The effect of climatic and edaphic factors on soil organic carbon turnover in hummocks based on δC on the Qinghai-Tibet Plateau.

Hummocks (thúfur, pounus) are peculiar landforms usually formed by repeated freeze-thaw processes and differential frost heave, and are common in frost soil regions, especially in the Qinghai-Tibet Plateau. However, little is known about the response of δC in soil organic carbon (δC) to soil and climate properties in hummocks. The β value indicates the decomposition rate of soil organic carbon (SOC) in soil, and was obtained from the slope of the regression between the log10-transformed SOC concentration and δC in soil depth profiles. In this study, we investigated δC and SOC contents along a soil profile (0-60 cm), together with edaphic and climatic properties, both in hummocks and control plots (alpine grasslands) on the northeastern Qinghai-Tibet Plateau. Then, the variations in δC and β values, and the main factors affecting them, were analyzed. The results show that δC increases with soil depth, while SOC decreases both in the hummocks and control plots. However, β values in the hummocks were significantly (P < 0.05) higher than in the control plots while δC showed no difference between hummock and control. Redundancy analysis showed that altitude is the main control factor for δC and β in the hummocks. Climate type was the main factor affecting δC in the control plots, while mean annual precipitation and soil fractal dimension were the main factors controlling β. Overall, climate, rather than soil, is the key factor that affects the carbon turnover rate in the hummock in the northeastern QTP. The findings of this study will expand our understanding of the soil carbon cycle and δC changes, especially in the case of hummocks.