Dynamics of microbial biomass and community composition after short-term water status change in Chinese paddy soils

Paddy soil experiences repeated anaerobic and aerobic changes during rice growth, the dramatic dynamics of soil water status accompanied by changes in redox condition and O₂ availability. However, the effect of rapid water status change on soil microbial biomass and community composition is not well explored. Here, we present a comprehensive study focusing on the short-term water status change in 13 Chinese paddy soils. In order to gain a reliable way to determine soil microbial biomass carbon (MBC) in flooded or water-saturated soils, we also evaluated two different procedures (nitrogen bubbled and 100 °C water bath) to remove chloroform in extracts during the fumigation process. Compared to non-flooded paddy soils, the flooded paddy soils tended to have a lower microbial biomass, and this was much clearer using adenosine 5'-triphosphate (ATP) and phospholipid fatty acid (PLFA) analysis compared to biomass measured by the fumigation method. Fungal biomass, which was indicated by both ergosterol and the PLFA 18:2ω6,9c, also decreased after short-term flooding. Changes in soil microbial community composition (determined by PLFA biomarkers) were observed after short-term flooding, but the extent varied between soils. This study indicates that the dynamics of short-term water status altered the soil microbial biomass (ATP, MBC, and total PLFA) and community composition. Finally, our results suggested that liquid fumigation combined with the nitrogen-bubbled method is the best choice for analyzing MBC concentrations in water-saturated soils.