Effects of degradation degree on plant communities and soil water holding capacity of Maqin alpine meadow

To explore the influence of the degree of degradation on the success of plant communities and the water conservation capacity of alpine meadows in the Three Rivers Source Region, this study selected Maqin alpine meadow sample land with different degradation degrees in the source area of the Three Rivers on the Qinghai-Tibet Plateau. Through a combination of field monitoring and indoor tests, this study analyzed the effects of different degradation degrees on plant coverage, height, species number, biomass, soil bulk density, soil saturated hydraulic conductivity, and water holding capacity. The results showed the following: 1) The alpine meadow is in the process of continuous degradation, and the average height and coverage of plants in the Maqin alpine meadow decreased significantly by 41.1% and 58.5%, respectively (P < 0.05); the species number, richness, diversity index, and evenness index of vegetation decreased gradually, and the dominance index was the highest (0.18) in mildly degraded plots. 2) The aboveground, belowground, and total biomass decreased significantly with an increase in the degree of degradation (P < 0.05). Compared with the original vegetation sample plot, the aboveground, underground, and total biomass decreased by 49.8%, 71.1%, and 70.0%, respectively. 3) The effect of the degree of degradation on the soil water holding capacity and saturated water conductivity of alpine meadows decreased with increasing depth, and the effect on soil water holding capacity and saturated water conductivity of the surface layer (0 − 5 cm) was the most significant. Compared with the native vegetation, the 0 − 5 cm soil water capacity, field water capacity, capillary water capacity, and saturated water conductivity of the severely degraded alpine meadow decreased by 41.7%, 42.9%, 41.4%, and 84.4%, respectively. With an increase in the degree of degradation, the soil bulk density of the 0 − 5 cm soil layer of alpine meadow increased significantly (P < 0.05). In conclusion, as the degree of degradation increased, the species richness, diversity, evenness, and dominance of alpine meadow vegetation communities decreased. At the same time, the influence of the degree of degradation on the soil water holding capacity of alpine meadows is primarily concentrated in the 0 − 5 cm layer, and the surface matting of alpine meadows is the key to maintaining the water conservation function of this region.