Study on recharge source and influence mechanism of plant water in the Three-River Headwaters Region, China

This study, based on the stable isotope tracer technique (delta 18O and delta 2H), focuses on the recharge sources of plant water in the Three-Rivers Headwaters Region in Qinghai province, China. The oxygen and hydrogen isotope signatures of trees and shrubs were more depleted than those of herbs. However, the d-excess pattern was the opposite of the patterns of stable isotopes of oxygen and hydrogen. From the distribution of stable isotope characteristics of water bodies, the direct source of plant water was determined to be soil water, whereas the indirect sources were river water, supra-permafrost water, soil water, precipitation, and ground ice. The contribution proportions of soil water layers between 0 cm and 20 cm and between 40 cm and 60 cm to the plant water were higher than those of other soil water layers for trees. More importantly, the plant water of shrubs was similar to trees in the cold region. The analysis of the indirect recharge sources of plant water revealed that soil water was still the major source of plant water, while glacier snow meltwater, precipitation, and ground ice meltwater are also the main supply sources of plant water. The proportion of supra-permafrost water to plant water was relatively high, mainly because herbs grow in the active layer in the cold region. Therefore, the proportion of plant water recharged by supra-permafrost water and ground ice meltwater was higher than that of other water bodies during the plant growing season.