A global meta-analysis reveals coupled biogeochemical and microbial successional trajectories in forest soils

Forest succession fundamentally reshapes soil biogeochemistry and the resident microbial communities, yet a synthesis of global response patterns has been hindered by methodological inconsistencies and conflicting regional findings. Through a meta-analysis of studies published from 2015 to 2025, we evaluated global patterns in soil properties, microbial communities across forest successional stages. We found that soil organic carbon (SOC) and total nitrogen (TN) increased significantly from early to late successional, while soil pH declined. Microbial α-diversity increased sharply from early to mid-succession before slightly declining in late stages. Structural equation modeling (SEM) indicated that TN is the primary positive driver of both bacterial and fungal diversity and community composition, whereas SOC, pH, and climate factors exhibited weaker or stage-specific effects. Community composition also shifts systematically from a predominance of fast-growing, copiotrophic taxa (e.g., Proteobacteria, Ascomycota) in early stages to slow-growing, oligotrophic specialists (e.g., Actinobacteriota, Basidiomycota) in late stages. Bacterial diversity was more sensitive to climatic variables (precipitation, temperature), while fungal communities were more strongly governed by soil nutrient availability. This synthesis reconciles disparate findings by demonstrating that forest succession drives predictable, coupled trajectories in soil nutrients and microbial community composition. Our results provide a mechanistic framework for understanding belowground ecosystem development and its functional implications for forest biogeochemistry.