Variations in capacity and storage of plant-available water in deep profiles along a revegetation and precipitation gradient

Abstract

Knowledge of regional characteristics and variability in available soil water is important for water resource management and vegetation restoration in arid and semi-arid regions. However, few studies have evaluated the available water-holding capacity (AWHC) and plant-available water storage (PAWS) for plant growth or determined the saturation of available soil water (SASW) in deep profiles (>2 m). This study investigated characteristics of AWHC and PAWS to a depth of 5 m along a revegetation and precipitation gradient on the Chinese Loess Plateau (CLP). The results showed that AWHC5 m exhibited a decreasing trend along the transect, with a mean value of 762.9 mm. PAWS5 m first decreased, then increased following changes in vegetation types with a mean value of 257.3 mm. The PAWS5 m significantly differed under different soil layers and showed high variation (coefficient of variation = 88.0%) in its profile. AWHC5 m was significantly correlated with all environmental factors except slope aspect and slope gradient. A comparative analysis showed that PAWS5 m had a small portion of AWHC5 m, both of which varied among different vegetation species. Variations in PAWS5 m and AWHC5 m were higher in the 450–550 mm precipitation zone and silt loam soil. Planted forests with deep root systems introduced in the 450–550 mm precipitation zone had lower SASW5 m values than the areas with shallow root vegetation. A complete understanding of the spatial variations of PAWS, AWHC, and SASW along the revegetation and precipitation gradient will be helpful in assessing regional water resources and optimizing vegetation species on the CLP and possibly in other water-limited regions around the world.