Response of vegetation community structure, soil carbon sequestration, and water-holding capacity in returning farmland to grassland plots, in the agro-pastoral transitional zone in the Three Rivers Source Region

The present study aimed to explore the response of vegetation community succession, soil carbon sequestration, and water conservation capacity in returning farmland to grassland plots in the agro-pastoral transitional zone in the source region of the Three Rivers. The study region was a returning farmland to grassland demonstration zone in Guomaying town, Qinghai province and the study analyzed the changes in plant community succession, soil carbon sequestration, and water-holding capacity by field monitoring and laboratory experiments. The results demonstrated that: 1) After 11 years, total coverage, average height, number of layers of plants, and aboveground biomass in returning farmland to grassland plots all reached the same levels as the original vegetation, and the Shannon-Wiener diversity index and Pielou evenness index reached 80.9% and 97.5%, respectively, of the original vegetation. 2) After 11 years, the soil bulk density of the 0-40 cm layer of returning farmland to grassland plots decreased by 5% compared to the original vegetation plots, and the saturation moisture capacity, capillary moisture capacity, and field capacity of returning farmland to grassland plots were 12.6, 9.4, and 11.2 mm greater than that of the original vegetation plots, respectively. 3) After 11 years in the returning farmland to grassland plots, the soil organic carbon density and C/N had significantly increased by 31.85% and 37.63%, respectively, compared to the original vegetation plots (P<0.05), and there was no significant difference between the soil total nitrogen density of the returning farmland to grassland plots and the original vegetation plots (P>0.05). The results indicate that the returning farmland to grassland plots have benefited from restoration of the ecological environment in desert pastures in the agro-pastoral transitional zone. This is an effective measure to contain and improve the desertification in the source region of the Three Rivers.