Vegetation carbon input moderates the effects of climate change on topsoil organic carbon in China

Climate change affects soil organic carbon (SOC) and contributes to the uncertainty of terrestrial carbon sinks in the global carbon budget. With changes in vegetation growth and the regulation of its carbon input, the feedback of topsoil SOC to climate change is likely to become more complex at broad geographical scales. China has experienced noticeable changes in climate and surface greening in recent decades, and these changes have effectively influenced the dynamics of topsoil SOC. However, the potential role of vegetation carbon inputs in regulating and buffering climate change impacts on SOC in the context of current ecological restoration is still poorly understood. Therefore, to solve these problems, on the basis of the long-term satellite remote sensing data from 2000 to 2019, multiple linear regression and pathway analyses to investigate the dominant role of different climate factors and vegetation net primary productivity (NPP) on topsoil SOC changes in China, and further reveal the potential role of vegetation carbon inputs in regulating and buffering the effects of climate change on topsoil SOC. The results show that the overall trend of increase in topsoil SOC in China from 2000 to 2019 is significant (P < 0.05), and most regions show a good development trend in the future, except for some areas in the Central South, East, and Northeast regions, where a risk of degradation exists. Relative to climate change, the dominant areas of NPP impact on topsoil SOC in China occupy a considerable proportion, especially in the North, Northwest, and Central South regions, with area proportions of 68.15%, 49.52%, and 47.99%, respectively. Importantly, the indirect positive impacts of climate change on changes in topsoil SOC in China through vegetation carbon input offset the direct negative impacts in most areas. That is, over the past 20 years, increases in temperature and precipitation have led to decreases in topsoil SOC in most of China, whereas the ultimate net effect has been to increase topsoil SOC by promoting vegetation carbon input, particularly in the Loess Plateau region. Our study demonstrates that considering only the effects of climate change on SOC, while ignoring possible changes in carbon transfer from plants to soils, largely reduces the reliability of assessments of SOC stocks and their changes. These results have important implications for enhanced prediction of future SOC changes and provide references for terrestrial carbon sinks management strategies in the context of response to climate change.

Keywords: Topsoil organic carbon, Climate change, vegetation carbon input, Pathway analysis, China.