Variations in soil δ13C with alpine meadow degradation on the eastern Qinghai–Tibet Plateau

Abstract

The alpine swampy meadow is a unique meadow type on the eastern Tibetan Plateau and is undergoing degradation. However, little is known about the responses of soil δ13C to alpine meadow degradation. Monitoring the β value, which is the slope of the linear regression relating soil δ13C to the logarithm of soil organic carbon (SOC) content, provides an approach to infer SOC dynamics. In this study, we investigated soil δ13C and SOC contents along a soil profile (0–50 cm), together with several soil physicochemical and biomass properties in a swampy meadow (SM), a grassland meadow (GM), and a degraded meadow (DM). Then, the variations in soil δ13C and β values and the main factors affecting them were analyzed. The results showed that soil δ13C increased with soil depth, but SOC decreased. The soil δ13C in the surface layer (0–10 cm) was comparable between GM and DM but was significantly lower in SM, and soil moisture was the major factor influencing the surface soil δ13 value. The three meadow types could be ranked, from highest β value to lowest, as follows: GM > SM > DM. The soil C/N ratio and soil texture explained large proportions of the variations in β value. Our results demonstrated that the degradation of alpine meadows affects biomass and soil physicochemical properties, leading to a reduction in C inputs and an accelerated rate of SOC decomposition, followed by a decrease in SOC content. Our findings also indicated that monitoring changes in soil δ13C is an effective method to evaluate the degradation of alpine meadows, but it should be used with caution. This study provides a more comprehensive understanding of soil δ13C and SOC dynamics with alpine meadow degradation.