Response of soil bacterial community and geochemical parameters to cyclic groundwater‐level oscillations in laboratory columns

Groundwater-level oscillations change geochemical conditions, C cycling processes, and bacterial community composition, and these changes may vary vertically with depth in a soil. In this study, soil column experiments were conducted to explore variations in soil bacterial community composition and its associated geochemical parameters to rapid short-term cyclic groundwater-level oscillations driven by natural fluctuations (NF) and rainfall infiltration (RI), and the results are compared with a quasistatic (QS) column. Water saturation patterns in vadose and oscillated zones, and O-2 level patterns, soil total organic C (TOC) removal rates, and soil bacterial community composition in vadose, oscillated, and saturated zones were evaluated. Results showed that water saturation and O-2 level oscillated with groundwater level in NF and RI columns. Total organic C removal rates in RI column were the highest across vadose (similar to 38.4%), oscillated (similar to 35.8%), and saturated (similar to 35.2%) zones. Deltaproteobacteria, which were significantly correlated with TOC removal (p < .05), were found in higher abundance in the vadose and oscillated zones of the RI column than in the QS and NF columns. Soil bacterial community structure was dynamic at the class level due to water saturation, O-2 level, and TOC removal. Total organic C removal was the driver to separate the distribution of bacterial community structure in the vadose and oscillated zones of the RI column from those of the QS and NF columns. This study suggests that RI induced rapid, short-term, cyclic, groundwater-level oscillations could significantly influence both the soil C cycle and bacterial community structure in the vadose and oscillated zones.