中国表层土壤有机碳密度估算与时空演变分析

Estimation of Topsoil Organic Carbon Density and Its Spatial-temporal Changing in China

摘要:

土壤有机碳（Soil organic carbon, SOC）在全球碳循环中起着至关重要的作用，随着全球气候变化和人类活动的影响，土壤有机碳密度（Soil organic carbon density, SOCD）不断发生变化。本研究提出了一种基于气候区划与随机森林模型的SOCD估算方法，开发了我国1980s—2020s长时间序列、空间分辨率为1 km的SOCD产品，并分析了我国1980s—2020s SOCD的空间异质性及演变规律。利用Landsat系列卫星影像、高程数据、气象数据和实测SOCD数据，构建基于随机森林模型的数字土壤制图方法，估算中国0～20 cm表层SOCD时空分布。研究结果表明，考虑气候分区的模型预测精度（R2=0.55，RMSE为2.19 kg/m2）优于全局模型（R2=0.46，RMSE为2.36 kg/m2）。气象因素对SOCD的影响显著，气温升高会加速微生物代谢速率，促进土壤有机物质分解，导致SOC释放增加;降水对土壤水分状况有直接影响，适宜的土壤含水率有利于SOC积累。通过与黑河流域的实测数据进行验证，模型估算结果与实测数据达到了较高一致性（R2=0.69，RMSE为2.01 kg/m2）。研究结果为中国SOCD的精确估算与分析提供了科学依据，对于优化农业实践，提升土壤碳汇功能，实现国家“双碳”目标具有重要指导意义，有助于推动可持续农业发展和生态环境保护。

Abstract:

Soil organic carbon (SOC) plays a crucial role in the global carbon cycle, and with the influence of global climate change and human activities, soil organic carbon density is constantly changing. A soil organic carbon density (SOCD) estimation method was proposed based on climate regionalization and a random forest model. It also developed a SOCD product with a long time series from the 1980s to 2020s and a spatial resolution of 1 km. The spatial heterogeneity and evolution patterns of SOCD in China from the 1980s to the 2020s were analyzed. Using Landsat series satellite images, elevation data, meteorological data, and measured SOCD data, a digital soil mapping method based on the random forest model was constructed to estimate the spatio-temporal distribution of 0~20 cm surface SOCD in China. The results showed that the prediction accuracy of the model considering climate zoning (R2=0.55, RMSE was 2.19 kg/m2) was better than that of the global model (R2=0.46, RMSE was 2.36 kg/m2). Meteorological factors had a significant impact on SOCD. Increasing temperature would accelerate the metabolic rate of microorganisms, promote the decomposition of soil organic matter, and lead to the increase of soil organic carbon release. Precipitation had a direct effect on soil water status, and suitable soil water content was conducive to SOC accumulation. At the same time, through verification with the measured data of the Heihe River basin, a high consistency was achieved between the model estimation results and the measured data (R2=0.69, RMSE was 2.01 kg/m2). The research result can provide a scientific basis for the accurate estimation and analysis of SOCD in China and it had important guiding significance for optimizing agricultural practice, improving soil carbon sink function, and realizing the national “double carbon” goal, which was conducive to promoting sustainable agricultural development and ecological environmental protection.