Soil microbial communities acted as the most active component in the riparian biota, playing a critical role in driving carbon cycling. The frequency of periodic flooding in riparian zones poses significant driving forces for the structure and function of soil microbial communities. Yet, whether such events can induce the change in microbial carbon metabolism efficiency is not fully reported, especially in large reservoirs that experienced non-seasonal water level fluctuations (WLFs). Here, high-throughput sequencing technology and the ¹⁸O-H₂O cultivation method were applied to investigate soil microbial community and carbon metabolism in a tributary riparian zone in China’s Three Gorges Reservoir which experienced large WLFs between 145 m and 175 m above the sea level. Three elevations of the riparian zone, i.e., 155 m, 165 m, and 170 m, were selected as treatment of different flooding intensities. As the frequency of flooding decreases, soil enzyme activity exhibits a trend of initial decrease followed by an increase, while soil water content and the complexity of microbial co-occurrence networks gradually decrease, and community stability strengthens. Significant differences are observed in microbial community structure and diversity among different flood-intensity treatments. Overall, the assembly mechanism of microbial communities is primarily governed by homogenizing dispersion in stochastic processes. Decreased extracellular enzyme activities contribute to increased microbial carbon use efficiency, and decreased metabolic quotient, thereby promoting soil carbon storage. This work enhances our understanding of the response and mechanisms of soil microbial communities to periodic flooding, providing a theoretical foundation for soil carbon cycling processes in the riparian zone.
 

周期性淹水,河岸带,微生物,碳利用效率