Functional complementarity of abundant and rare taxa mediates soil carbon sequestration during subtropical forest...

Forest restoration drives profound reorganization of soil microbial communities, yet how abundant versus rare taxa differentially govern ecosystem recovery through community assembly and functional complementarity remains poorly understood. Here, we integrated null-model analysis, co-occurrence networks, and environmental threshold modeling across a subtropical forest chronosequence (39-180 years; Pinus massoniana to Castanopsis climax) to reveal taxon-specific assembly processes and their implications for carbon sequestration. Our results showed that rare taxa (92.8-94.4% OTUs) exhibited increased α-diversity and a stronger influence of deterministic assembly (homogeneous selection) with increasing restoration age, driven by soil dissolved organic carbon. Conversely, stochastic processes dominated the assembly of abundant taxa (4.3-6.3% OTUs), maintaining broader environmental thresholds. Microbial network patterns further demonstrated that keystone taxa in early restoration stages were predominantly abundant taxa (e.g., Chloroflexi, Planctomycetota), maintaining network centrality and stability, whereas with advancing restoration, rare taxa increasingly contributed to network modular integration and overall stability. Functionally, abundant taxa sustained resource acquisition and environmental responsiveness, whereas rare taxa exhibit higher carbon-related function potential such as Carbon metabolism and Glycolysis and Gluconeogenesis, indicating distinct ecological roles. Structural equation modeling further revealed stronger associations between rare taxa and soil organic carbon compared with abundant taxa. These results provide new insights into the microbial community composition in restored ecosystems and highlight the critical role of functional complementarity between abundant and rare taxa in jointly maintaining microbial diversity and network structural stability during forest restoration. We demonstrate that managing microbial complementarity can amplify carbon sequestration by 22-40% in restored forests, thereby providing a microbial toolkit for achieving Natural Climate Solutions.