Seasonal Dynamics of Water Use Strategy of Two Salix Shrubs in Alpine Sandy Land, Tibetan Plateau.

Yajuan Zhu,Guojie Wang,Renqiang Li

doi:10.1371/journal.pone.0156586

Abstract

Water is a limiting factor for plant growth and vegetation dynamics in alpine sandy land of the Tibetan Plateau, especially with the increasing frequency of extreme precipitation events and drought caused by climate change. Therefore, a relatively stable water source from either deeper soil profiles or ground water is necessary for plant growth. Understanding the water use strategy of dominant species in the alpine sandy land ecosystem is important for vegetative rehabilitation and ecological restoration. The stable isotope methodology of δD, δ18O, and δ13C was used to determine main water source and long-term water use efficiency of Salix psammophila and S. cheilophila, two dominant shrubs on interdune of alpine sandy land in northeastern Tibetan Plateau. The root systems of two Salix shrubs were investigated to determine their distribution pattern. The results showed that S. psammophila and S. cheilophila absorbed soil water at different soil depths or ground water in different seasons, depending on water availability and water use strategy. Salix psammophila used ground water during the growing season and relied on shallow soil water recharged by rain in summer. Salix cheilophila used ground water in spring and summer, but relied on shallow soil water recharged by rain in spring and deep soil water recharged by ground water in fall. The two shrubs had dimorphic root systems, which is coincident with their water use strategy. Higher biomass of fine roots in S. psammophila and longer fine roots in S. cheilophila facilitated to absorb water in deeper soil layers. The long-term water use efficiency of two Salix shrubs increased during the dry season in spring. The long-term water use efficiency was higher in S. psammophila than in S. cheilophila, as the former species is better adapted to semiarid climate of alpine sandy land.

Highlights

The alpine sandy land of Gonghe Basin is located in the northeastern Tibetan Plateau, which is an ecotone from semi-arid steppe to arid desert steppe and with the altitude ranging from 2600 m to 3400 m
S. cheilophila used shallow soil water recharged by rain at a soil depth of 10–25 cm and ground water in spring, soil water at a soil depth of 10–200 cm and ground water in summer, and deep soil water recharged by ground water at a soil depth of 100–200 cm in fall (Fig 5, Table 2)
In alpine sandy land of the Tibetan Plateau, S. psammophila and S. cheilophila growing on the interdune used soil water at different soil depths or ground water, depending on water availability in the growing season

Summary

Introduction

The alpine sandy land of Gonghe Basin is located in the northeastern Tibetan Plateau, which is an ecotone from semi-arid steppe to arid desert steppe and with the altitude ranging from 2600 m to 3400 m. It is one of the most severely desertified area in Qinghai Province [1]; desertification is mainly caused by climate change [2] and human activities [3]. Trees from the genus Populus were planted inside oasis, Salix shrubs were planted on interdune, and shrubs from the genus Caragana were planted on sand dunes This approach was successful as the shelterbelt system decreased sand storms and improved microclimate [4]. The stable water source from either deep soil profiles or ground water is necessary for plant growth especially under drought conditions [11]

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Conclusion