Trends in soil microbial communities during secondary succession

Succession, a central theme throughout the history of ecology, has been well studied predominantly in plant communities, but the general trends in soil microbial communities during succession remain unclear. Here, we compiled a comprehensive data set of 85 age sequences worldwide with the aims to (1) examine the trends in soil microbial composition, bioenergetics, and activity during secondary succession, and (2) explore their coordinating changes with soil properties. The results showed that the fungi to bacteria ratio (fungi:bacteria) increased, while the microbial respiration per unit biomass carbon (R/C_mic) decreased as the succession proceeds. Secondary succession had the rising trends in microbial biomass carbon to soil carbon ratio (C_mic/C_soil) and microbial biomass nitrogen to soil nitrogen ratio (N_mic/N_soil). These successional trends in microbes were coincident with the macro-ecological succession theory in plants and animals. Specifically, early successional stages tended to be dominated by r-strategists (bacteria) that had higher R/C_mic and lower C_mic/C_soil and N_mic/N_soil, whereas late successional stages tended to be dominated by K-strategists (fungi) that behaved oppositely. The soil C to N ratio (C:N_soil) increased significantly with the successional stage, with a fast increasing C:N_soil ratio being accompanied by a fast increase of fungi:bacteria, a slow decrease of R/C_mic, and a slow increase of C_mic/C_soil. This result suggests that the stoichiometry theory may provide a feasible approach to explain the divergent successional trends in microbial communities. In conclusion, our global synthesis highlights the application of the existing macro-ecological theory to soil microbial ecology studies.