Responses of Bacterial Community and N-Cycling Functions Stability to Different Wetting-Drying Alternation Frequencies in a Riparian Zone

Abstract

Wetting-drying alternation of the soil is one of the key characteristics of riparian zones shaped by dam construction, profoundly impacting the soil microenvironment that determines the microbial community. Knowledge concerning the stability of the soil bacterial community and N-cycling functions in response to different wetting-drying alternation frequencies remains unclear. In this study, samples were taken from a riparian zone in the Three Gorges Reservoir (TGR) and an incubation experiment was conducted including four treatments: constant flooding (W), varied wetting-drying alternation frequencies (WD1 and WD2), and constant drying (D) (simulating water level of 145 m, 155 m, 165 m, and 175 m in a riparian zone respectively). The results revealed that there was no significant difference in either the α-diversity or β-diversity among the four treatments. Following the WD1 and WD2 treatments, the relative abundances of Proteobacteria increased, while those of Chloroflexi and Acidobacteriota decreased compared to the W treatment. However, the stability of the bacterial community was not affected by wetting-drying alternation. Relative to the W treatment, the resistance of N-cycling functions was decreased significantly following the WD1 treatment and showed no significant change after the WD2 treatment. Random forest analysis showed that the resistances of the nirS and hzo genes were significant contributors to the resistance of N-cycling functions. In conclusion, wetting-drying alternation had no influence on the stability of the bacterial community, however, the stability of N-cycling functions was higher following the WD2 treatment, which was largely underpinned by higher resistance of nirS and hzo genes compared to the WD1 treatment. This study reveals the response of the bacterial community and N-cycling functions stability to different frequencies of wetting-drying alternation and provides a new perspective for investigating the impacts of wetting-drying alternation on soil microbes.

Keywords: Bacterial community, N-cycling functions, Wetting-drying alternation, Stability, Riparian zone, Water level fluctuations