Chengyi Li

This study aims to enlighten our understanding of the distribution of soil carbon-fixing bacteria (cbbL-harboring bacteria) and their community diversity in differently degraded patches at three altitudes. MiSeq high-throughput sequencing technology was used to analyze the soil carbon-fixing bacteria community diversity of degraded patches and healthy meadow at three altitudes. Redundancy analysis (RDA) and structural equation model (SEM) were used to analyze the correlation and influence path between environmental factors and carbon-fixing bacteria. The results showed that degradation reduced the relative abundance of Proteobacteria from 99.67% to 95.57%. Sulfurifustis, Cupriavidus, and Alkalispirillum were the dominant genera at the three altitudes. Hydrogenophaga and Ectothiorhodospira changed significantly with altitude. RDA results confirmed that available phosphorus (AP) was strongly and positively correlated with Proteobacteria. AP and total nitrogen (TN) were strongly and positively correlated with Hydrogenophaga. Grass coverage and sedge aboveground biomass were strongly and positively correlated with Sulfurifustis and Ectothiorhodospira, respectively. Elevation adversely affected the relative abundance of dominant carbon-fixing bacteria and diversity index by reducing the coverage of grass and soil volumetric moisture content (SVMC) indirectly, and also had a direct positive impact on the Chao1 index (path coefficient = 0.800). Therefore, increasing the content of nitrogen, phosphorus and SVMC and vegetation coverage, especially sedge and grass, will be conducive to the recovery of the diversity of soil carbon-fixing bacteria and improve the soil autotrophic microbial carbon sequestration potential in degraded meadows, especially in high-altitude areas.

In this study, we analyzed the C, N, and P contents and stoichiometric characteristics of forage leaves of five species (Elymus breviaristatus cv. Tongde, Poa crymophila cv. Qinghai, Puccinellia tenuiflora cv. Qinghai, Festuca sinensis cv. Qinghai, and Poa pratensis cv. Qinghai) in “fertilizer-reconstructed soil” through integrative soil amendment with parched sheep manure and granular organic fertilizer in an alpine mining area. A model is fitted in order to screen out the best forage species suitable for vegetation restoration in the alpine mining area and the most favorable fertilizer dosage to improve the nutrient content of forage leaves. The results showed that (1) increasing the dosages of granular organic fertilizer and sheep manure had little effect on the C content of the five types of forage grasses, but they could significantly increase the N and P contents and N/P of the manually restored grassland in the alpine mining area (p < 0.05). (2) The productivity and stability of the five species were ranked as follows: Elymus breviaristatus cv. Tongde > Puccinellia tenuiflora cv. Qinghai > Festuca sinensis cv. Qinghai > Poa pratensis cv. Qinghai > Poa crymophila cv. Qinghai. (3) According to the fitted least squares model and the willingness to maximize the C, N, and P contents of the leaves, the ranking of the five forage grasses was described by the Prediction Profiler as follows: Elymus breviaristatus cv. Tongde > Puccinellia tenuiflora cv. Qinghai > Festuca sinensis cv. Qinghai > Poa crymophila cv. Qinghai > Poa pratensis cv. Qinghai. (4) The predictive model suggested that the optimal contents of C, N, and P in Elymus breviaristatus cv. Tongde, Festuca sinensis cv. Qinghai, and Poa pratensis cv. Qinghai leaves could be achieved with the application of 3.6 kg/m² of granular organic fertilizer and 45.0 kg/m² of sheep manure. For Poa crymophila cv. Qinghai leaves, the ideal content was attained by applying 0 kg/m² of granular organic fertilizer and 45.0 kg/m² of sheep manure. Lastly, the optimal C, N, and P contents in Puccinellia tenuiflora cv. Qinghai leaves could be obtained through the application of 3.6 kg/m² of granular organic fertilizer combined with 0 kg/m² of sheep manure. In conclusion, the study’s results highlight the significant practical value of the fertilizer-reconstructed soil for vegetation restoration in alpine mining regions.

