Response of dew and hydraulic redistribution to soil water in a rainfed dryland jujube plantation in China’s Hilly Loess Region

Abstract

Soil desiccation occurs widely across China’s Loess Plateau due to long-term water demand in excess of water supply. Hydraulic redistribution (HR) - the movement of water from wet to dry soil via roots - and canopy dew (CD) are crucial to water replenishment in dryland ecosystems. However, much is still not known about the response of CD and HR to soil water deficits (including no deficit, slight deficit, moderate deficit, and severe deficit water conditions) in dryland jujube (Ziziphus jujuba Mill.) plantations in China’s Hilly Loess Region. To this end, the duration and intensity of dew were monitored using dielectric leaf wetness sensors to better understand the effects of soil water status on dew. Also, soil water content, sap flow, and meteorological variables were measured during the jujube growing seasons in 2017–2019. The results showed that the time of occurrence of CD under the no deficit condition came earlier than the time of occurrence of CD under slight, moderate, and severe soil water deficit conditions. Peak CD appeared at 5:00–6:30 am and ended at 6:30–9:00 am local time under the four soil water conditions. The amount, duration, and frequency of CD decreased with increasing soil water deficit. The amount and duration of CD under the no deficit condition were significantly higher than under the slight, moderate, and severe soil water deficit conditions (p < 0.05). The amount and frequency of HR (in the 20–60 cm soil layer) increased with increasing soil water deficit. Under the no deficit condition, HR was significantly lower than under the slight, moderate, and severe soil water deficit conditions (p < 0.05). While HR was influenced by CD, CD enhanced HR under the no deficit condition, but inhibited HR under slight, moderate, and severe soil water deficit conditions. For the growing season, the contribution of CD to total actual evapotranspiration (ETc act, CD/ ETc act ratio) was highest under the no deficit condition (maximum CD/ ETc act ratio of 0.21). The contribution of HR to ETc act (HR/ ETc act ratio) was higher under slight, moderate, and severe soil water deficit conditions (maximum of 0.11). The mutual effects of CD and HR lessened soil water deficit, making them important ecohydrological processes affecting the response of dryland jujube plantations to soil desiccation.