Abstract: The degradation of alpine meadows in the Three-River Source Region has posed an enormous threat to regional ecological safety. Recovery of soil organic carbon pool is the key to restore degraded alpine meadows. In this study, a degraded alpine meadow (DAM), an artificial grassland established for 3 years (AG3) and an artificial grassland established for 7 years (AG7) in the Three-River Source Region were chosen to quantitatively evaluate the changes in fractions and biochemical stability of soil organic carbon after establishing artificial grasslands using acid hydrolysis approach, which divided soil organic carbon pool into labile carbon pool I, labile carbon pool II, and recalcitrant carbon pool. The results showed that the contents of soil organic carbon fractions decreased following the order: recalcitrant carbon pool > labile carbon pool I > labile carbon pool II at all study sites, suggesting that recalcitrant carbon pool was the main component of soil organic carbon pool. After establishing artificial grassland for 3 years, the contents of soil total organic carbon, labile carbon pool I, and recalcitrant carbon pool did not change, whereas the content of soil labile carbon pool II significantly decreased in the 0-30 cm soil layer (P<0.05). By contrast, establishing artificial grassland for 7 years generally increased the contents of soil total organic carbon and most fractions except for labile carbon pool II. The recalcitrant index of soil organic carbon varied in ranges of 43.7%-48.4%, 42.3%-48.9% and 42.3%-53.4% at DAM, AG3 and AG7, respectively. Although the recalcitrant index of soil organic carbon at AG7 was higher than that at the other two sites, the difference was only significant in the 10-20 cm soil layer (P<0.05). In conclusion, the findings indicate that long-term artificial vegetation restoration is an effective way to improve the content and biochemical stability of soil organic carbon in degraded alpine meadow of the Three-River Source Region, which would contribute to the recovery of carbon sink function of soil.

Key words: soil organic carbon fraction, biochemical stability, artificial grassland, ecological restoration