I summarize what we found in a meta-analysis of field studies that had compared soil communities inside and outside exclosures (plots of land that were fenced to keep herbivores out).

First, the effects of herbivores depend on climate. For example, soil respiration rate is lower with herbivores than without in subarctic ecosystems, whereas in temperate ecosystems it is higher with herbivores than without. Second, the effects of herbivores vary between trophic groups in the soil food web, and between soil biological functions. For example, unlike respiration, soil microbial biomass and nitrogen mineralization rate do not respond consistently to herbivores in either climate type, whereas they both tend to decline when herbivores are present under arid climates. In subarctic sites, root-feeding nematodes are negatively affected by herbivores, whereas predatory nematodes appear to do just as fine.

Third, the effects of herbivores vary also within trophic groups in the soil food web. Take for example two of the most widespread and abundant groups of soil animal decomposers, oribatid mites and springtails: the former decrease in abundance when herbivores are present, whereas the latter do not show a consistent response. Fourth, the effects of herbivores depend on the herbivore species, in a way that can be at least partly predicted based on their body size: the smaller the herbivore, the more likely its effects on the soil organisms to be neutral, or even positive (that is, increasing biological activity or abundance of soil organisms); the larger the herbivore, the more negative its effects tend to be.

How do our results compare with previous theory? An established framework predicts that herbivore presence has positive effects in the highly productive systems, and negative effects in poorly productive systems. However, the results of our meta-analysis support these predictions only in part. Herbivores have negative effects in low productivity biomes, for example in tundra, but most highly productive systems also exhibited negative effects of herbivory on belowground communities. The big exception was soil respiration in temperate grassland. Moreover, we found that climate is more important than vegetation type; and that herbivore identity and body size are also important.

In our meta-analysis, we did observe that responses tend to shift to negative with increasing body size, and an explanation may well be physical disturbance. A more recent framework of belowground responses to herbivory focused on the role of large herbivores on soil compaction. In fine-textured soils, trampling by cows reduces soil pore size and limits oxygen and/or water availability, leading to declines in mineralization rates. We could not test the importance of soil texture in our meta-analysis, because too few of the available studies quantified it rigorously.



Conceptual model of how herbivore size and climate determine
the effect of herbivores on the soil community.
Modified from Andriuzzi & Wall 2017

Based on our results we developed a conceptual diagram which partly integrates those previous frameworks, by envisioning gradients of herbivore body size and/or climate limitations. Small herbivores, for example the rabbits on the Isle of May, may have limited effects on soil biological activity, or even enhance it by fuelling the soil food web with their excreta and/or more palatable plant resources. Large herbivores, for example cattle (especially if at high density), may lead to physical disturbance such as compaction (because of trampling) and exposure of soil to erosion and atmospheric agents (because of great reduction of plant cover) so the net response belowground is negative. Likewise, with a temperate climate herbivore presence could promote soil biological activity, though not to a great extent if the system is productive enough (as likely was the case on the Isle of May). In ecosystems more limited by aridity, cold, etc., herbivore presence begets the opposite response due to its physical effects on soil. All this is a simplification - different groups of soil organisms may not respond in the same way – but it offers a mechanistic framework to make sense of our findings, and to generate new hypotheses to test.

There are several areas with limited data that challenge the applicability of our general frame work.  There were very few studies from the tropics that we could include in the meta-analysis. As a result, while we know a good deal on the effects of reindeer on soil organisms in subarctic tundra, we know next to nothing on those of elephants and impalas in African savannah. Another major surprise was how little some major groups of soil organisms have featured in herbivore exclusion experiments. Protists, which are essential in the soil food web, are lacking altogether from the meta-analysis; earthworms, which have huge effects on soil and plants, were also poorly represented. I hope that our meta-analysis will spur new research to understand how herbivores change their ecosystems not only aboveground, but also belowground.

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Chasing rabbits: How do soil communities respond to herbivores? Part I



Terror of the undergrowth:
A young rabbit on the Isle of May.
Photo by: Walter Andriuzzi

By Walter Andriuzzi, Postdoctoral Fellow, Colorado State University

 

June 2011. I am standing near the edge of a vertical cliff above the Atlantic Ocean. Two puffins glide and land gracefully on the rocks despite their almost comically short wings. I am on the Isle of May, a wind-swept Scottish island with some of the biggest colonies of marine birds in Europe. Not far from the guano-streaked cliff there is a small plot of land enclosed by a fence. This is an exclosure, and its task is to keep out the rabbits that graze the vegetation on the island with the efficiency of a lawnmower. The grass outside, punctuated by cushions of forbs like Silene uniflora and Armeria maritina, is ankle-high; inside, the grass brushes my knees. And this is not the only difference. Outside the exclosures, the ground is littered with rabbit faeces, which fertilizes the soil. The plants grazed by the rabbits undergo changes in their chemical make-up, and tend to release more carbon into soil as root exudates. The rabbits also change the environment physically: with a reduced plant cover, the ground is more exposed to atmospheric fluctuations; and of course, rabbits make burrows. Unsurprisingly, excluding rabbits is a big deal for the plants. But what happens belowground?

