Climate,vegetation, and soil controls on hydraulic redistribution in shallow tree roots |
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| Institution: | 1. Lushan National Observation and Research Station of Chinese Forest Ecosystem, Key Laboratory of National Forestry and Grassland Administration on Forest Ecosystem Protection and Restoration of Poyang Lake Watershed, Jiangxi Agricultural University, Nanchang 330045, China;2. Beijing Forestry University, Key Laboratory of Soil and Water Conservation and Desertification Combating of Ministry of Education, 100083 Beijing, China;3. College of Forestry, Central South University of Forestry and Technology, Changsha 410004, China;4. Lushan Nature Reserve of Jiangxi (Lushan Mountain National Forest Ecological Station), Henan Rd. 600, Jiujiang 332900, PR China |
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| Abstract: | Hydraulic redistribution defined as the translocation of soil moisture by plant root systems in response to water potential gradients is a phenomenon widely documented in different climate, vegetation, and soil conditions. Past research has largely focused on hydraulic redistribution in deep tree roots with access to groundwater and/or winter rainfall, while the case of relatively shallow (i.e., ≈1–2 m deep) tree roots has remained poorly investigated. In fact, it is not clear how hydraulic redistribution in shallow root zones is affected by climate, vegetation, and soil properties. In this study, we developed a model to investigate the climate, vegetation, and soil controls on the net direction and magnitude of hydraulic redistribution in shallow tree root systems at the growing season to yearly timescale. We used the model to evaluate the effect of hydraulic redistribution on the water stress of trees and grasses. We found that hydraulic lift increases with decreasing rainfall frequency, depth of the rooting zone, root density in the deep soil and tree leaf area index; at the same time for a given rainfall frequency, hydraulic lift increases with increasing average rainstorm depth and soil hydraulic conductivity. We propose that water drainage into deeper soil layers can lead to the emergence of vertical water potential gradients sufficient to explain the occurrence of hydraulic lift in shallow tree roots without invoking the presence of a shallow water table or winter precipitation. We also found that hydraulic descent reduces the water stress of trees and hydraulic lift reduces the water stress of grass with important implications on tree–grass interactions. |
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| Keywords: | Hydraulic redistribution Shallow tree roots Climate Vegetation Soil properties Water stress |
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