Patterns and drivers of seasonal water sources for artificial sand-fixing plants in the northeastern Mu Us sandy land, Northwest China

Abstract

Understanding plant water-use patterns is important for improving water-use efficiency and for sustainable vegetation restoration in arid and semi-arid regions. However, seasonal variations in water sources and their control by different sand-fixing plants in water-limited desert ecosystems remain poorly understood. In this study, stable isotopic ratios of hydrogen (δ2H) and oxygen (δ18O) in precipitation, soil water, groundwater, and xylem water were determined to document seasonal changes in water uptake by three representative plant species (Pinus sylvestris var. mongolica Litv., Amygdalus pedunculata Pall., and Salix psammophila) in the northeastern Mu Us sandy land, Northwest China. Based on the depth distribution and temporal variation of measured gravimetric soil water content (SWC), the soil water profile of the three species stands was divided into active (0.01 g g-1 < SWC < 0.08 g g-1, 20% < coefficient of variation (CV) < 45%), stable (0.02 g g-1 < SWC < 0.05 g g-1, CV < 20%), and moist (0.08 g g-1 < SWC < 0.20 g g-1, CV > 45%) layers. Annually, P. sylvestris, A. pedunculata, and S. psammophila obtained most water from deep (59.2% ± 9.7%, moist layer and groundwater), intermediate (57.4% ± 9.8%, stable and moist layers), and shallow (54.4% ± 10.5%, active and stable layers) sources, respectively. Seasonally, the three plant species absorbed more than 60% of their total water uptake from the moist layer and groundwater in the early (June) dry season; then, they switched to the active and stable layers in the rainy season (July–September) for water resources (50.1%–62.5%). In the late (October–November) dry season, P. sylvestris (54.5%–66.2%) and A. pedunculata (52.9%–63.6%) mainly used water from stable and moist layers, whereas S. psammophila (52.6%–70.7%) still extracted water predominantly from active and stable layers. Variations in the soil water profile induced by seasonal fluctuations in precipitation and groundwater levels and discrepancies in plant phenology, root distribution, and water demand are the main factors affecting the seasonal water-use patterns of artificial sand-fixing plants. Our study addresses the issue of plant water uptake with knowledge of proportional source-water use and reveals important implications for future vegetation restoration and water management in the Mu Us sandy land and similar desert regions around the world.