Changes in the relative abundance of fungal functional groups and dominant taxa due to soil warming are associated with losses in total soil carbon
Dr. Gregory J. Pec
Assistant Professor, University of Nebraska Kearney, USA
Figure 1. Laetiporus sulphureus (chicken of the woods or sulphur shelf) found on decomposing logs in two soil warming experiments at Harvard Forest, Petersham, Massachusetts.
Global warming poses major challenges to the health and functioning of forests, with the direction and strength of such effects on forest ecosystem processes such as carbon cycling remaining uncertain. Several mechanisms have been proposed to explain changes in soil carbon cycling dynamics. Of these, that the loss of soil carbon from warming is driven by changes in microbial community structure is important, since warming may impact certain microbial taxa with specific functional capacities that ultimately influence rates of soil carbon cycling. In particular, soil fungi are vital in mediating several of these ecosystem processes including carbon and nutrient cycling. They form diverse and spatially variable communities as plant symbionts, decomposers, and plant pathogens. Although a general finding is that soil fungal abundance often declines in response to warming, it is less clear how certain functional groups (i.e., symbionts vs decomposers) are differentially sensitive to shifts in temperature. Toward this goal, we built upon previous research in temperate deciduous forests and assessed changes in the diversity and composition of soil fungi following soil warming. Since fungal responses to warming have been previously shown to be associated with changes in soil chemistry, a secondary objective was to assess key soil chemical properties and examine any relationships between soil fungi and soil properties.
Figure 2. Soil warming experiments established at Harvard Forest, Petersham, Massachusetts, to identify climate warming effects on forest ecosystem processes.
We characterized soil fungal communities in two replicated soil warming experiments at the Harvard Forest (Petersham, Massachusetts, USA) which have experienced above ambient soil temperatures for 5 and 20 years, and assessed their diversity and composition by metagenomic sequencing, along with soil chemistry. Several findings emerged: (1) the effect of warming on fungal community structure was dynamic through time with pronounced differences in the responses among symbiotic, saprotrophic, and pathogenic fungi. Overall, there was an initial decline in the richness and abundance of symbiotic and saprotrophic fungi with warming as compared to control plots, while pathogenic fungi remained invariant. The abundance of symbiotic fungi declined with chronic warming, whereas organic soils exposed to 20 years of warming had an increase in the abundance of yeasts and wood decomposers compared to control plots, although under similar warming conditions, there was a decline in the richness and overall abundance of plant pathogenic fungi. (2) Soil carbon concentrations in organic soils significantly declined in response to short- and long-term warming, and (3) following long-term warming, shifts in fungal relative abundance was associated with substantial changes in soil carbon storage and soil organic matter chemistry, particularly the relative abundance of lignin. Taken together, we propose that shifts in key fungal groups and fungal taxa are related to losses in soil carbon concentrations and total carbon stored in organic soils.
Publication: Pec, G. J., van Diepen, L. T. A., Knorr, M., Grandy, A. S., Melillo, J. M., DeAngelis, K. M., Blanchard, J. L., and Frey, S. D.. 2021. Fungal community response to long-term soil warming with potential implications for soil carbon dynamics. Ecosphere 12( 5):e03460. 10.1002/ecs2.3460