# Dynamic Changes in and Driving Factors of Soil Organic Carbon in China from 2001 to 2020
###### Abstract  
It remains unclear what changes have occurred in the distribution pattern of and trend in soil organic carbon (SOC) in China against the background of climate and land use change. Clarifying the dynamic changes in SOC and their driving factors in different regions of China is therefore crucial for assessing the global carbon cycle. In this study, we collected and supplemented a large amount of soil organic carbon density (SOCD) data in China from 2001 to 2020 and extracted data on environmental covariates (ECs) for the corresponding years. A random forest model was used to estimate the SOCD at a depth of 0-20 cm and 0-100 cm in China for the years 2001, 2005, 2010, 2015, and 2020, and we explored the trend of SOCD changes and their key driving factors. The results showed the following: (1) Compared with previous studies, the predictive ability of the 0-100 cm depth model was greatly improved; the coefficient of determination (R\({}^{2}\)) was 0.61 and [PERSON]'s concordance correlation coefficient (LCCC) was =0.76. (2) From 2001 to 2020, China's soil organic carbon stocks (SOCS) were 38.11, 39.11, 39.88, 40.16, and 41.12 Pg C for the 0-20 cm depth and 110.49, 112.67, 112.80, 113.06, and 114.96 Pg C for the 0-100 cm depth, respectively. (3) The effects of temperature and precipitation on SOCD in China showed obvious regional variability, and land use changes had mainly positive effects on SOCD in all regions of China, which was related to the large-scale implementation of ecological protection and restoration and the policy of returning farmland to forests and grasslands in China. This study provides strong scientific support for addressing climate change and rationalizing the use of land resources. change on the spatial and temporal scales is therefore an important issue in combating global warming. The current understanding of soil carbon feedbacks to climate change is inconsistent [12; 13]. On the one hand, studies have shown that temperature increases elevate microbial activity and promote the release of soil carbon from decomposition [14; 15]. On the other hand, it has also been shown that global warming promotes vegetation growth and increases the input of biological carbon to the soil [16; 17], facilitating carbon sequestration in the soil. Regarding the feedback of soil carbon to land use disturbance, studies have mainly dealt with the effects of different land use types (e.g., farmland, woodland, and grassland) and the intensity of land use change (e.g., tillage, crop rotation) on SOC content and dynamics [4; 18]. In general, existing studies have mainly explored the feedback of soil carbon based on a single factor, which is insufficient when exploring the dynamic effects both of climate change and different land disturbance intensities on SOC in different regions, especially at the continental scale. As a country with a diverse climate and complex land use types, China has experienced significant changes in regional climate in the context of global warming [19; 20]. In recent decades, with the rapid economic and social development and the need for ecological restoration and protection, land, as a uniformly controlled resource, has undergone dramatic changes in its utilization types, leading to continuous alterations to soil carbon pools [21; 22; 23; 24]. As a result, there are significant spatial differences in the changes in SOC and their driving factors in China, but the current research in this area lacks depth. In summary, the objectives of this study were as follows: (1) to construct a spatial and temporal prediction model for SOCD at depths of 0-20 cm and 0-100 cm in China from 2001 to 2020 and to analyze the trend of SOC change in different regions of China; (2) to reveal the regional differences in the impacts of climate and land use change on SOC in China. The results of this study help to clarify the impacts of climate and land use change on the historical evolution of the SOC pool in China and are important for achieving carbon neutrality and assessing the global carbon cycle.