Fungi perform keystone roles in terrestrial nutrient cycles through uptake of mineral nutrients by mycorrhizae and return of elements by saprotrophic decomposition of detritus. Linking these ecological roles to specific microbial organisms is necessary to refine understanding of biogeochemical cycling and fungal ecophysiology. We analyzed published and novel fungal nitrogen (δ15N) and carbon (δ13C) stable isotope values to test if global patterns follow theoretical predictions and could be used to reliably identify ecological roles of macrofungi. Correlation analyses with climate and latitude indicated that systematic variation among both isotopes required site normalization prior to conducting discriminant multivariate analyses.
Results/Conclusions
A discriminant multivariate analysis verified collector based categorization of ectomycorrhizal (ECM) and saprotrophic (SAP) fungi in 92.5% of species and predicted probabilistic classifications for fungi of unknown trophic status despite significant background isotope variation. Fungal δ13C was best correlated with latitude (ECM r2=0.54, SAP r2=0.70) and mean annual temperature (ECM r2=0.26, SAP r2=0.66) whereas fungal δ15N was correlated with mean annual temperature in ECM fungi only (r2=0.28). The difference between ECM and SAP (ΔECM-SAP) δ15N and δ13C values were of comparable magnitudes (6‰ and -2.2‰) across sites despite broad ranges in climate and soil type. The consistent isotopic divide among trophic groups suggests that fungal physiology appears to exert greater influence on sporocarp δ15N than source-N and that C-source (photosynthate in ECM and detritus in SAP) isotope effects are similar across the globe.
