Abstract: The importance of grasslands to soil carbon sequestration and global carbon cycle has been well recognized. About 95% of the carbon in grasslands of China is stored in soil. We selected four desertified grasslands with different restoration durations of 0, 1, 4, 8 years to examine the changes of soil carbon pool and root characteristics during the restoration of alpine grassland in Zoige. The results showed that soil carbon content in Zoige alpine grassland was affected by restoration duration and soil depth. The contents of soil total carbon, organic carbon, and inorganic carbon in the restored grasslands were higher than those in the unrestored grassland. Soil organic carbon content was the highest in the grassland restored for 8 years, while inorganic carbon content was the highest in the grassland restored for 1 year, which were 7.55 and 11.78 times of that in the unrestored grassland, respectively. Soil organic carbon content in surface layer (0-20 cm) was lower than that in deep layer (20-50 cm) in the grassland restored for 1 year and 4 years, while soil organic carbon content in surface layer was higher than that in deep layer in the grassland restored for 8 years. Soil inorganic carbon content in the grassland restored for 1 year, 4 years, and 8 years was the highest in 0-5 cm soil layer. The ratio of soil organic carbon to inorganic carbon was in an order of the grasslands restored for 4 years > 8 years > 1 year, and the proportion of soil organic carbon in deep layer (20-70 cm) was higher than that of surface layer (0-20 cm). Root characteristics (root length, root volume, tissue density, and root biomass) increased with increasing restoration time, and were significantly positively correlated with soil organic carbon, but not with soil inorganic carbon content. Soil inorganic carbon content was positively correlated with pH. During the restoration of desertified grassland, soil carbon content significantly increased, and plant community and soil physicochemical properties were gradually improved. Therefore, secondary succession on degraded grassland under artificial intervention is an effective strategy to increase soil carbon sink in degraded alpine grasslands.

Key words: Zoige, desertified grassland, soil total carbon, root characteristics, grassland restoration.