Climate and Soil Geochemistry Influence the Soil Organic Carbon Content in Drylands of the Songliao Plain, Northeast China

The understanding of the spatial distribution of soil organic carbon (SOC) and its influencing factors is crucial for comprehending the global carbon cycle. However, the impact of soil geochemical and climatic conditions on SOC remains limited, particularly in dryland farming areas. In this study, we aimed to enhance the understanding of the factors influencing the distribution of SOC in the drylands of the Songliao Plain, Northeast China. A dataset comprising 35,188 measured soil samples was used to map the SOC distribution in the region. Multiple linear regression (MLR) and random forest models (RFM) were employed to assess the importance of driving indicators for SOC. We also carried out partial correlation and path analyses to further investigate the relationship between climate and geochemistry. The SOC content in dryland soils of the Songliao Plain ranged from 0.05% to 11.63%, with a mean value of 1.47% ± 0.90%. There was a notable increasing trend in SOC content from the southwest to the northeast regions. The results of MLR and RFM revealed that temperature was the most critical factor, demonstrating a significant negative correlation with SOC content. Additionally, iron oxide was the most important soil geochemical indicator affecting SOC variability. Our research further suggested that climate may exert an indirect influence on SOC concentrations through its effect on geochemical properties of soil. These insights highlight the importance of considering both the direct and indirect impact of climate in predicting the SOC under future climate change.