Responses of microbial respiration rate and active bacterial communities to antecedent soil moisture on the Loess Plateau

Abstract

Previous studies on microbial respiration responses to soil moisture have primarily focused on the influence of current moisture conditions, largely overlooking the role of antecedent soil moisture and its effects on the soil carbon (C) pool. In this study, we investigated the effect patterns of antecedent moisture on bacterial 16S rRNA composition, microbial respiration and the soil extractable organic carbon (EOC) pool by examining soils subjected to rewetting, drying and maintenance at constant moisture conditions. Bacterial community composition depended on both antecedent and current soil moisture. Specifically, rewetting decreased the relative abundance of Actinobacteriota and increased that of Proteobacteria, Myxococcota, Acidobacteriota and Gemmatimonadota, while that of Actinobacteriota, Proteobacteria, Chloroflexi and Entotheonellaeota increased after drying. The drying and rewetting treatments significantly affected substrate availability, as rewetting from antecedent drought facilitated the enrichment of soil EOC and induced a pulse in the respiration rate compared to drying from antecedent wetting. Additionally, most of the rewetting treatments increased the relative abundances of aromatic compounds. Soil moisture contents finally at 80 % water holding capacity (WHC) were most suitable for microbial respiration. Except for extreme drying, drying and rewetting treatments reduced C loss as drying promoted the integration of organic matter into the EOC pool via the desorption of aromatic substances and/or the lysis of microbial cells, which stimulated microbial respiration. The mechanistic and quantitative insights into the effects of antecedent moisture conditions on the soil C dynamic provided by this study will help reduce uncertainty in predicting soil C using current models.