Vegetation influence on the soil hydrological regime in permafrost regions of the Qinghai-Tibet Plateau, China

Soil hydrological processes are extremely complex in high-altitude regions and are recognized to have positive effects on soil quality, nutrient cycling, herbage yield, and runoff generation. However, soil hydrological processes have not been fully quantified in permafrost regions of the Qinghai-Tibet Plateau (QTP). To fill this gap, the soil water dynamics, soil water storage, soil infiltration processes, soil water retention and soil hydraulic conductivity were systematically monitored in different alpine ecosystems (alpine wet meadow (AWM), alpine meadow (AM), and alpine steppe (AS)). The results revealed that the soil water content was significantly higher in AWM soil in the shallow layer, while it was higher in AM soil in the deeper layer. Moreover, the response of soil water to rainfall was markedly more sensitive in AS soil than in AM and AWM soils. The average soil water storage amount reached 440 mm in the 0-100 cm soil interval of the AM, which was nearly 1.6-fold higher than that in the AS and 1.2-fold higher than that in the AWM. The existence of vegetation enhanced the soil infiltration rates in AWM and AM soils 1.3-fold and 1.5-fold, respectively, and decreased the soil infiltration rate 1.2-fold in AS soil. Nuclear magnetic resonance (NMR) results indicated that soil water in AS soil was mainly composed of capillary water and mobile water but was composed of bound water and capillary water in AWM soil and AM soil, respectively. The results from a redundancy analysis (RDA) demonstrated that the vegetation in the study region regulates the soil hydrological regime by altering the soil structure and soil biochemistry. Moreover, the mechanism of vegetation influence on soil hydrological processes suggests that the regional runoff generation will shift with the vegetation succession. The information obtained in this study may aid in the understanding of changes in the ecological environment and regional hydrological cycles under climate change.