This study aimed to understand the response of vegetation community characteristics in the degraded alpine meadow of the Source Zone of the Yellow River to exclosure of various lengths. Artificial fences were erected to prevent livestock grazing and let the degraded meadow recover naturally as a means of restoration. The research focused on a typical degraded alpine meadow in which four plots were fenced off for three periods of 1 year (E1), 4 years (E4), and 10 years (E10), plus a freely grazed plot as the control. The study compared and analyzed the differences in plant community characteristics, carbon (C), nitrogen (N), and phosphorus (P) reserves, as well as the stoichiometric characteristics of main functional groups in the alpine meadow over different exclosure durations. The results indicated that E10 long-term exclosure significantly increased the aboveground biomass of gramineous plants but reduced the aboveground biomass of miscellaneous grasses. However, when compared to E4 short-term exclosure, E10 resulted in a reduction in the aboveground biomass of Cyperaceae plants. On the other hand, E4 medium-term exclosure significantly increased the aboveground biomass of Gramineae and Cyperaceae. Exclosure significantly increased the nitrogen (N) and phosphorus (P) reserves of the aboveground plant communities. Among these communities, the plant communities in the E10 long-term exclosure had the highest N and P reserves. However, this exclosure length also led to a significant reduction in plant diversity. Furthermore, except for Cyperaceae, all functional groups were observed in E10 and E4 plots. The carbon–nitrogen ratio and carbon–phosphorus ratio of these groups were significantly lower than those of groups G and E1. Medium-term exclosure (E4) has a positive impact on the aboveground biomass as well as plants’ nitrogen and phosphorus reserves. However, long-term exclosure (E10) has been observed to decrease species diversity and nutrient utilization efficiency of alpine meadow vegetation, which can be detrimental to the sustainable development of the alpine meadow ecosystem. Therefore, it is not recommended to implement long-term exclosure. Instead, a moderate level of grazing should be adopted after 4 years of exclosure.

Plant diversity plays an important role in maintaining the stability of ecosystem functioning. Based on field surveys and indoor analyses, this study investigated the relationship between species diversity and community stability at different stages of bare patch succession in degraded alpine meadow ecosystems. Results show that: (1) Using the ICV (the Inverse of the Coefficient of Variation) method to analyze changes in plant community stability, community stability was generally ranked as follows: Long-term recovered patches > Healthy alpine meadow > Degraded alpine meadow > Short-term recovered patch > Bare Patches. (2) Using factor analysis to construct an evaluation system, the stability ranking based on species diversity was as follows: Healthy alpine meadow > Long-term recovered patches > Degraded alpine meadow > Short-term recovered patches > Bare Patches. (3) The community stability index was significantly positively correlated with vegetation coverage, height, biomass, species richness, Shannon–Wiener diversity index, species evenness, and Simpson’s diversity index (p < 0.05). Therefore, a positive correlation exists between plant diversity and community stability, such that plant communities with a higher species diversity tend to be more stable. To maintain the plant diversity and community stability of alpine meadow ecosystems, it is necessary to consider the characteristics of grassland plant composition and community structure, as well as their influencing factors, and promote the positive succession process of grasslands.

Identifying the relative contributions of climate change and human activities to alpine grassland dynamics is critical for understanding grassland degradation mechanisms. In this study, first, the actual NPP (NPP_a) was obtained by MOD17A3. Second, we used the Zhou Guangsheng model to simulate the potential met net primary productivity (NPP_p). Finally, the NPP generated by anthropogenic activities (NPP_h) was estimated by calculating the difference between NPP_p and NPP_a. Then, the relative contributions of climate change and human activities to NPP changes in grasslands were quantitatively assessed by analyzing trends in NPP_p and NPP_a. Thereby, the drivers of NPP change in the Yellow River source grassland were identified. The results showed that the temperature and precipitation in the study area showed a warm-humid climate trend from 2000 to 2020. The NPP_p and NPP_a increased at a rate of 1.07 g C/m² and 1.51 g C/m² per year, respectively, while the NPP_h decreased at a rate of 0.46 g C/m² per year. It can be seen that human activities had a positive effect on the change of NPP in the Yellow River source grassland from the change rate. The relative contribution analysis showed that 55.90% of grassland NPP increased due to climate change, 40.16% of grassland NPP increased due to human activities, and the grassland degradation was not significant. The research results can provide a theoretical basis and technical support for the next step of the Yellow River source grassland ecological protection project.