Linking soil organic carbon dynamics to microbial community and enzyme activities in degraded soil remediation by reductive soil disinfestation

Reductive soil disinfestation (RSD) is a widely practiced strategy for remediating soil degradation that seriously threatens crop production and sustainable agriculture. However, the soil organic carbon (SOC) dynamics and its underlying mechanisms induced by RSD remain unknown. To clarify this problem, a field experiment explored the SOC dynamics under degraded soils (C3) remediated with CK (untreated) and RSD (combination of added maize straw (C4), water flooding, and plastic mulch). The relationships of SOC dynamics with microbial community composition and activities of C-related hydrolase were also disentangled using structural equation model (SEM) and variation partitioning analysis (VPA). Results indicated that the SOC concentration under CK treatment decreased by 0.96 g C kg−1 compared with that in the initial soil, while the SOC concentration under RSD treatment increased by 1.26 g C kg−1 because of old SOC loss (0.56 g C kg−1) and new SOC formation (1.82 g C kg−1). Compared to the CK, the RSD increased the soil dissolved organic C (DOC), but decreased the microbial biomass C (MBC) and abundances of bacteria and fungi. The soil microbial community shifted from Proteobacteria and Actinobacteria to Firmicutes and Ascomycota after RSD treatment, and the activities of C-related hydrolase were also enhanced, such as β-glucosidase, cellobiohydrolase, β-xylosidase, and invertase. The SEM and VPA suggested that the new SOC formation and the reduced old SOC loss under RSD treatment were collaboratively driven by soil properties (i.e., redox potential, DOC, and MBC), microbial taxa (i.e., Arthobacter, Symbiobacterium) and hydrolase activities (i.e., BG and CBH). Meanwhile, the RSD doubled the yield of subsequent tomato by mitigating soil degradation (i.e., salinization and Fusarium oxysporum) and increasing the SOC concentration. In summary, RSD, as a remediation strategy for soil degradation, can increase SOC concentration by modifying microbial community and C-related hydrolase activities.