Grassland reconstruction is a major approach to alleviate the ‘black beach’ in Sanjiangyuan of the Qinghai-Tibetan Plateau. It is vital to understand how to manage the planting grassland after reconstruction. And which artificial grassland management pattern is more likely to restore the degraded grassland of ‘black beach?’ To provide the scientific basis for the restoration of ‘black beach’, we investigated the changes in vegetation characteristics, soil physicochemical properties and soil microbial community structure of planting grassland under different management patterns, and explored the effect of the management patterns on community succession of planting grassland. In this study, vegetation characteristics and soil physicochemical properties were measured by field investigation and laboratory analyses, respectively. Soil microbial community composition was determined by high-throughput sequencing techniques. The results showed that there were significant differences in vegetation characteristics, soil physicochemical properties and soil microbial community structure of the planting grassland under different management patterns. Actinobacteria and Basidiomycota were mainly controlled by vegetation plant species diversity, aboveground biomass (AGB) and soil organic carbon (SOC). Shannon-Wiener index, AGB and SOC peaked and the relative abundance of amplicon sequence variants annotated by Actinobacteria and Basidiomycota were significantly enriched under the management pattern of the planting once treatment. Additionally, the soil had the highest bacterial diversity and the lowest fungal diversity under the planting once treatment, becoming a ‘bacterial’ soil. These vegetation characteristics and soil environment were more conducive to overall positive community succession, indicating that the planting once treatment is the most reasonable management pattern for restoring the ‘black beach’.

The Qinghai-Tibetan Plateau (QTP) is generally considered to be the water source region for its surrounding lowlands. However, there have only been a few studies that have focused on quantifying alpine meadow evapotranspiration (ET) and its partitioning, which are important components of water balance. This paper used the Shuttleworth–Wallace (S–W) model to quantify soil evaporation (E) and plant transpiration (T) in a degraded alpine meadow (34°24′ N, 100°24′ E, 3963 m a.s.l) located at the QTP from September 2006 to December 2008. The results showed that the annual ET estimated by the S–W model (ET_SW) was 511.5 mm (2007) and 499.8 mm (2008), while E estimated by the model (E_SW) was 306.0 mm and 281.7 mm for 2007 and 2008, respectively, which was 49% and 29% higher than plant transpiration (T_SW). Model analysis showed that ET, E, and T were mainly dominated by net radiation (R_n), while leaf area index (LAI) and soil water content at a 5 cm depth (SWC_5cm) were the most important factors influencing ET partitioning. The study results suggest that meadow degradation may increase water loss through increasing E, and reduce the water conservation capability of the alpine meadow ecosystem.

Soil carbon (C) and nitrogen (N) have different responses to different restoration measures. In this paper, surface (0-30 cm) soil C and N densities under different restoration measures in the Sanjiangyuan region were investigated and analyzed. The results showed that although there was no significant difference between rest-grazing (RG) and normal grazing (NG) grassland, SOCD in RG increased by 10.15%, and total N density (TND) increased by 8.56% in the year of the experiment. Compared with cropland, 8 years after Grain for Green (GFG), SOCD increased by 10.49-19.31%, SICD increased by 22.47-54.20%, and TND increased by 1.3-17.45%. Compared with HTT (extreme degradation-black soil beach), 12 years after planting artificial grassland, SOCD increased by 43.97-77.21%, SICD increased by 89.19-716.22%, and TND increased by 49.16-71.40%. Conclusions: Differences in soil types and climatic zones were responsible for the differences in soil C and N in different regions. Short-term grazing rest in Sanjiangyuan region has a certain effect on soil fertility restoration. Implementing the GFG project in the agro-pastoral ecotone improved soil fertility and, concurrently, moderate disturbance should be carried out on the basis of increasing vegetation diversity. Artificial grassland planting on black soil beach can improve soil quality, and moderate grazing disturbance in winter had the best immobilization effect on SIC, while no disturbance in the whole year was beneficial to the accumulation of organic matter. Both biological and abiotic factors have affected soil C and N content and density, but the degree of the influence varied with geographic location.