Stand ages and soil compartments jointly shape ecosystem multifunctionality via changes in bacterial and fungal diversity and community composition

Background: Soil microbes play critical roles in supporting multiple ecosystem functions in forests. Their community characteristics are strongly influenced by the soil compartments they occupy (e.g., rhizosphere and bulk soils) as well as stand ages during plantation restoration. However, little is known about whether the effects of microbial communities on soil multifunctionality differ between soil compartments and how these effects are influenced by stand stages. Methods: We investigated the diversity and community composition of bacteria and fungi in rhizosphere and bulk soils of Chinese fir (Cunninghamia lanceolata) plantations across different stand ages (6, 18, and 42 years), focusing on the relationships between microbial communities and soil multifunctionality, as well as the environmental dependence of these relationships. Result: We found that rhizosphere soil multifunctionality was significantly higher than in bulk soil in both young and mature plantations. Soil multifunctionality initially decreased and then increased with stand ages, but did not return to the level observed in the young plantation. Stand ages and soil compartments significantly influenced soil multifunctionality by regulating bacterial and fungal β-diversity rather than α-diversity. Most bacterial and fungal taxa exhibited positive correlations with ecosystem multifunctionality. The structural equation model revealed that the effects of fungal diversity on soil multifunctionality were much stronger than those of bacterial diversity. Conclusion: These findings enhance our understanding of the mechanisms by which soil microbial diversity and community composition mediate ecosystem functions in plantation forests and provide a valuable reference for scientific forest management and maintaining the stability of ecosystem multifunctionality.