[Impact of forest succession on soil microorganisms and soil multifunctionality in subtropical forests]

This study focused on the early-, mid- and late-stage of subtropical forests, as represented by Cunninghamia lanceolata plantations (with stand ages of 5, 10, and 20 years), the mixed coniferous-broadleaf forests, and broadleaf forests, respectively. Using real-time fluorescence quantitative PCR and high-throughput sequencing techniques, we investigated the variations of rare and dominant soil microbial groups and soil multifunctionality across the succession stages. The results showed that forest succession altered the composition and structure of rare and dominant groups of microbial communities, significantly increased the abundance of dominant and rare soil microorganisms, but reduced their diversity. As succession progressed, the relative abundance of the rare bacterial phylum Planctomycetes significantly increased, the relative abundances of the phyla Bacteroidota, Chloroflexota, Gemmatimonadota, and Proteobacteria significantly decreased, while the relative abundance of the dominant fungal phylum Zygomycota significantly increased. With forest succession, soil multifunctionality significantly improved. Soil multifunctionality indices increased by 51.4%, 67.2%, 80.1%, and 69.2% in the 10-year-old C. lanceolata plantation, the 20-year-old C. lanceolata plantation, coniferous-broadleaved mixed forests, and broad-leaved forests respectively, compared to 5-year-old C. lanceolata plantation. Soil multifunctionality was significantly correlated with the abundance and diversity of dominant microorganisms but not with rare microorganisms, suggesting that dominant soil microorganism species might contribute more to soil multifunctionality than rare species. Soil nutrient content was identified as a key factor influencing rare and dominant microbial groups. Forest succession significantly enhanced soil multifunctionality, and dominant species may play a more critical role in maintaining soil multifunctionality compared to rare species.