Land-Use Type Affects Soil Microbial Community Assembly Process and Inter-Kingdom Co-Occurrence Pattern in a Floodplain Ecosystem

The floodplain ecosystem is crucial for facilitating or regulating regional ecological functions. The intensified use of floodplain may significantly influence the soil's potential to handle ecosystem services by changing key biotic groups such as soil microbes. However, little is known about the response of soil microbial communities to land-use types in the floodplain. This study investigated the community assembly process and co-occurrence network pattern of bacteria, fungi, and protists under three land-use types: tender floodplain, farmland, and abandoned farmland. We found that land-use types had considerable changes in soil fertility and a decline in soil fertility associated with abandoned farmland. Compared with microbial diversity, the composition and structure of the microbial community were more susceptible to land-use types. The increasing divergence of the soil fertility index increased the variations in community structure. Stochastic processes dominated the bacterial and fungal community assembly in tender floodplains and abandoned cropland, while deterministic processes dominated farmland. Stochastic processes dominated protist community assembly in the three land-use types. In particular, the contribution of deterministic processes to bacterial, fungal, and protist communities on farmland was higher than that in a tender floodplain and abandoned farmland. Bacteria dominated the co-occurrence network. The tender floodplain had the most stable microbial network among the three land-use types, whereas abandoned farmland had the least robust microbial network. Our results indicated that land-use types might strongly change soil microbial assembly processes and co-occurrence network patterns, which may provide a scientific foundation for sustainable management and conservation in floodplain ecosystems