Rare bacterial taxa drive the ecosystem multifunctionality in lake water-level-fluctuating zone during seasonal water level fluctuations

[Display omitted] •Bacterial diversity was positively correlated with multifunctionality in WLFZ;•Diversity of always rare taxa affect multifunctionality in drought state;•Diversity of conditionally rare taxa affect multifunctionality in flooding state;•Rare bacterial sub-community drive multifunctionality in WLFZ; Complex microbial community plays a crucial role in driving soil ecosystem multifunctionality. Water-level-fluctuating zone (WLFZ) of lakes serves as vital transitional areas between land and water, exhibiting crucial ecological functions. However, the relationship between soil moisture-sensitive bacterial communities and ecosystem multifunctionality remains poorly understood. In this study, we conducted a two-year seasonal field survey in the WLFZ of one large flooding lake. By using amplicon sequencing, we explored the changing characteristics of soil bacterial communities during water level fluctuations and their driving role in ecosystem multifunctionality. A simultaneous decrease in soil bacterial diversity and ecosystem multifunctionality was observed as the soil transitioned from drought to flooding states. Soil bacterial diversity was positively correlated with ecosystem multifunctionality, and rare bacterial sub-communities showed a higher correlation with multifunctionality than the overall bacterial community. Random forest regression analysis demonstrated that rare bacterial sub-communities were the optimal predictor variable for ecosystem multifunctionality in the WLFZ. Additionally, Actinobacteriota and Methylomirabilota held significance in predicting multifunctionality under drought and flooding states, respectively. This study highlighted the predominant role of soil rare bacterial sub-communities in driving ecosystem functionality in the WLFZ.