Time coordination between cellulose-degrading complex microflora and enzymes on improving soil organic carbon turnover and stabilization in the saline-alkali soils

Straw incorporation is widely recommended as an agronomic practice for enhancing soil organic carbon (SOC). However, the severe environmental characteristic of saline-alkali soils suppresses microbial activity and extracellular enzyme production, thereby constraining the transformation and stabilization of straw-derived carbon into SOC. The application of straw-degrading microorganisms or hydrolytic enzymes can substantially accelerate straw decomposition. In this study, a microcosm experiment was conducted to investigate the synergistic effects of cellulose-degrading complex microflora and enzymes on the transformation and stabilization of straw-derived carbon into SOC in saline-alkali soils. The results showed that enzymatic treatment significantly increased the degradation rates of cellulose and hemicellulose at 30 days but had no significant effect on lignin degradation. The activities of cellulase, xylanase, and BETA-glucosidase at 60 days were significantly lower than those observed at 30 days. In contrast, the complex microflora significantly promoted the degradation of cellulose, hemicellulose, and lignin, enhanced overall straw decomposition, and substantially increased SOC content at 60 days in saline-alkali soils. These results suggested that complex enzymes primarily function during the early stages of straw decomposition, whereas complex microflora exert their effects predominantly during the later stages. During the early stage, the synergistic application of cellulose-degrading complex microflora and enzymes, primarily driven by enzymatic activity, increased the relative abundance of Ascomycota and genes associated with labile carbon degradation, thereby enhancing the efficiency of straw-derived carbon conversion into SOC. In the later stages, the synergistic effects were predominantly driven by the complex microflora, which increased the relative abundance of Basidiomycota and genes associated with recalcitrant carbon degradation, thereby promoting the conversion of particulate organic carbon (POC) to mineral-associated organic carbon (MAOC). Overall, this study demonstrates a temporally coordinated effect of cellulose-degrading complex microflora and enzymes on the regulation of SOC turnover and stabilization in saline-alkali soils.