Temporal and Spatial Variation Characteristics of Soil Organic Carbon in Hulunbuir and Its Influencing Factors

This study aimed to analyze the spatiotemporal distribution characteristics and driving factors of soil organic carbon (SOC) content in Hulunbuir, China, in order to provide the scientific basis for soil carbon storage management and ecosystem services.

The point-to-point sampling survey method was used to collect measured SOC data from 1980 (historical data) and 2022, involving four land use types: farmland, grassland, forest, and wetland. Using regression kriging method, combined with environmental variables such as temperature, precipitation, slope, altitude, and NDVI, the spatial prediction of SOC content and its changes was carried out.

(1) The SOC content in 1980 was significantly affected by these five factors (P<0.05), while the SOC data in 2022 was mainly affected by altitude, slope, precipitation, and NDVI, with no significant effect from temperature (P=0.07). The fitting accuracies of the models for the two periods of 1980 and 2022 were R²=0.60 and R²=0.63, respectively, indicating that the predictive model had a certain level of reliability. (2) According to spatial prediction data, the average SOC content in Hulunbuir was 40.29 g·kg^-1 in 1980, and decreased to 31.75 g·kg^-1 in 2022. The spatial variation trend of soil SOC content in the two periods was similar, with higher content in the central region and lower content in the western and eastern regions. (3) There were differences in the changes of SOC content under different land use patterns. Over the past 40 years, the SOC content of farmland, grassland, forest, and wetland soils has decreased by 4.59 g·kg^-1 (13.3%), 6.08 g·kg^-1(18.7%), 11.16 g·kg^-1(23.0%), and 7.20 g·kg^-1(24.4%), respectively.

The spatial distribution trend of SOC content in Hulunbuir area remained consistent between 1980 and 2022, and SOC content showed a decreasing trend under different land use patterns. The transformation of land use patterns was a key factor affecting the spatial distribution changes of SOC. In addition, there was uncertainty in the prediction of SOC changes by environmental variables, and future research needs to consider their dynamic characteristics. In the Hulunbuir region, the forest grassland transition zone and the forest farmland transition zone had carbon sink potential, while grasslands, central high-altitude forest areas, and farmland areas might be carbon source areas.