Land use conversion impacts on the stability of soil organic carbon in Qinghai Lake using 13C NMR and C cycle‐related enzyme activities

Abstract Soil organic carbon (SOC) plays a major role in maintaining long‐term ecological stability. This paper focuses on how land use conversion affects the stability of SOC (e.g., carbon [C] molecular structure) and how soil C cycle‐related enzyme activities are involved in the process. Four land use types around the southern margin of Qinghai Lake were researched: lakeside wetland, natural grassland, cropland, and restored grassland. Soil C was dominated by O‐alkyl carbon (O‐alkyl C, 40.6%–49.3% of total intensity) and alkyl carbon (alkyl C 25.9%–36.7%) in all land use types. Alkyl C and aliphaticity were more abundant in lakeside wetlands than in the other land use types; these values decreased by 29.5% and 36.0%, respectively, after lakeside wetland reclamation. Compared with cropland, restored grassland had higher dissolved organic carbon and β‐glucosidase activity, mainly attributed to the higher plant residues left in the topsoil that provided the polysaccharides required for the higher β‐glucosidase activity. The SOC, labile carbon, alkyl C, and aliphaticity together explained more than 50% of the total variability of soil enzyme activities ( p < 0.05) by redundancy analysis, and β‐glucosidase played a regulatory role in soil carbon conversion by path analysis. The lakeside wetland had a more stable SOC than the other land use types around Qinghai Lake at the molecular level due to its higher aliphaticity and aromaticity, which are mainly related to oxygen limitations in lakeside wetlands. To some extent, the accumulation of recalcitrant molecules is limited in restored grassland soils.