Disentangling mechanisms that mediate soil fungal α and β diversity during forest secondary succession

Abstract

Understanding the mechanisms controlling community diversity is a central, topic in ecology, particularly in microbial ecology. Although species pools and local assembly processes are believed to play non‐negligible roles in shaping the within‐community (α) and among‐community (β) diversity of microbial communities, their relative importance as succession progresses remains elusive. Moreover, the roles of both mechanisms on diversity might be strikingly different depending on whether saturation is considered or not, yet this issue is far less appreciated. To investigate the mechanisms underlying soil fungal α and β diversity during secondary succession, soil samples were collected from six different successional chronosequences including 293 plots across different climatic zones. We found that in all chronosequences, increases in α diversity tracked increases in species pool size, showing a linear unsaturated relationship, despite β diversity not always co‐varied with species pool size. After correcting for differences in species pools, environmental selection appeared to explain variation in β diversity rather than variation in α diversity. Further piecewise structural equation modeling demonstrated that the species pool was more important in α diversity change than environmental selection in most of the cases, whereas the importance of heterogeneous selection outweighed species pool in shaping β diversity. Overall, these findings represent one of the first to demonstrate that most local fungal communities might be unsaturated, where the relative importance of species pool and environmental selection for variations in α and β diversity during secondary succession differs markedly. Considering the mechanisms controlling diversity will be distinctly different under unsaturation or saturation, we set up an extended conceptual model combined with saturation theory to broaden the perspective to comprehensively understand mechanisms causing biodiversity change during secondary succession in unsaturated/saturated communities, intending to enhance our ability to predict soil fungal diversity in the future.