This is a question that ecologists Richard Bardgett and Rene van der Wal have investigated since the early 2000s. They set up these exclosures on the Isle of May to test the idea that the effects of herbivores on a soil biological community depend on the fertility of the system. The Isle of May is an ideal natural laboratory to test this framework, because it has two levels of soil fertility: near the seabird colonies the soil is enriched in nitrogen of marine origin (courtesy of the birds’ guano and ammonia), whereas in the middle of the island it is not. And yet, three years after the exclosures had been established, rabbits had the same (weak) effects on the soil food web regardless of whether the plots were close to the coast or not.

In 2011, as a master’s student of van der Wal, I seek to find out if things have changed eight years since the experiment started. As a proxy for the soil food web, I study the nematodes, microscopic roundworms that live in the water films between soil particles. They occupy almost all trophic levels belowground: there are nematodes that feed on bacteria, nematodes that feed on fungi, nematodes that feed on microalgae, nematodes that feed on plant roots, and nematodes that feed on nematodes. Because they are so diverse and extremely abundant, they have a big impact on ecosystem functioning; in turn, of course, they are affected by what happens to the plants and the soil where they live. And yet, once again we find only small differences in the soil food web inside and outside the exclosures, despite obvious differences in plant biomass and plant diversity.




One of the exclosures on the Isle of May.
Photo by: Walter Andriuzzi


The difference between what happens above and below ground is in no way peculiar to this experiment. Many other studies found surprisingly weak effects of herbivore mammals on soil fauna and microbes. Other studies found big effects, but not in a consistent direction: in some herbivores increased the abundance of soil organisms or the rate of soil biological processes, while in others the opposite was observed. In an attempt to better understand general patterns in belowground responses to herbivory, I recently performed a meta-analysis, an analysis of results from numerous previous studies, on herbivore-plants-soil interactions to find global commonalities in how soil organisms and the biological processes they regulate respond to herbivores. Stay tuned for the next post to discover what I found out!

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Belowground visions of life: Soil makes Art: exhibition and mural in April 2017



A handsome mite.
Image by: Ed Reynolds

By: Dr Tancredi Caruso, School of Biological Sciences and Institute for Global Food Security, Queen’s University of Belfast

 

In the past, worldwide and across cultures people knew that soil plays a critical role in supporting our life cycle. In modern urban environments, too many still think that soil is just dirt. Ed Reynolds, an artist supported by the Leverhulme Trust, and I (a soil ecologist) will be trying to overturn that view to show the kaleidoscopic beauty of the biological universe called soil. We believe that art is the key to make people aware of the beauty and importance of soil biodiversity in our life. We will soon exhibit our work in Belfast: on 1st and 22nd of April 2017 we will have two events taking place respectively at the Ulster Museum and the Girdwood Hub in Belfast, Northern Ireland. Meanwhile, the project has also illustrated Soil and War, a chapter from Richard Bardgett’s book Earth Matters (Oxford University Press): you can read more about that here.




Emerald springtail
Image by: Ed Reynolds



Soil biodiversity is vital to humans!
Image by: Ed Reynolds


The project will have a conclusive mural event: Northern Ireland murals have become iconic, reflecting local cultures and history, but very often also the divisions caused by the Northern Ireland conflict (also known as the Troubles). Especially in Derry and Belfast, the last decade has seen the replacement of sectarian murals with new murals that aim to rebuild deteriorating relationship across communities. Here, we aim to rebuild the deteriorating relationship between humans and soil, and for this reason we have decided to realise a mural in the middle of Belfast: we want to offer an artistic vision of soil to deliver a message of peace to all cultures in the world. A workshop with children from various backgrounds will take place in April (exact date yet to be decided) and the mural will then be painted. The walls have been identified, and details will follow soon: in the next post, we will show you the mural idea...stay tuned!




Transformation of beetle larvae
Image by: Ed Reynolds


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The supply of Soil Functions in European Soils

By: Rachel Creamer (Wageningen University, Netherlands) and Francesca Bampa (Teagasc, Ireland)

Why do our Soils matter?



Visualization of Sustainable Development Goals with
ecosystem functions supporting all goals.
Credit: Azote Images for Stockholm Resilience Centre

The Sustainable Development Goals were established in 2015 by the United Nations to to end poverty, protect the planet, and ensure prosperity for all. There are 17 goals in total and each goal has targets to be reached over the next 15 years. Recently the Sustainable Development Goals were rearranged by the Stockholm Resilience Centre to highlight the importance of soil, land, water and climate as they underpin all the remaining development goals. Soil is essential for society as a whole, as it provides us with our food, raw materials for fuel, clothing, as well as an environment in which we can flourish as a cultural society.

