Objective The aims was to investigate the differences in soil organic carbon (SOC) content in microtopography in the Qilian Mountains, in order to provide a scientific basis for the assessment of carbon sequestration effect of the complex terrain.

Method Based on the combination of field measurements and indoor analysis, this study analyzed the SOC content of Qinghai spruce woodland and alpine grassland at the slope scale and analyzed the influencing factors.

Result ① SOC contents gradually decreased with the deepening of soil depth, and there was a significant difference of SOC content between the shady and sunny slopes (P < 0.05). The trend of SOC content in Qinghai spruce woodland was mid-slope (PZ) > upper mid-slope (PZS) > upper bottom of slope (PDS) > bottom of slope (PD) > top of slope (PS) > top of slope (PSD), and that of alpine grassland was mid-slope (PZ) > bottom of slope (PD) > upper middle of slope (PZS) > upper bottom of slope (PDS) > top of slope (PS) > top of slope (PSD). ② The SOC content was greatest from 3060 ~ 3090 m for both shady and sunny slopes at different elevation intervals. ③ The comprehensive analysis of geo-detector showed that the distribution of SOC was not dominated by a single factor, but that was influenced by multiple environmental factors with a significant characteristic of multiple drivers. Under the control of a single factor on sunny slopes, bulk density had the highest explanation rate of 19%; under the interaction of factors, bulk density coupled with elevation was the dominant factor affecting SOC, with an explanation rate of 37%. Under the control of a single factor on the shaded slope, the highest explanation rate of soil SOC content was 35% for bulk density. While under the factor interaction, the coupling of elevation and silt content was the dominant factor for SOC content on the shaded slope, with an explanation rate of 54%.

Conclusion Comparing the SOC contents of two vegetation types, the SOC content of Qinghai spruce woodland was higher overall. The results of SOC distribution on different slopes showed that Qinghai spruce woodland was particularly rich in SOC in the middle (PZ) and upper middle (PZS) regions of the slope. On the contrary, the maximum SOC content of alpine grassland appeared at the bottom of the slope (PD).