Grazing exclusion did not affect soil properties in alpine meadows in the Tibetan permafrost region

摘要

Grazing exclusion (GE) is widely used in the Tibetan Plateau of China to restore degraded grasslands. However, the effects of GE on vegetation and soil properties in alpine meadows are still not well understood. We compared GE with adjacent continuously grazing alpine meadows at five sites to evaluate the impact of GE (10-14 years) on vegetation and soil properties in the permafrost region of the Tibetan Plateau. We collected soil samples at two soil depths (0-20 and 20-40 cm) from GE and adjacent grazing sites. The results showed that GE and Site had significant effects on aboveground biomass and cover, Site but not GE had significant effects on diversity index. GE significantly increased the aboveground biomass and cover in three of the five sites, particularly where vegetation cover was greatest. At each site, GE had inconsistent effects on plant species diversity (a positive effect at one site, no significant effects at three sites, and a negative effect at the other site). No significant differences were found between GE and adjacent grazing grasslands in soil properties (soil organic carbon [SOC], total nitrogen [N], total phosphorus [P], available P, mineral N, microbial biomass carbon [MBC] and nitrogen [MBN] and pH) for both soil depths at each site. A general linear mixed model confirmed that site and sampling depth, rather than GE, significantly affected soil properties (except for MBC). Both total aboveground biomass and cover were positively correlated with soil total P, MBC and MBN, were negatively correlated with available P and pH, and were not significantly correlated with SOC and total N. The results indicate that long-term GE (10-14 years) in alpine meadow did not significantly impact soil properties, and its impact on plant biomass and vegetation cover depends on the vegetation condition of the site. Our results can provide new insights for alpine meadow management in the permafrost region of the Tibetan Plateau.