The changes of vegetation community characteristics led to the reconstruction of soil microbial communities and functions during the cultivation of degraded alpine meadows

Abstract

Unreasonable grassland use has degraded the alpine meadow on the Qinghai-Tibetan Plateau in the past half a century, and approximately 32.1% of the degraded meadows degenerated to bare grassland. Artificial grassland reconstruction is a widespread measure for rebuilding the grassland ecosystems of these bare grasslands. However, does the soil microbe community structure improve with the aboveground vegetation restoration? Which microflora are more sensitive to environmental changes are not unclear. Thus, we analyzed four artificial grasslands established for different years on extreme-degraded (ED) grasslands of the alpine meadows. These artificial grasslands were rationally utilized by grazing Tibetan sheep and Yak from December to April and were completely grazing-prohibited in other seasons. In 2017, four plots of approximately 2400 m² for each artificial restoration grassland (3, 6, 9, and 12 years) were selected as treatments with non-degraded (ND) and ED meadows as controls. The potential predictors and regulators for soil microbial community structures and functions in the alpine meadows were evaluated. The results showed that artificial restoration did not affect soil microbe community compositions but dramatically changed the community constructions. The bacterial community structure was more sensitive to artificial interference than fungal. Actinobacteria, Acidobacteria, and Mortierellomycota could be used as indicators of environmental changes. Compared with ED grassland, the soil microbial biomass carbon increased significantly by 29.5% and 33.7% in 6 and 9 years grasslands, respectively. The species richness and below-ground biomass of grassland vegetation play a decisive role in soil microbial community and functional structures, while the soil water content and organic carbon, and soil elemental balance play a regulating role. Moreover, the abundance of soil bacteria with ureolysis and nitrogen fixation functions decreased significantly in grassland degradation, and soil pH played a major regulatory role. In conclusion, the vegetation and soil of artificial grasslands were in good condition after 6 years of artificial restoration. However, all the indexes declined to different degrees after 12 years of establishment, and the grassland ecosystem faced the risk of secondary degradation. The mixed sowing of many plant species with developed root systems should be adopted when artificially restoring degenerated alpine grasslands. Simultaneously, soil organic material supplementation and the balanced application of nitrogen and phosphorus fertilizers are recommended.