Soil is specifically mentioned in four of the 17 Goals only, these include; No. 2 dedicated to Zero Hunger in the World, No. 3 on Good Health and Well-being, No. 12 on Sustainable Production and Consumption and No. 15 Life on Land. While soil was not considered in the original text of the goal No. 13 Climate Action, the agreements made at the Paris Climate COP 21, in November 2015 highlighted the role of soils in Climate Action as well, in particular for carbon sequestration.  

In Europe, there has traditionally been a focus on soil functions and threats, rather than soil health. In 2006, the Thematic Strategy for Soil Protection was developed looking at the role of soils in society. This document highlighted the main soil threats (compaction, erosion, salinity, acidification, landslides, loss of biodiversity, sealing, decline in organic matter and contamination) and also the positive message of the functions that soil supplies to society (substrate for plant growth, habitat for biodiversity, nutrient cycling, carbon sequestration and cycling, water quality and regulation, platform for infrastructure and store for archaeology). Following the Soil Strategy, a European Legislation was developed looking at minimising the threats to soils and enhancing soil protection. This was named The Soil Framework Directive. However, this Directive was never accepted by all member states, with the focus on soil threats and was removed from policy discussions in 2014.

Therefore, the approach now is to look at the role of soils from a positive perspective and show what soils can do for us as a society and how we can sustainably manage this precious resource. 

What do we want from our soils?

We must first decide what are the main soil functions that we want the soil to deliver? In an agricultural context, this is primarily to provide food, fibre and fuel – whether that is cereals, beef, milk, biomass crops, or wood etc. However, in the production of food, we must also ensure that we do not diminish the capacity of the soil to also carry out the other soil functions necessary to ensure sustainable food production. This dual optimisation of both agricultural supply and the capacity of the soil to meet environmental requirements can be at times challenging.



Soil provides many functions including clean water,
agricultural production, biodiversity, and nutrient cycling.
Credit: Schulte et al. 2014

What do we mean by soil functions? In agricultural systems, we consider the following functions that the soil supplies:

  1. Primary productivity - providing maintenance for the growth of food. feed and fibre, this includes; root support, water and air through the soil structure.
  2. Cycling of external nutrients – capacity of a soil to absorb and store and slowly release nutrients to crops over time.
  3. Water purification – ability of a soil to remove excess nutrients and pollutants from water before it reaches the water source.
  4. Carbon storage and cycling – capture and cycling of carbon sources from the atmosphere and plants, that carbon then provides strength to the soil structure and nutrient reserve.
  5. Biological habitat – provides a home to the largest diversity of biological organisms on the planet. These soil organisms drive most of the processes that take place in soil.

 

Managing our soils lives at the heart of farming systems. So understanding what functions our soils are best at delivering is essential to get the best from our land. While all soils are capable of delivering on all functions, some soils are better than others at specific soil functions. That is traditionally how we decided where to grow which crops, which areas to leave to nature and which soils are suited more grassed based or forest land use types.

 

Managing our soils across a range of scales

Every day, farmers make decisions on how they manage their land and soil, including decisions on fertilisation, ploughing, reseeding, weight of tractors, application of pesticides, herbicides and insecticides, etc. At the same time, national and European policy makers make long-term decisions on how to manage their soil resources at larger scales, such as how to work towards meeting greenhouse gas emission targets through optimising carbon sequestration in soils.

Therefore, the contemporary challenge for researchers and stakeholders is to link the decision making on land management across scales, so that the practicalities of how farmers make decisions on a daily basis is reflected in policy formation.

We cannot expect all soil functions to be delivered simultaneously to optimal capacity, but with careful decision making we can optimise our soils to provide multiple functions. In reality not all functions can be optimised to their full capacity at the same time, as the conditions required to deliver one function may be in contrast to those to deliver another function. A good example of this, is the requirement for nutrient cycling which may compete with the with the ability of the soil to support the function habitat for biodiversity, where external inputs include sewage sludge derived materials, which can have a significant impact on the soil biology. However, in many cases multiple functions can work in synergy together and in most scenarios three out of five soil functions can be optimised together.




European landscapes, Top: Terraced fields, credit: Rusu Teodor, USAMV Cluj
Lower left: Agricultural field, credit: Eckhard Pieper, LWK Niedersachsen
Lower right: Irish Soil Information System project (Teagasc, Ireland)


Mapping and Assessing Ecosystem Services:

In addition to the soil functions approach, there is an increasing focus on mapping and assessing soil based ecosystem services. The Food and Agriculture Organisation of the United Nations (FAO) defines soil based ecosystem services as; “Ecosystem services are a way of putting a value on biodiversity by looking at what it does and how we value the function that the soil performs”.

