Depth dependence of soil carbon temperature sensitivity across Tibetan permafrost regions

Permafrost regions with high soil organic carbon (SOC) storage are extremely vulnerable to global warming. However, our understanding of the temperature sensitivity of SOC decomposition in permafrost regions remains limited, leading to considerable uncertainties in predicting carbon-climate feedback magnitude and direction in these regions. Here, we investigate general patterns and underlying mechanisms of SOC decomposition rate and its temperature sensitivity (Q(10)) at different soil depths across Tibetan permafrost regions. Soils were collected at two depths (0-10 and 20-30 cm) from 91 sites across Tibetan permafrost regions. SOC decomposition rate and Q(10) value were estimated using a continuous-flow incubation system. We found that the SOC decomposition rate in the upper layer (0-10 cm) was significantly greater than that in the lower layer (20-30 cm). The SOC content governed spatial variations in decomposition rates in both soil layers. However, the Q(10) value in the upper layer was significantly lower than that in the lower layer. Soil pH and SOC decomposability had the greatest predictive power for spatial variations in Q(10) value within the upper and lower layers, respectively. Owing to the greater temperature sensitivity in the lower layer, our results imply that subsurface soil carbon is at high risk of loss, and that soil carbon sequestration potential might decrease in these regions in a warming world.