Aboveground vegetation and soil physicochemical properties jointly drive the shift of soil microbial community during subalpine secondary succession in southwest China

Based on long-term ecological research, microorganisms are sensitive to environmental changes in the process of ecosystem succession. However, few works have focused on the response of different groups of soil microorganisms to subalpine secondary succession and the driving forces behind the stepwise community development. To explore the changes in the microbial community structure and the driving mechanisms, we selected three replicated secondary succession gradients consisting of grass, shrub, different secondary forests (picea, pine and birch) and primary forest in a subalpine area in southwestern China. A high-throughput sequencing method was used to compare differences in the soil fungal and bacterial community structures. In combination with aboveground plant diversity and soil properties, the different mechanisms controlling the soil microbial community were revealed by the Mantel test. A two-way correlation network was also used to explore the connections among stages. The results show that the change in bacterial and fungal community structure was obvious, and these changes of bacteria were significantly correlated with soil acid phosphatase, LAP, soil moisture and aboveground vegetation communities during succession development in subalpine forests. Moreover, the fungal community was related to soil organic carbon, nitrogen, vegetation diversity, abundance and community structure. We also found that different dominant fungi play crucial roles in the succession sequence, and the relationship between soil microbes and vegetation is gradually simplified and stabilized. Our work suggests that both the relatively stable bacterial communities and the significantly changing fungal communities are notably associated with abiotic and biotic factors in secondary succession. As the ecosystem evolves, the dominant fungi obviously respond to succession and can successively establish close relationships with plants. Consequently, our results have important implications for understanding the driving mechanisms that control the soil microbial community during subalpine forest secondary succession.