MAES (Mapping and Assessing Ecosystem Services) is part of the Action 5 deliverable of the Biodiversity Strategy. The Directorate General for the Environment of the European Commission are currently in a process of developing guidelines for the mapping and assessing of soil ecosystem services. These guidelines will be provided to Member States within Europe, who will be asked to identify and map the soil ecosystem services within their country.

 

What the future holds for soils in Europe

While there is no current legislation for the protection of soils in Europe, there is certainly increasing recognition of the role of soils in society. There is a lot of on-going research which is identifying the role of soil functions and how we can optimise the supply of these functions in a sustainable manner. One such project is the LANDMARK project, funded by the Horizon 2020 European Research Funding. This includes representative scientists, advisors, land managers, and policy makers from across Europe, China and Brazil. This project is looking at the role of soil functions at three different scales:

  1. Local scale – to help farmers optimise the soil multi-functionality on their farms
  2. Regional scale – to identify how soil functions vary across the different climatic zones of Europe and how we measure soil functions.
  3. An assessment of policies that can ensure that we ‘make the most of our land’, from both an agronomic and environmental point of view at a global scale.

 

For more information on LANDMARK see: http://landmark2020.eu/

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The choice of agricultural landscape has an influence on crop (and soil) health


A young pistachio orchard (foreground) in a larger
maize cropping system on the banks of the
Orange River, Prieska, South Africa.

By Prof. Schalk vdM. Louw, Centre for Plant Health Management, University of the Free State, Bloemfontein, South Africa.

This article appeared previously in the Ons Eie magazine, April 2007

 

Agricultural landscapes are by implication complex adaptive systems, tailored by anthropogenic interference. The relationship between structure and function, e.g. trophic structures, diversity - productivity connections and nutrient fluctuation patterns of such landscapes is fundamental in their organization, whether self-driven or regulated. In cropping system landscapes, we are obligated to understand the processes that influence the abundance, richness and diversity of biota that impact on plant health and ultimately crop yield.

Crop health management therefore requires that, amongst others, an understanding is developed on how the architecture of landscapes influences pest population dynamics and their interaction with the surrounding environment, natural enemies and agents of control. Agricultural landscapes, on whatever scale, implies habitat fragmentation to a lesser or larger degree and we need to understand the implication of such events with regard to ecosystem processes.

Understanding the processes which drive agricultural landscapes, especially in semi-arid regions, is a prerequisite towards analysing patterns, which in turn lead to sound policy and management decisions. This article therefore makes the point that, in general, crop system analysis in the context of diverse agricultural landscapes across South Africa is lacking and needs to be addressed. The main research question derived from this, in turn, is in which manner spatial (i.e. shape, size and structure) and temporal (i.e. seasonality) features of agricultural landscapes and the crop value chains emanating from them, link to the population dynamics and trophic structure of insects and other biotic agents.

Understanding the population dynamics and trophic structure of insects in crop agroecosystems is vital in the sustainable management of such systems. However, this would be an incomplete picture of the actual scenario, should the diversity, identity and architecture of the particular landscape within which these systems fall not be taken into consideration. Bring into the equation the fact that agricultural landscapes are always under the pressure of anthropogenic influences at different scales and the issues suddenly become intricate. What follows below is a breakdown of the array of direct and indirect factors that influence the identity of agricultural landscapes within which crops are cultivated and which have a bearing on their value to the farmer/producer and ultimately the end-user.

 

A holistic approach

Fundamental would be that the management of landscapes influenced by humans be geared towards the enhancement of biodiversity and ecosystem function. This must be regarded in the context that agricultural landscapes in an area unavoidably result in fragmented habitats, which, in turn, are the drivers of complex localized processes and community structures. Biodiversity, as such, is an organizing principle in agroecosystem management, since it determines the degree of relative stability in a disturbed environment. Landscapes planning should therefore protect and enhance biodiversity and support ecosystem processes of succession, energy flow, and hydrological and nutrient cycling. In this context gaps should be bridged between agricultural policy, land-use and biodiversity indices. A further objective   should be a marriage between the approaches of social scientists and ecologists when providing relevant advice.

Space and time are basic entities in ecosystem analysis. Thus, analysing landscapes and their biotic inhabitants in terms of spatial and temporal dynamics is crucial in providing an informed perspective. In this context landscapes patterns arise which originate from exogenous (e.g. climate) and endogenous (e.g. competition) processes and feedbacks.

