Dynamics of soil organic carbon under wheat cultivation in saline soil of the Yellow River Delta.

The stability of soil organic carbon (SOC) in the saline-alkali farmlands of the Yellow River Delta is influenced by both salt stress and planting patterns. Understanding how these factors jointly regulate soil carbon pools and their active components is crucial for analyzing carbon cycling in saline-alkali lands and optimizing soil improvement strategies. This study focuses on coastal saline-alkali farmlands in the Yellow River Delta, comparing a control plot of untreated bare land with a treatment plot where wheat is cultivated following rice. Utilizing the natural salt gradient, we systematically analyzed the variations in soil water-salt environment, nutrients, enzyme activities, SOC and its active components, during the jointing, flowering, and maturity stages. Through correlation analysis, random forest, redundancy analysis, and partial least squares path modeling, we quantified how soil environmental factors regulate organic carbon components.The findings indicate that wheat cultivation significantly alters the soil water-salt and nutrient patterns in saline-alkali lands, generally enhancing soil enzyme activities. The impact of wheat cultivation on the carbon pool is modulated by salt intensity. In low-salt environments, the toxic effects of salt ions on microorganisms are mitigated, promoting the accumulation of active organic carbon components. Conversely, moderate to high salt stress significantly inhibits soil carbon turnover, with total organic carbon in the surface layer declining under these conditions. Regarding driving mechanisms, sucrase activity emerged as the key environmental factor influencing SOC changes in wheat cultivation systems. In contrast, cellulase activity and available phosphorus content were more influential in explaining organic carbon variation in the bare land system, highlighting distinct driving mechanisms of carbon pools between the two systems.Compared to the control, wheat cultivation notably enhanced the explanatory power of soil environmental factors for variations in active organic carbon components, reconstructing the regulatory network of the soil carbon cycle in saline-alkali farmlands. This study elucidates the differential and stage-specific regulatory mechanisms of wheat cultivation and salt gradients on the organic carbon pool in coastal saline-alkali lands, offering a theoretical foundation for the improvement and fertilization of saline-alkali lands and the maintenance of soil carbon pools in the Yellow River Delta.