Soil organic carbon decomposition in response to moisture, microbial communities, and biochar addition in Alfisols

Abstract Soil organic carbon (SOC) decomposition is influenced by fluctuations in moisture levels, which play a crucial role in regulating global soil carbon balance. Biochar is widely used as an amendment to enhance carbon sequestration and soil health. However, the effects of biochar addition and moisture variability on SOC decomposition remain debated. Therefore, we conducted a microcosm incubation experiment to examine how moisture variability intensity and biochar addition affect SOC decomposition in an Alfisol topsoil from Northeast China. Our results show that increased soil moisture variability accelerates SOC decomposition by 0.5–17.2%, enhances total phospholipid fatty acid (PLFA) content by 29.9–39.6%, and raises the Gram-positive to Gram-negative (GP: GN) bacterial ratio by 2.1–11.0%. Additionally, moisture variability intensifies soil residual clay fraction particle content by 0.4–27.5%, contributing further to SOC decomposition. Biochar addition mitigates the impact of moisture fluctuations on SOC decomposition by stabilizing soil aggregates. These findings highlight the key roles of soil microbial communities and aggregate structure in governing SOC decomposition. Graphical Abstract