A holistic approach to investigations of this nature is always a strong recommendation, since it provides insight into system self-organization. Any deviation, which is out of sync with the optimal functioning of the system, is an interference which could jeopardize sustainability. In harsher, semi-arid regions this could have far reaching effects with regard to establishing new/underutilised crops which are required to address different utilisation commodity groups.

 


Porosphere soil from a wheat field, western
Free State province, South Africa.

Landscape fragmentation and insect population dynamics

There are implications of insect populations in habitat fragments. In such a scenario the sequence of events are: crop cultivation > natural habitat destruction > sharply contrasted habitat mosaics > threat to biodiversity > collapse of trophic structures. The implication of such a scenario is that populations of beneficial insects collapse, whilst detrimental / pest insects are boosted. In other words, fragmentation sensitive species could be influenced in terms of trophic position, population dynamics variability and vagility. There are also further ramifications that relate to pure habitat loss, fragment size and shape, fragment isolation, fragment quality, edge effect and landscape structure.

A further crucial landscape ecology issue exists in terms of the temporal frameworks link for above ground – below ground multifunctional linkages between organisms. This is not only an important barometer for soil health and ultimately crop health, but also for microbial-insect-plant interactions. Interaction strength levels, on the whole, matter very much in landscapes and determine their complexity. Overall the specific biome and regional setting of a particular landscape is the ultimate determining factor of soil and crop health integrity.

In fragmented landscapes habitat edge effects (i.e. greater species richness and abundance in the transitional zone between habitats than in the habitats themselves) also reveal interpretive complications and may be the foremost explanation of many of the negative effects arising from fragmented habitats. One such negative effect is that habitat edges can serve as ecological traps, whereby an anthropogenic change in an organism’s environment leads individuals to use misleading cues of habitat quality. Specifically the size and internal habitat of a fragmented patch and its relationship with ‘edge effect’ needs further investigation.  Fragmentation affects populations along a number of routes that relate toedge effect, i.e. area identity, degree of isolation and area age.

 

Soil quality and the role of bioindicators

Another important factor in agricultural landscapes is soil quality. Insect herbivory, as part of the trophic structure of a particular landscape, increases litter quality and decomposition indices and as such influences ecosystem nutrient cycling and accelerates the production of soil organic matter. It also acts as a persistent control mechanism for ecosystem processes.

If bioindicators can be identified in a system in this context and used to indicate disturbances in an environment, the relevance emanating from this could be significant.  In terms of sound management strategies, analysing insect structures in heterogeneous environments (landscapes) to determine optimal diversification in systems, can act as an important guidance towards establishing environmentally acceptable pest management strategies.

 

Conclusion

Ecosystem services are the benefits that humans (society) obtain from ecosystems. Agricultural landscapes and their soils also provide multiple ecosystem services, the successful management of which depends on the recognition of the relationships between the processes and the structures that maintain a healthy system. Although science continuously yields new environmentally friendly agricultural practices and techniques, the sustainable development of a system will ultimately depend on a farmer’s ability to understand and utilize these advances.

 

For more on soil health in South Africa and the Soil Ecosystem Research Group (SERG) go to www.sergsa.org.

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Plant diversity speeds-up belowground recovery

By Ryan Klopf (Virginia Dept. Conservation and Recreation), Sara Baer (Southern Illinois University Carbondale), Elizabeth Bach (Colorado State University), and Johan Six (Swiss Federal Institute of Technology)

 

“Prairie was, in fact, a community of plants and animals so organized as to build, through the centuries, the rich soil which now feeds us.”  -Aldo Leopold, Prairie: The Forgotten Flora (1942)*




Tallgrass prairie restorations planted with high plant diversity (left) and low plant diversity (right)
Photo credit: Ryan Klopf


The tallgrass prairie of the U.S. Midwest is one of the most endangered ecosystems in the world, with >99% of the ecosystem converted to cultivation in some states.  Restoring farmland in the Midwest back to tallgrass prairie has been of public interest since the days of Aldo Leopold.  Much of this restoration work, however, has focused on reconstructing native plant communities with the assumption that animals and ecosystem functions will follow in time. Many land managers have also questioned whether their efforts to restore diverse plant communities has added benefit to soil recovery from the long legacy of agriculture. Ecologists have conducted many studies to test whether biodiversity influences ecosystem functioning (e.g., aboveground productivity). Most tests, however, been performed at small scales with controlled numbers of species in relatively simple plant or aquatic communities (e.g., <20 species).  Many of these studies show that higher biodiversity has a positive effect on ecosystem functioning, particularly aboveground. The application of this theory to the practice of ecological conservation and restoration at large scales and under less controlled conditions has been limited. To fill this application gap, we measured the rate of belowground recovery in former agricultural fields restored to high diversity prairie and low diversity grassland (Klopf et al. 2017).  



