Spatiotemporal variation of soil water potential and its significance to water balance for a desert shrub area

In dry sandy soil, soil water is naturally redistributed by forces owing to matric and gravitational potential, and temperature gradients. Occurring shrub vegetation strongly influences these patterns by hydraulic redistribution within the soil. This means that plants can move water from moist to drier soil areas to extract nutrients from the drier soil and enhance nutrient uptake. This incorporates both upward and downward transport of water through the roots. Diel soil water potential (ψs) and soil temperature fluctuation were investigated at 30-min intervals for a respectively vegetated desert shrub area and non-vegetated bare area. Soil water potential fluctuations at the vegetated area reflected daytime depletion and nocturnal re-supply of water due to hydraulic redistribution while corresponding fluctuations at the non-vegetated area were mainly due to variation in soil temperature. Thus, the greatest diel ψs variability occurred in the vegetated area that averaged −0.401 MPa with a smaller variation in the non-vegetated area with an average of −0.009 MPa. At the shrub scale, ψs was strongly correlated with root distribution pattern that corroborates that diel variation in the active root zone of the shrub was mainly attributed to hydraulic redistribution. In the non-vegetated area, ψs responded more strongly to temperature gradients. The total of hydraulic redistribution of soil water storage increment accounted for 27 % of the total rainfall through the growing season from April to September. The study shows that it is important to consider biotic-factors such as hydraulic redistribution when analyzing water balance changes and hydrological niche segregation for desert ecosystems.