Stable Isotopic Analysis on Water Utilization of Two Xerophytic Shrubs in a Revegetated Desert Area: Tengger Desert, China

Lei Huang,Zhishan Zhang

doi:10.3390/w7031030

Abstract

Stable isotope studies on stable isotope ratios of hydrogen and oxygen in water within plants provide new information on water sources and water use patterns under natural conditions. In this study, the sources of water uptake for two typical xerophytic shrubs, Caragana korshinskii and Artemisia ordosica, were determined at four different-aged revegetated sites (1956, 1964, 1981, and 1987) in the Tengger Desert, a revegetated desert area in China. Samples from precipitation, soil water at different soil layers, and xylem water from each species were collected in 2013. The proportion of plant water sources derived from different potential sources was determined using oxygen (δ18O) and hydrogen (δD) stable isotope analysis combined with a multiple-source linear mixing model. Results showed that the local meteoric water line (LMWL) at Shapotou was as follows: δD = 7.39δ18O + 3.91 (R2 = 0.93; n = 26). The vertical distribution of soil water content in older vegetation areas (1956a and 1964a) was much lower than that in relatively younger vegetation areas (1981a and 1987a). Mean soil water δD and δ18O values varied with depth, and the variation decreased as the age of the revegetated site increased. In general, C. korshinskii and A. ordosica mainly tapped water from the upper soil layer (10–100 cm) during the wet seasons. With increasing sand stabilization age, the proportion of water sources from shallow soil water decreased, whereas deep soil moisture utilization increased. During the dry season, C. korshinskii and A. ordosica showed evident hierarchical utilization of soil water in different soil layers. Small rainfall events did not significantly affect the water source of C. korshinskii and A. ordosica. However, large rainfall events not only complemented the deep soil moisture, but also recharged the shallow soil water after a few days, and the proportion of soil water source from deep soil layer increased from 2% ± 0.7% to 10% ± 1.4% for both plants.

Highlights

In arid desert areas, artificial vegetation restoration is considered as one of the most effective ways to combat desertification and land degradation [1,2]
To specify the mechanism by which water sources of C. korshinskii and A. ordosica plants are affected by precipitation, we examined two specific cases under natural conditions: water uptake characteristics following a small rain event (1.4 mm; Figure 4A–C), and water uptake characteristics following a large rain event (12.2 mm; Figure 4D–F)
The lower slope and intercept of the GMWL suggest the occurrence of substantial soil evaporation enrichments relative to rainwater [30]; these parameters show a close correlation between xylem water supplies of C. korshinskii and A. ordosica

Summary

Introduction

Artificial vegetation restoration is considered as one of the most effective ways to combat desertification and land degradation [1,2]. Xerophytic shrubs, such as Caragana korshinskii Kom. and Artemisia ordosica Krasch, have been planted at the southeastern fringe of the Tengger Desert in Western China since 1956. A number of problems have been observed in practice, such as a decline in groundwater and the death of sand-binding vegetation in some regions, thereby directly effecting the sustainability of the ecological restoration and the sand-binding efficiency of the vegetation [4]. Water is the key abiotic limiting factor in ecosystem-driven processes, and precipitation, as the sole source of soil water replenishment in the Tengger Desert, plays an important role in sustaining the desert ecosystem, determining the mass transfer process in the soil and vegetation ecosystem [4]

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Conclusion