Soil from a high plant diversity restoration.
Photo credit: Elizabeth Bach

 

The fields used in this study were restored using two different approaches.  One set of fields were restored through the USDA’s Conservation Reserve Program (CRP), a federal program that pays landowners to convert marginal crop land to perennial vegetation. A main goal of this program is to reduce and prevent soil erosion.  As such, fields restored to prairie through the CRP program generally include <10 plant species.  Previous work has shown the low diversity CRP approach can increase soil carbon storage over decades (Baer et al. 2002, 2010).  The set of fields used in our study were restored by The Nature Conservancy, with the goal of reconstructing diverse tallgrass prairies communities to protect rare plants and animals.  As such, these restorations are planted with >30 locally collected native prairie plant species and actively managed using frequent fire to reduce weeds (non-native plants).  All fields were located on similar soils within a two county region of Illinois, USA.  Fields under both practices ranged in age (time since restoration) from 2-22 years.

 

Our findings showed that restoring and managing for more diverse plant communities can improve recovery of belowground biology and functioning in predictable ways. Specifically, we found greater accumulation of roots, more predictable recovery of soil microorganisms (bacteria and fungal biomass), more rapid improvement in soil structure (less compaction), and less nitrogen available for loss from the system  in prairie restored and managed for high plant diversity relative to the low diversity grassland plantings.  Thus, the hypothesis that biodiversity promotes ecosystem functioning is relevant to large-scale conservation and restoration practices on the landscape. 

 

Read the original manuscript here:

Klopf RP, Baer SG, Bach EM, and Six J. 2017. Restoration and management for plant diversity enhances the rate of belowground ecosystem recovery. Ecological Applications 27: 355-62.

 

Additional reading:

Baer SG, Kitchen DJ, Blair JM, and Rice CW. 2002. Changes in ecosystem structure and function along a chronosequence of restored grasslands. Ecological Applications 12: 1688–701.

Baer SG, Meyer CK, Bach EM, et al. 2010. Contrasting ecosystem recovery on two soil textures: implications for carbon mitigation and grassland conservation. Ecosphere 1: art5. OPEN ACCESS

*This handwritten essay is included in:  Sayre, R.F. 1999. Recovering the Prairie. University of Wisconsin Press. Madison, Wisconsin

 

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Globally, a wealth of local knowledge of soil biota exists



Categorisation of farmers’ knowledge of soil
biota, based on the ‘knowledge-practice-belief’
complex in ethnoecology. From Pauli et al. 2016

By Natasha Pauli, Lecturer in Geography in the UWA School of Agriculture and Environment, University of Western Australia

 

The 2016 publication of the Global Soil Biodiversity Atlas presented a compelling depiction of soil biology to a wide audience. The need for the Atlas is reflected in the fact that soil biodiversity is undervalued by society, and rarely considered within policy frameworks to protect either soil quality or biodiversity. However, this relative lack of interest in soil biological health does not hold true across all segments of society. If you were to go and ask someone who makes their living from the land what they know about soil health and soil biology, you may get a far more informed answer (as discussed last month by Hannah Birgé).

My interest in what farmers know about soil biota was sparked in the hills of Central America, while investigating the spatial distribution of soil fauna in a smallholder landscape in remote Honduras. Ultimately, I wanted to know whether the soils beneath particular trees that were left within cropping fields attracted soil animals, with flow-on effects for soil quality. There were dozens of species of trees to examine and the topography and soils were highly variable - it was difficult to know where to begin! We decided to start by asking the farmers what they knew - and what they had to say was fascinating, reaching far beyond simple descriptions of which parts of their farm supported the greatest density of earthworms (read about it here).

As I soon learned, while these types of questions may be asked in the field, they are often not deemed worthy of in-depth investigation or publication. The volume of literature on farmers’ knowledge of soil organisms pales in comparison with that on scientists’ knowledge of the topic. Even the field of ethnopedology (which is concerned with local ecological knowledge of soils) has tended to emphasise the identification, mapping, management and use of different local soil types within agroecological systems, with little enquiry on the living components of soils. Historically, social scientists and soil biologists have worked together infrequently. So, does this lack of information on how farmers view and use soil biota reflect an actual dearth of knowledge, or simply an understudied field of enquiry?

To address this question, I worked with colleagues Professor Lynette Abbott at the University of Western Australia, Dr Simoneta Negrete-Yankelevich at INECOL Mexico, and Dr Pilar Andrés at CREAF, Spain to undertake a systematic, worldwide review of peer-reviewed and high quality grey literature on local knowledge of soil fauna in agriculture. Our review, published last year in the open access journal Ecology and Society, turned up 60 studies that highlighted some aspect of farmers’ understanding of soil fauna, drawn primarily from Africa, Latin America and Asia, with a handful from the USA, Europe and Australia. Our findings show that there is a potentially rich body of knowledge on soil biota, but one that is rarely elicited.



