Soil is the most diverse place on Earth, and we need to protect it

By Mark alan anthony, Swiss federal institute for forest, snow, and landscape research

A rich forest soil harboring over 1,000 fungal species! I’m wearing gloves to exclusively measure what lives in soil versus on our bodies.

How do you advocate for something most people cannot see, smell, feel, taste, or touch? Soil includes so much of the ground beneath our feet, and it is home to an exceptional diversity of life. There is no zoo for soil organisms, and I have a hard time imagining a soil fungus becoming as emblematic as the WWF panda (though I would be delighted to be proven wrong). So how can we change the way we think about soil life?

Our recent publication quantified soil biodiversity to understand what fraction of Earth’s life lives belowground. Answering this question enables researchers, environmental practitioners, and policy makers to advocate differently for soil biodiversity because our estimate is much bigger than once thought. We estimate that 59%, plus or minus 15% (the error range of our estimate), of life resides in soil from the smallest (viruses) to most complex life forms (mammals). The most diverse group of organisms in soil are microbes, with fungi being the most specialized microbial group to soils (90% of species live in soil), while the least biodiverse groups in soil are mollusks and mammals, at just 20% and 3.84% of species, respectively.

I often consider what might happen if we lose significant soil diversity. Unlike a lot of non-soil dwelling, larger organisms, many soil organisms cannot live without cooperation and quite literally need diversity. Many soil bacteria lost the ability to synthesize essential amino acids, and they must cross-feed (i.e. share) amino acids with other bacteria in the soil or they will die. Tens of thousands of fungi lost the ability to grow alone and rely on living host plant roots in soil to obtain energy. And soils that we experimentally manipulate to kill-off microbes fail to support plant life compared to soils with diverse, living microbial communities.

Plants grow vigorously with living microbial communities. Healthy green plants have diverse, living microbial communities whereas yellow plants have been experimentally grown without a diverse, living microbial community.

When our paper was first published, I was discussing different ways to frame it with my husband, who is also the artist that illustrated the soil organisms for our manuscript, Michael Dandley (check out Fig. 3 in the paper). He said that he viewed our effort akin to taking a census. We make a census to know where people live and how we should distribute power and resources. The results of our “census” of biodiversity is therefore at extreme odds with the current distribution of resources for conservation and restoration. Very few resources flow towards the conservation of soils. While we are not trying to compare a soil nematode to an Orangutan or to constrain efforts to preserve and protect biodiversity aboveground and in the oceans, we hope the results of this work make a case that we need to focus much more on soils. This will look like designing new strategies to measure and monitor soil biodiversity, initiatives to protect critical areas of soil biodiversity (even if there aren’t any threatened organisms aboveground), and policy makers advocating for more resources towards soil conservation and restoration in the face of the biodiversity crisis.