Interactions Between Fungal Communities and Localized Conservative N Cycling in Mixed Mycorrhizal Tropical Forests

Abstract Background and aims Ectomycorrhizal (ECM) trees and associated fungal communities can interact with underlying nutrient dynamics to suppress carbon (C) and nitrogen (N) cycling locally. Specifically, N availability may dictate interactions between ECM and saprotrophic fungi and belowground C allocation by ECM trees, potentially determining the potential of fungal communities to suppress N cycling beneath ECM trees. However, these mechanisms have largely been tested in temperate and boreal systems where underlying N limitation is common.Methods Here, we quantified fungal community metrics and soil chemical properties in a long-term N addition experiment located in a lower montane tropical forest to assess the role of fungal communities in driving conservative N cycling beneath ECM trees within mixed ECM-AM stands where N is not necessarily limiting.Results We found that natural abundance N isotopes correlated with a shift in fungal community composition between control and N addition plots, suggesting that N availability may affect belowground C allocation to increase colonization by ECM fungi that are a larger C investment and have a greater potential to interact with soil N cycling. However, we found no effect of N addition on the distribution of ECM and saprotrophic fungal guilds through the soil profile, suggesting that abiotic and biotic conditions which promote rapid N cycling may decrease interguild competition in a tropical montane forest.Conclusions Overall, local scale nutrient limitation dynamics driven by interactions between ECM host trees and underlying fungal communities may be partially mediated by ecosystem scale nutrient cycling dynamics.