Effects of water flow conditions on soil properties and microbial communities in the lower Heihe river Basin, Northwest China.

BACKGROUND: Effective hydrological management in arid ecosystems requires a comprehensive understanding of how water flow conditions influence biota and ecosystem processes. However, the responses of soil microbial communities remain poorly understood. This study aims to evaluate whether, and to what extent, a 20-year difference in flow regimes affects soil microbial diversity, composition, and function. The composition of the soil microbial community and the factors shaping it were investigated in two arid riparian zones (East River and West River) of the lower Heihe River Basin using 16 S rRNA amplicon high-throughput sequencing. RESULTS: The dominant phyla of the bacterial, fungal, and archaeal communities were Proteobacteria, Ascomycota, and Euryarchaeota, respectively. Co-occurrence network analysis revealed greater network connectivity and stability in the West River, suggesting enhanced mutualistic interactions and physiological acclimation strategies in response to low-flow conditions. Microbial-soil correlations varied with flow condition: bacterial and fungal communities under high-flow conditions were associated with bulk density and available nitrogen, whereas low-flow communities were more influenced by available potassium. High-flow conditions also strengthened the correlation between microbial communities and nitrogen-related functions. Functional prediction showed that chemoheterotrophy was the dominant bacterial function, and bacterial and archaeal communities were partially involved in the nitrogen cycle. CONCLUSIONS: Changes in flow regimes slightly modulated microbial community composition and diversity. However, microbial functions appeared to respond more strongly to hydrological factors than microbial diversity. Thus, alterations in microbial structure and function were jointly influenced by hydrological conditions and the availability of nutrients in arid riparian zones.