Assembly processes and networks of soil microbial communities along karst forest succession

Abstract

Understanding the assembly processes of soil microbial communities as secondary succession proceeds offers a critical insight into ecosystem recovery after disturbance. However, a comprehensive understanding of which ecological processes govern the assembly remains elusive. In this study, soil samples were sampled across four seasons (i.e., spring, summer, autumn, and winter) from various forest succession including shrubland, secondary forest, and primary forest, within a karst region in southwestern of China. The assembly of microbial communities was analyzed using the method of the null model, coupled with measurements of environmental variability. The results demonstrate that soil bacterial assembly is primarily dominated by the deterministic processes with their relative influence increases as karst forest proceeds; while soil fungal assembly is dominated by the stochastic processes, and the relative significance of stochasticity peaks in the secondary forest. Moreover, both soil bacterial and fungal communities’ co-occurrence networks intensifies as forest succession. The shift in the balance between deterministic and stochastic across successional stages is predicted by factors such as plant DBH and soil nutrient availability. Specially, soil nitrate nitrogen (NO₃^–-N), along with plant diameter at breast height (DBH), available potassium (AK), available phosphorus (AP), and total phosphorus (TP), emerged as crucial determinants of soil microbial assembly as karst forest succeeds. Overall, our study provides the evidence that the bacterial and fungal communities’ assembly vary within and across forest succession, and highlights the importance of plant properties and soil micro-environment for these community assembly in karst soil.