Linking ectomycorrhizal communities to ecosystem function and soil biogeochemical cycling

Joseph Edwards, Program in Ecology, Evolution, and Conservation Biology, University of Illinois at Urbana-Champaign, Urbana, IL, James W. Dalling, Plant Biology, University of Illinois at Urbana-Champaign, Urbana, IL, Jennifer M. Fraterrigo, Department of Natural Resources and Environmental Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, William Cyril Eddy III, Institute for Sustainability, Energy, and the Environment, University of Illinois, Urbana, IL and Wendy H. Yang, Departments of Plant Biology and Geology, University of Illinois at Urbana-Champaign, Urbana, IL

Background/Question/Methods
Ectomycorrhizal fungi (EMF) are important drivers of forest ecosystem function, critical for nutrient cycling in soils and uptake of these nutrients by their tree mutualists. While EMF-associated effects on ecosystem processes are often generalized across EMF as a unified guild based on their shared morphology, their diverse phylogenetic lineages may represent hidden functional diversity. Phylogenetic differences among EMF may promote community-driven effects on their function in soils and ecosystems that would not be captured by the traditional “ecto- vs arbuscular-mycorrhizal” dichotomy thought to shape ecosystem function. We hypothesize that, if phylogenetic relationships within EMF communities are linked with their function in the ecosystem, then soils with more closely related EMF communities will feature similar biogeochemical traits than those with more distantly related EMF communities. To test this hypothesis, we measured EMF phylogenetic biodiversity via high-throughput sequencing as well as key biogeochemical variables indicative of ecosystem function (i.e. soil enzyme activities, soil nutrient concentrations, and soil organic matter fractions) in forest soils in a “prairie grove” forest ecosystem. Within a censused forest plot, we collected soils from locations near three different genera of EMF-associating trees (Tillia, Quercus, and Carya) thought to have different litter chemistry and host-specific interactions with EMF communities.
Results/Conclusions
We found soil biogeochemical variables to diverge among the focal EMF tree genera, and that these differences may be related to differing EMF communities associating with host trees. While soil properties such as pH and soil moisture did not differ among soils collected from beneath different tree genera, soil enzyme stoichiometries differed. The potential rates of carbon : nutrient degrading enzyme activities were significantly greater beneath Tillia species than Quercus or Carya for both nitrogen (p<0.05) and phosphorus (p<0.01). Further, the relative abundance of EMF compared to other fungal functional groups was also lower under Tillia species than the other genera (p<0.05), and the most abundant EMF taxa were different among the three tree genera. Tillia species are thought to have relatively low carbon : nutrient ratio in their leaf litter compared to other EMF-associating tree species, which may cause them to select for different root microbiome communities than other broad-leaf EMF species. Microbial communities associated with Tillia species demonstrated a greater enzymatic potential for carbon degradation than communities associated with the other ectomycorrhizal trees, suggesting that functional differences among EMF communities can have an impact on biogeochemical cycling in forest ecosystems.