Soil fungal guilds as important integrators linking plant richness and carbon, nitrogen and phosphorus stocks in oasis–desert ecosystems

Plant richness strongly affects ecosystem functions, especially ecosystem carbon and nutrients stocks. However, the mechanisms underlying positive richness–stock relationships remain uncertain. Plant–fungus linkages play crucial roles in modulating stocks of terrestrial ecosystems, but empirical evidence regarding the integration of soil fungal guilds into positive richness–stock relationship under natural conditions is still lacking. Here, observations from 81 plots along a natural plant richness gradient in oasis–desert ecosystems were used to assess the role of diversity within particular soil fungal guilds in integrating the associations of plant richness with vegetation and topsoil (0–30 cm) carbon (C), nitrogen (N) and phosphorus (P) stocks. We observed that plant richness has positive associations with vegetation and topsoil C, N and P stocks in oases and deserts. Mycorrhizal fungal abundance showed consistent and positive associations with plant richness and vegetation and topsoil C, N and P stocks in the oasis after accounting for groundwater, soil factors and soil enzyme activities, whereas similar patterns were found for saprotrophic fungal abundance in the desert. We further demonstrated mycorrhizal and saprotrophic fungal abundance as important integrators of the positive richness–stock relationships in oases and deserts, respectively. Moreover, guild-level fungal abundance surpasses whole fungal community attributes in linking plant richness and stocks in oases and deserts. The present study provides real-world evidence supporting the crucial roles of fungal functional groups diversity in integrating the positive associations of plant diversity with ecosystem C and nutrients stocks in oasis–desert ecosystems. By unravelling the importance of fungi for ecosystem C and nutrients stocks, our work emphasises that ecosystem restoration should consider not only plant richness to enhance ecosystem C and nutrients stocks but also the roles of key fungal groups.