Elevational variability and controls on temperature sensitivity of soil organic matter decomposition in alpine forests of northwestern China

Patterns and elevational controls on the response of soil organic matter (SOM) decomposition to temperature in alpine forest soils are critical to efforts to quantify the regional carbon cycle-climate feedback, but are not well known. Here, we report rates of soil organic matter (SOM) decomposition (Rs) and temperature sensitivity (Q10) determined in a short-term laboratory incubation with a gradual warming from 5°C to 29°C of soils from different elevations in the Qilian Mountains, China (2,600, 2,800, 3,000, and 3,200 m). The results showed the Rs significantly increased with increasing elevation (P<0.001). Across all elevations, RS first showed an increasing trend at temperatures < 20 ℃ and then declined substantially, most likely in response to the content of labile C (greater at the start of incubation, and declining over time). Q10 of SOM decomposition increased significantly with increasing elevation and deceasing incubation temperature (P<0.001). More importantly, soil organic carbon (SOC), total nitrogen (TN), 1-2 mm aggregate-associated OC, and elevation were the main control factors affecting Rs and Q10. These results indicate that high-altitude soils in alpine forests of the Qilian Mountains are relatively more sensitive to temperature changes, and have greater potential to release CO2 due to higher SOC contents and 1-2 mm aggregates-associated OC than low-altitude. The findings could serve as a reference for how regional C pools may respond to future warming in alpine forests of the Qilian Mountains.