Tracking the changes of wetland soil bacterial community and metabolic potentials under drought and flooding conditions in experimental microcosms

Wetland soils may face more severe water stress under future climate change. Our aim was to assess the change characteristics of wetland soil bacterial community and metabolic potentials under drought and flood conditions. Wetland soil was incubated under five different water environments (including constant moisture at 30%, natural air-dried, and 3 types of flooding depths) by conducting experimental microcosms. After 1, 21, and 132 days of incubation, the soil bacterial community structure and metabolic potential were examined by the 16S rRNA gene sequencing and Biolog-Ecoplates method, respectively. The results showed that Actinobacteria and Firmicutes were significantly enriched under drought and flooding treatments, respectively. Compared to flooding, drought decreased soil microbial biomass and carbon metabolism more severely. However, the depth of flooding did not significantly change bacterial community composition and carbon metabolism. In addition, the responses of soil metabolic functions to drought were more sensitive than the change of bacterial community composition. When the wetland soil faced water stress (drought and flooding), its metabolic functions showed close correlations with bacterial community composition and were negatively affected by most of environmental factors (such as pH, NO3-N, and NH4-N). The results indicate that the drying condition is more severe and rapid than flooding in threatening soil microbial metabolic activity. In addition, the depth of flooding does not significantly change bacterial community composition and carbon metabolism.