Characteristics of Spatiotemporal Distribution of Microbial Communities in the Riparian Zone of the Three Gorges Reservoir Area

To investigate the impact of periodic water-level fluctuations on soil microbial community structure in the riparian zone of the Three Gorges Reservoir Area, this study focused on the riparian zone at Zhangjiawan near the dam. Surface soil samples (0–20 cm) were collected in spring, summer, and autumn from three elevation gradients: below 160 m, 160–170 m, and above 170 m. Phospholipid fatty acid (PLFA) was employed to characterize the microbial community structure. The results indicated that microbial community distribution was significantly influenced by both elevation and season, with bacteria dominating community variations. In terms of elevation, the total microbial biomass and bacterial abundance were highest at the 160–170 m gradient, followed by the area above 170 m, and lowest below 160 m. Season and elevation exhibited a significant interactive effect on fungi. Seasonal patterns showed that total microbial biomass and bacterial abundance peaked in summer, whereas fungal abundance and the fungi-to-bacteria ratio were higher in autumn. In contrast, actinobacterial abundance remained stable across seasons. Soil organic carbon (SOC; 60.3%) was identified as the predominant environmental factor influencing microbial community structure, followed by total nitrogen (TN; 13.9%) and pH (2.4%). SOC was identified as the key driver of microbial community dynamics. These findings clarify the respective roles of water level fluctuation, seasonal variation, and environmental factors in shaping riparian microbial communities, providing critical baseline data and theoretical support for ecological protection and scientific management of the Three Gorges Reservoir Area.