Illustration of farmers’ perceptions of the effect of soil invertebrates on components of a smallholder farming system in Honduras. Redrawn from Pauli et al 2012 for the Global Soil Biodiversity Atlas.

There was a very broad range of ways in which farmers understand and use soil fauna. The most common example was the use of particular taxa (usually earthworms and beetle larvae) as an indicator of soil quality, cited in around two-thirds of studies reviewed. There were also many instances of local observations of species’ ecology, behaviour and life history, as well as exquisitely detailed taxonomies of invertebrate life. Some authors documented management practices such as deliberately using the action of soil fauna to improve soils for cultivation, by encouraging the activities of ants and termites to improve soil structure and increase organic matter content on marginal land. Soil invertebrates can also have cultural and spiritual significance, which influences how people perceive these organisms.

Farmers are rarely deliberately or deeply consulted by researchers on their knowledge of soil biota, soil ecology, or soil ecological processes. We encourage soil biologists to work together with social scientists to explore this important topic. In particular, researchers should explore not just observations of soil fauna, but



Map of the location of 60 reviewed studies on farmer knowledge of soil biota.
From Pauli et al. 2016

how these organisms are considered in agricultural activities, and the belief systems and cultural values that influence agricultural systems and perceptions of soil life. Our review found very few studies on local knowledge of fungi, rhizobia, or soil microbes, with most existing research limited to visible organisms - this is another area ripe for further exploration.

 

There are very important reasons why soil biologists should do more to understand how farmers use and value soil life. A deeper understanding of this topic can lead to more effective development of collaborative extension programs, policies and management initiatives directed at maintaining healthy, living soils. We give some examples in the paper of how this has occurred in smallholder and broadacre systems from Mexico, Nicaragua and Australia. Giving farmers the tools to measure elements of soil biological activity in their own fields can empower them to undertake their own experiments and analysis, and ultimately support adaptive and sustainable management of agricultural landscapes.

 

Further reading:

Pauli, N., Abbott, L.K., Negrete-Yankelevich, S., Andrés, P. (2016) Farmers’ knowledge and use of soil fauna in agriculture: A worldwide review. Ecology and Society 21, 3. http://dx.doi.org/10.5751/ES-08597-210319

Pauli, N., Barrios, E., Conacher, A.J. and Oberthür, T (2012) Farmer perceptions of the relationships among soil macrofauna, soil quality and tree species in a smallholder agroforestry system of western Honduras. Geoderma 189-190: 186–198. http://dx.doi.org/10.1016/j.geoderma.2012.05.027

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Understanding the role of biodiversity in our soils


Soil profile, Irish Soil Information System
Photo by Brian Reidy

By: Rachel Creamer (Professor, Wageningen University, Netherlands), Dorothy Stone (Leeds University) and Paul Massey. This article was originally published when all three authors were working at Teagasc, Johnstown Castle, Wexford, Ireland. The article was published in Organic Matters Magazine in 2013.

 

Soil Biodiversity encompasses a huge array of life on the planet. In some cases, 5 tonnes of animal life can live in one hectare of soil.5 The variety of soil biodiversity is also quite astounding ranging from bacteria, which are from 1-100 μm in size (i.e. completely invisible to the eye) through to the macrofauna which are on average 2 mm or larger in size and can be easily seen, such as earthworms, ants, woodlice, centipedes etc. The size of an organism is extremely important as this controls its life cycle and its impact on the soil functions. While an individual bacterium is tiny, it fits into minute spaces and there can be 3,000,000 to 500,000,000 bacteria present in 1 g of soil.  The role of soil biota in the soil is essential for everyday functions and ecosystems services to take place such as water filtration, nutrient cycling, organic matter breakdown, development of soil structure, plant growth and pollination.

In terms of agricultural production, the intensification of management systems has led in some cases to reduced soil biodiversity due to increased mechanisation, addition of chemical based fertilisers and application of mono-culture systems. The organic farming approach acknowledges the key role of soil biodiversity in the production of food and fibre. However, in order to maintain yields in low input organic systems, every single addition needs to be used as efficiently as possible.  As little of the nitrogen from a green manure, or carbon from the ploughing back in of stubble, should be lost.  To ensure that none of these additions are lost, it is essential to achieve as diverse a below-ground community as possible. The more diverse the biological community i.e. more species, sizes of organisms, feeding habits, life cycles etc the more potential to capture and cycle nutrients within farm and therefore provide an added source of nutrition to the organic production system.

There are some key groups of biology which are important in the delivery of these soil functions these include; bacteria and fungi (due to the large number present in soil and their role in decomposition of organic matter), nematodes (which are well know for the suppression of plant diseases and regulation of nutrient cycling) earthworms which are the “engineers” of the soil and are responsible for the large scale movement of soil particles and organic matter in the soil that define soil structure. 

