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

Abstract

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 SOM decomposition (RS) and temperature sensitivity (Q10) determined in a short-term laboratory incubation with gradual warming from 5 to 29°C of soils from different elevations in the Qilian Mountains, China (2600, 2800, 3000, and 3200 m). The results showed the RS significantly increased with increasing elevation (p < 0.001), in which RS was significantly greater at 3200 m than that at the other elevations but had no significant difference in RS among elevations below 3200 m. Across all elevations, RS first showed an increasing trend at temperatures <20°C and then declined substantially (>20°C), 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 decreasing incubation temperature (p < 0.001). Meanwhile, soil organic carbon (SOC), total nitrogen, and 1- to 2-mm aggregate-associated organic carbon (OC) were the main control factors affecting RS and Q10 along an elevational gradient. These results indicate that high-altitude soils in alpine forests of the Qilian Mountains are relatively more sensitive to warming and have greater potential to release CO2 due to higher SOC contents and 1- to 2-mm aggregate-associated OC than low-altitude soils. The findings could serve as a reference for how regional C pools may respond to future warming in alpine forests of the Qilian Mountains.