Alpine meadow degradation enhances the temperature sensitivity of soil carbon decomposition on the Qinghai–Tibetan plateau

Grassland degradation is widespread globally, yet limited information is available on the effects and mechanisms of grassland degradation regarding the response of soil organic carbon (SOC) to temperature change. This is especially true for alpine regions, which can have high SOC storage and are extreme vulnerability to global warming. Here, we studied the temperature sensitivity of SOC decomposition (Q10, proportional change in decomposition rate for a 10 °C difference in temperature) in both the topsoil (0–10 cm depth) and subsoil (20–30 cm) along an alpine meadow degradation gradient on the Qinghai–Tibetan plateau (QTP). Q10 values were increased in response to alpine meadow degradation (severely degraded (2.42) > moderately degraded (2.20) > non-degraded (2.11)) and were higher in subsoil (2.34) than in topsoil (2.14) as a whole. Soil carbon quantity and quality and extracellular enzyme activities all decreased significantly with increasing degradation levels and soil depths. Among all the factors considered (soil texture; soil pH; carbon quantity, availability, and quality; and enzyme activities), Q10 values were found to be primarily mediated by carbon quality and enzyme activities. This result supported the “carbon-quality temperature” hypothesis in degraded alpine grassland, and that considering soil carbon quality and enzyme activity could improve predictions of the feedbacks between soil carbon and global warming under grassland degradation. Our findings suggest that alpine meadow degradation will further increase the losses of SOC in a warming climate, making the ecosystem more vulnerable to climate change.