Intensification of water storage deficit in topsoil but not deep soil in a semi-humid forest after excluding precipitation for two years

Abstract

Deep-rooted forest trees can potentially utilize moisture in deep soil to tolerate periods when growth is water limited. Black locust (R. pseudoacacia) is a deep-rooted forest species but the benefits of deep roots for water uptake under drought conditions are unclear. In this study, we assessed the effects of drought on water storage and the hydrological properties of soil at different depths. We performed a precipitation manipulation experiment continuously from June 2015 to November 2016 using mature R. pseudoacacia in the Loess Plateau region of China. The soil volumetric water contents were measured in the 0–4 m soil layer, as well as the soil hydrological properties comprising the soil bulk density (BD), total porosity, saturated hydraulic conductivity (Ks), and aggregate-associated organic carbon (OC) concentration in the 0–20 cm soil layer. The results showed that soil water storage deficit mainly occurred in the 0–1 m soil layer rather than in the 1–4 m layer after excluding precipitation for two years. Compared with the control, excluding precipitation for two years decreased the soil water storage in the 0–1 m soil layer by 18%. Precipitation exclusion also significantly decreased the soil Ks by 28% and total porosity by 17%, but increased BD by 20% in the 0–10 cm soil layer. In addition, precipitation exclusion significantly decreased the total soil OC concentration and macro- and micro-associated OC concentrations. Our results indicate that excluding precipitation for two years could potentially degrade the water conditions in the topsoil layer but not the deeper soil. These findings provide insights into water management and sustainability in semi-humid afforestation areas of the Loess Plateau region in China.