Soil organic carbon and its stability after vegetation restoration in Zoige grassland, eastern Qinghai-Tibet Plateau

Soil organic carbon (SOC) shapes carbon cycling and climate. Grassland degradation has greatly reduced the SOC of these biomes. However, vegetation restoration is effective at improving the SOC of degraded grasslands, the sustainability of the outcomes of which is unclear. Therefore, we studied the effects of vegetation restoration on SOC and its stability in perspective of three restoration practices (i.e. Hippophae rhamnoides Linn., Elymus nutans Griseb., Avena nuda, and their combinations) in Zoige, a climatically sensitive area located at the eastern Qinghai-Tibet Plateau. Topsoil samples (0-10 cm) were collected within each restoration practice to analyze SOC and its fraction contents, soil aggregates, and aggregate-associated SOC content. Results showed that SOC in the control (CK) was 2.77 g kg(-1), and vegetation restoration increased the SOC contents by 10.12, 73.00, and 15.81%, respectively. Vegetation restoration significantly increased the easily oxidizable carbon (EOC) and decreased recalcitrant organic carbon (ROC), highlighting different responses of SOC fractions to vegetation restoration. Soil macroaggregate was 8.74% in CK, which was significantly lower than that after vegetation restoration (57.08-81.01%). Vegetation restoration had no impact on non-aggregated silt + clay fraction-associated SOC and significantly increased macroaggregate-associated SOC content, which was the major contributor of total SOC. These findings suggest that vegetation restoration may affect SOC stability by increasing SOC and EOC, decreasing ROC, and changing the compositions of aggregates and aggregate-associated SOC. However, our study was conducted 3 years after vegetation restoration, which maybe too short of a period to accurately determine SOC stability.