Decay of fallen wood and elevation affects soil fungal community assembly and indirectly controls community diversity

Fallen wood has a pivotal role in the forest ecosystem and acts as an important intermediary for material cycling and energy flow between vegetation and soil. A keystone of the forest ecosystem is the soil fungal community which performs a crucial role in regulating the internal functions of the system. Nonetheless, the characteristics of soil fungal community diversity and the process of community assembly beneath fallen wood remain unclear. Here We investigated two subtropical forests at different elevations, and selected three fallen wood of different decay classes and a control soil without fallen wood in each stand. The soil underneath the fallen wood was collected for analysis to explore the effects of decay on soil fungal diversity and community assembly processes. The 18S rRNA amplicon sequencing was used to determine fungal diversity and calculate normalized stochasticity ratios (NST), whilst the underlying soil ecological factors were measured to predict the possible drivers of fungal diversity along with the driving mechanisms. The results revealed that elevation and fallen wood decay had a significant interactive effect on soil fungal alpha diversity as well as beta diversity. Outcomes of tNST (taxonomic Normalized Stochasticity Ratio) suggested that fallen wood decay at high-elevation made stochastic processes progressively more important in the assembly of soil fungal communities, while the opposite occurred at low-elevation, yet the results calculated by the pNST (Phylogenetic Normalized Stochasticity) method tended to indicate a predominance of stochastic processes in both two elevations. Fungal diversity was strongly positively correlated with NST values, but soil ecological factors were only strongly associated with NST values. The partial least squares path model (PLS-PM) further indicated that elevation and fallen wood decay did not directly regulate changes in fungal community diversity, but indirectly controlled fungal community assembly processes by affecting soil ecological factors, anon varied fungal diversity as well as community structure. This work will generate fresh insight into the patterns of soil fungal diversity and community assembly processes in forest ecosystems.