Land use driven change in soil organic carbon affects soil microbial community assembly in the riparian of Three Gorges Reservoir Region

After decades of anti-seasonal water fluctuation in the Three Gorges Reservoir (TGR), a distinctive riparian zone had been formed and played critical roles on soil biogeochemistry cycling, substance exchange and soil microbial functions. However, the effect of land use on terrestrial ecological processes and soil microbial community assembly in riparian zone was still imprecise. This study focused on the relationship of soil properties and microbial communities in paddy and dryland soils of a typical riparian zone in the TGR. The results indicated a higher level of accumulation of total organic carbon (TOC) in paddy soil (14.88–20.29 g kg −1 ) than that in dryland soil (7.59–16.20 g kg −1 ). The riparian soil was slightly polluted by cadmium and phthalate acid esters with an average concentration of 0.19 mg kg −1 and 6.45 mg kg −1 , which may be from agricultural sources, posing a potential health risk. Based on 16S rRNA sequencing analysis, there was a higher microbial diversity in paddy soils than dryland soils, and Acidobacteriaceae and Anaerolineaceae represented the dominant taxa in dryland and paddy soils, respectively. Furthermore, the results of redundancy analysis and structural equation modeling showed that land use driven change in soil organic carbon affected the fate of soil pollutants, and constructed soil microbial communities in the riparian zone of TGR. Null model revealed that homogeneous selection explained about 76.36% and 53.33% microbial community assembly, followed by dispersal limitation (14.54% and 37.50%) in dryland and paddy soil. In consequence, a strong effect of environmental filtering was observed on arable soil microbial community structure with different land use in the riparian zone of TGR, and TOC was the key regulator. • Soil microbial communities were clearly distinguished by land use. • TOC was a major determinant of soil microbial community assembly in TGR. • Stochastic and deterministic process controlled the community assembly.