Response of bacterial communities and soil chemistry to flood durations and recovery phases.

ABSTRACT

Flooding profoundly impacts soil bacterial communities; however, the underlying mechanisms remain poorly understood. This study investigated how flooding (3, 8, and 16 days) and post-flooding (immediately and 2, 5, and 30 days) durations affect soil physicochemical properties, bacterial communities, and their interactions-crucial factors in floodplain nutrient and carbon cycling. The results showed that bacteria constituted 99.9% of the total microbial composition, while archaea, contributing only 0.1%, had a negligible impact on soil traits. At 2-5 days after flooding (DAF), elevated soil electrical conductivity (EC) and pH enhanced soil bacterial abundance and activity, leading to increased water-extractable dissolved organic carbon (DOC), water-extractable total dissolved nitrogen, and biological production (BIX), accompanied by the degradation of soil organic matter (SOM) and aromatic compounds (SUVA254). These changes indicated robust interactions between soil bacterial communities and physicochemical properties affected by flooding events. However, these relationships weakened at 30 DAF, suggesting potential transitions from anaerobic to aerobic conditions in post-flooding soils after 5 DAF. Structural equation modelling indicated that an extended post-flooding duration increased BIX, accompanied by SOM and DOC degradation, providing nutrients and energy to soil microbes and consequently leading to increased bacterial diversity. This study underscores the significant impact of flooding and post-flooding durations on soil bacterial community composition and diversity, mediated by changes in EC, pH, SOM, and DOM, potentially influencing nutrient cycling in floodplains.