The biological community structure in soils is quite similar to how all animals live on the planet. Different species live in different parts of the soil, some in water films, others in air spaces and the feeding strategies (known as a food web) are very complex. The food webs that exist below ground (a chaotic interlinked tangle of organisms that eat dead organic material and the organisms that in turn eat them), are more efficient and resilient to stresses like drought or disturbance if they have a complex structure, with many pathways for nutrients to move along as they are transformed from waste material to a form that crops can use. Within these foodwebs certain species are quite important as they feed upon other species or are fed upon by others. These species are vital for the flow of nutrients through the system. The presence of these keystone species helps us assess potential problems in the soil. In this article, we will discuss the role of nematodes and earthworms as case studies as they are considered a good bioindicators (show changes in soil health) due to their central role in foodwebs and soil structure.


Omnivore Nematode
Plant-feeding nematode,
Dolichodoridae tylenchorhynchus
Plant-feeding nematode

Nematodes are aquatic animals and within soil (“free-living” nematodes as opposed to “marine” nematodes or “plant parasitic” nematodes), live in the thin water films around soil particles and within soil pores1.  It is estimated that there are between 40,000 and 10,000,000 species of nematodes2 and there can be up to a million individuals per m2 in soil3.  Sometimes called “roundworms”, these small invertebrates (0.2 – 2.5 mm long) are impossible to see in soil with the naked eye, though they are visible when they are extracted into water, where they look like short thin white hairs. Nematodes are too small to affect the structure of soil in the way that earthworms can4, but they have the potential to contribute massively to the efficiency of nutrient cycling and thus the amount of carbon, nitrogen and other important elements available for crop growth.  When nematodes are present in soil at a high level of biodiversity, they contribute to the complexity of these nutrient cycling food webs.  They are able to do this because they feed on a wide variety of different sources within the soil.  Each species of nematode has specialised mouth parts, therefore some nematodes can eat bacteria, others feed on fungi, there are some nematode species that only eat plants and others that have the ability to eat all of these things (see diagram below for the different mouth parts associated with the different feeding types).  There are also predator nematodes that prey on other nematodes and sometimes even other soil fauna such as enchytraeid worms.  This ability to provide so many varied and different connections between the pathways along which nutrients are cycled mean that nematodes are an intrinsic and important group of species for maintaining soil fertility.



Earthworms at work

Earthworms are considered the farmer’s friend, as they are essential for the maintenance of soil structure. As I explained in my last article maintenance of soil structure should be one of the main considerations for any organic farmer, as it influences so many other functions in the soil such as nutrient availability, seed propagation, rooting, drainage etc. There are three main trophic groups of earthworms;

  • Surface living (epigeic) worms – which feed on litter and manure and break these down on or near the surface of the soil;
  • Night feeding (anecic) worms which have vertical burrows which come up to the surface from 30- 50 cm down, these include the well known Lumbricus terrestris species and they feed on the surface decomposing plant material which they pull down into the permanent vertical burrows;
  • Soil-eating (endogeic) worms – these worms make horizontal burrows by eating the soil as they move through the soil and excreting it to fill the space as they move through. The bacteria living in the guts of these worms transform the nutrients in the soil material making it more available on excretion. 

While a lot is known about the role of nematodes and earthworms in our soils, much of the soil biology is not yet understood for it’s role in soil functions. We also have very little understanding about which species are present where. Therefore, there is a great need to further our knowledge on this and to understand what baseline is required for a healthy biodiversity in soils of different land use types to deliver the functions we require as a society. Teagasc is involved in a large scale European project (Ecofinders) which is looking into this and will report on the variety of soil biology found in different land-uses across Europe and how some of these species are important for the delivery of soil functions as listed above.



Farmers & scientists examine a soil profile

Additional Resources

1Ecology of Plant and Free-Living Nematodes in Natural and Agricultural Soil, Neher D.A., Annu. Rev. Phytopathol, 2010, 48: 371-394

2The Role of Nematodes in Ecosystems, Yeates G.W., Ferris H., Moens T., Van Der Putten W.H., In Nematodes as Environmental Indicators, Ed Wilson J.W., Kakouli-Duarte T., 2009, CAB International, London UK.

3SSU Ribosomal DNA-Based Monitoring of Nematode Assemblages Reveals Distinct Seasonal Fluctuations Within Evolutionary Heterogeneous Feeding Guilds, Vervoort et al., PlosOne, 2012, 7:10

4Ecology of Plant and Free-Living Nematodes in Natural and Agricultural Soil, Neher D.A., Annu. Rev. Phytopathol, 2010, 48: 371-394

5European Atlas of Soil Biodiversity (available in English & French)

 

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