Abstract: Community structure and co-occurrence relationships of soil microorganisms were studied using Illumina high-throughput sequencing technology to better understand restoration characteristics and assembly mechanisms of soil microbial communities during natural restoration of forest. Tropical rainforests with naturally restored for 40-60 years after three types of disturbance (slash and burn, clear cutting, and selective cutting) were compared with old-growth forests. A Null model was used to quantify the relative contributions of deterministic processes and stochastic processes in microbial community assembly. Results showed that soil physicochemical properties (total nitrogen, hydrolysable nitrogen, and available potassium) in the slash and burn forests were not significantly different from that in the old-growth forests. Plant diversity was significantly lower than old-growth forests (P<0.05). Soil bacterial diversity was not significantly different from that of old-growth forests, but soil fungi richness was significantly lower (P<0.05). Most soil physicochemical properties, including total nitrogen, available phosphorus and available potassium, as well as plant diversity, were significantly higher after clear cutting and selective cutting than that in old-growth forests (P<0.05). There was no significant difference in soil microbial diversity. Soil microbial community structure of forests from the three different disturbance types was significantly different from that of old-growth forests (P<0.05). Results of ecological network analysis showed that slash and burn and clear cutting disturbances reduced network complexity of soil microorganisms, while selective cutting increased the complexity. Network structure (total nodes, total links and modularity) of soil bacteria was greater than that of soil fungi. The Null model analysis showed that the relative contribution of stochastic processes (bacteria: 54.76%-66.58%; fungi: 87.62%-93.57%) was higher than deterministic processes (bacteria: 33.42%-45.24%; fungi: 6.73%-12.38%). The slash and burn disturbance had the greatest impact on soil microbial diversity and community structure. After a long-term natural recovery, soil microbial diversity did improve, with greater recovery for bacteria than for fungi, but with large differences in soil microbial community structure and relationships. Our study elucidated microbial community structure and assembly processes in forest soils affected by different disturbances, which is important for predicting ecosystem function of soil microorganisms and their responses to environmental changes.

Key words: soil microorganisms, community recovery, disturbance type, ecological network, assembly mechanism.