Vegetation Restoration Affects SOC Stability in Topsoil and Subsoil in Zoige Grassland, Eastern Qinghai‐Tibet Plateau

Abstract

Vegetation restoration has been evidenced as a crucial practice to improve soil organic carbon (SOC) content in grassland. However, the impacts of vegetation restoration on SOC chemical stability and its regulation mechanisms are not fully understood, particularly on the Qinghai‐Tibet Plateau. To address this knowledge gap, we assessed the effects of vegetation restoration after 6 years on SOC chemical stability at the 0–10, 10–30, and 30–50 cm layers in the Zoige alpine grassland, using 13 C nuclear magnetic resonance (NMR) spectroscopy. The results showed that vegetation restoration increased SOC contents across soil layers. However, vegetation restoration induced different responses of SOC chemical stability across soil depths. In the 0–10 cm layer, vegetation restoration decreased SOC chemical stability by increasing abundances of lignin and cellulose degradation genes by 19%–40%, which accelerated the decomposition of Aromatic carbon (C) and reduced the Aromatic C/O‐Alkyl C ratio. Conversely, vegetation restoration increased SOC chemical stability at the 10–30 and 30–50 cm layers due to the increased abundance of C‐fixation genes. Such increase elevated the accumulation of Alkyl C and Aromatic C but reduced O‐Alkyl C contents, leading to an increase of the Alkyl C/O‐Alkyl C and Aromatic C/O‐Alkyl C ratios by 56% and 48%. These results confirmed that vegetation restoration shapes vertical patterns in SOC chemical stability by increasing the functional potential of C‐degradation genes in the 0–10 cm layer and enhancing C‐fixation genes in the 10–50 cm layer. These findings highlight the vertical heterogeneity of SOC chemical stability following vegetation restoration and emphasize that layer‐specific dynamics should be considered when predicting long‐term SOC sequestration.