Changes in Soil Microbial Diversity Across Different Forest Successional Stages: A Meta-Analysis of Chinese Forest Ecosystems

Using meta-analysis of 479 sites across Chinese forests from 136 publications, we quantified changes in soil microbial diversity across forest successional stages and compared patterns between plantation and natural secondary forests. Our systematic review included 136 publications (92 in Chinese, 44 in English), spanning tropical to cold temperate climate zones from 1995–2025. Microbial α-diversity exhibited a significant U-shaped pattern across successional stages: early succession (0–15 years) and mature forests (>50 years) had higher Shannon diversity (4.56 ± 0.34 and 4.72 ± 0.41, respectively) than middle-aged forests (16–50 years, 4.18 ± 0.27; standardized mean difference = 0.54, 95% CI: 0.39–0.69, p < 0.01). Response patterns differed significantly among microbial groups (Q = 8.74, p = 0.013), with fungi showing the strongest successional responses (SMD = 0.61, 95% CI: 0.43–0.79), followed by bacteria (SMD = 0.49, 95% CI: 0.32–0.66) and actinomycetes (SMD = 0.42, 95% CI: 0.24–0.60). Natural secondary forests consistently supported higher microbial diversity than plantations (SMD = 0.42, 95% CI: 0.28–0.56), particularly for fungal communities (SMD = 0.47, 95% CI: 0.31–0.63). The climate zone significantly moderated diversity–succession relationships, with subtropical regions showing the largest changes (ΔShannon = 0.68 ± 0.07) compared to temperate (ΔShannon = 0.42 ± 0.05) and tropical regions (ΔShannon = 0.54 ± 0.06). Meta-analytic structural equation modeling revealed that soil organic carbon (path coefficient β = 0.68, p < 0.001), total nitrogen (β = 0.43, p < 0.001), and pH (β = −0.35, p < 0.01) were key mediators connecting succession stage with microbial diversity. Despite substantial between-study heterogeneity (I2 = 83.6%), a publication bias was not detected (Egger’s test, p = 0.347). These findings provide the first comprehensive quantification of microbial diversity patterns during forest succession in China, with important implications for forest management and ecological restoration strategies targeting microbial conservation.