A study on the recovery effect of extremely degraded grassland vegetation and soil carbon and nitrogen under mixed- and single-sown measures

To clarify the effects of revegetation on the vegetation, soil physical properties, and soil carbon and nitrogen contents of extremely degraded grasslands (EDG), we studied the vegetation characteristics, soil physical properties, and soil carbon and nitrogen contents of four-year-old single-sown grassland (SSG) and mixed-sown grassland (MSG) established on EDG and non-degraded grassland (NDG) (as a control). The results showed that the aboveground biomass values of the vegetation reconstructed grasslands were significantly higher than those of the EDG and NDG (P < 0.05). The total organic carbon content was 32.13 g·kg⁻¹ in the NDG and only 16.44 g·kg⁻¹ in the EDG, It was 18.65 g·kg⁻¹ and 17.21 g·kg⁻¹ in the MSG and SSG, respectively; these values were 58.05% and 53.56% higher than those for the NDG. The total nitrogen and soil microbial carbon nitrogen contents of MSG and SSG were significantly lower than those of NDG (P < 0.05) and not significantly different from those of EDG. Correlation analyses of each grassland vegetation and soil index showed that after vegetation reconstruction, a series of changes occurred in the vegetation biomass and soil status, and vegetation and soil indicators influenced each other. The combined analysis, using entropy-weighted-TOPSIS method, for each grassland showed that the C_i values of the four-year-old MSG and SSG were higher than those of EDG, and the C_i values of mixed-sown grassland were higher than those of single-sown grassland. In conclusion, the vegetation biomass and soil carbon and nitrogen stocks of EDG increased after vegetation reconstruction, and the MSG had a better recovery effect than the single-sown grassland.