Abstract: Organic carbon in permafrost regions has a rapid and strong response to climate warming. In this study, we analyzed the distribution of soil organic carbon (SOC) and its influencing factors, with 120 soil samples from 40 sampling points in the permafrost source region of the Yangtze River, China. The results showed that SOC contents at 0-10 , 10-20, and 20-30 cm soil depths were 8.00±4.95, 7.65±5.21, and 7.28±5.00 g·kg^-1, respectively. Average SOC contents within 0-30 cm at 4400-4500, 4500-4600, 4600-4700, 4700-4800, 4800-4900, 4900-5000, 5000-5100, 5100-5250 m altitudes were 3.25±0.43, 3.67±1.88, 7.76±4.77, 7.62±3.24, 6.78±3.28, 7.85±4.94, 11.61±4.31, 11.48±4.73 g·kg^-1, respectively. Average SOC contents within 0-30 cm at 33°-34°, 34°-35°, and 35°-36°N latitudes were 9.47±4.44, 3.42±2.04, and 4.21±1.58 g·kg^-1, respectively. SOC content decreased with increasing soil depth and increasing latitude, but increased with increasing altitude. SOC content was positively correlated with the mean annual normalized difference vegetation index, mean annual precipitation, volumetric water content, total nitrogen, and cation exchange capacity (P<0.01), and was negatively correlated with mean annual temperature and pH at all three depths (P<0.01). Soil bulk density had a significant effect on SOC content at 0-10 cm depth (P<0.05). Clay content significantly affected SOC content at the 0-10 and 10-20 cm depths (P<0.05). Mean annual temperature and mean annual precipitation were the main factors affecting the distribution of SOC in the study area. These results provide basic data and theoretical support for accurately simulating and estimating SOC storage in the permafrost regions in the source region of the Yangtze River.

Key words: Qinghai-Tibet Plateau, source region of the Yangtze River, permafrost, organic carbon, influencing factor.