Quantifying root water extraction after drought recovery using sub-mm in situ empirical data
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Root-specific responses to stress are not well-known, and have been largely based on indirect measurements of bulk soil water extraction, which limits mechanistic modeling of root function.
Here, we used neutron radiography to examine in situ root-soil water dynamics of a previously droughted black cottonwood (Populus trichocarpa) seedling, contrasting water uptake by the two major components of the root system that differed in initial recovery rate as apparent by ‘new’ (whiter, thinner), or ‘old’ (darker, thicker) parts of the fine root system.
The smaller diameter ‘new’ roots had greater water uptake per unit surface area than the larger diameter ‘old’ roots, but they had less total surface area leading to less total water extraction; rates ranged from 0.0027–0.0116 g cm−2 h−1. The finest most-active roots were not visible in the radiographs, indicating the need to include destructive sampling. Analysis based on root-free bulk soil hydraulic properties indicated substantial redistribution of water via saturated/unsaturated flow and capillary wicking across the layers - suggesting water uptake dynamics following an infiltration event may be more complex than approximated by common soil hydraulic or root surface area modeling approaches.
Our results highlight the need for continued exploration of root-trait specific water uptake rates in situ, and impacts of roots on soil hydraulic properties – both critical components for mechanistic modeling of root function.
KeywordsNeutron radiography Modeling Populus Hydraulic redistribution Rhizosphere Water uptake
We thank Deanne Brice for plant propagation and root analysis. Research sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory (ORNL), managed by UT-Battelle, LLC, for the U. S. Department of Energy (DOE), by the DOE Office of Science, Office of Biological and Environmental Research, and by the DOE, Office of Science, Office of Workforce Development for Teachers and Scientists, Office of Science Graduate Student Research (SCGSR) program. The SCGSR program is administered by the Oak Ridge Institute for Science and Education (ORISE) for the DOE. ORISE is managed by ORAU under contract number DE-AC05-06OR23100. ORNL is managed by UT-Battelle, LLC, for the DOE under contract DE-AC05-1008 00OR22725. This research used resources at the High Flux Isotope Reactor, a DOE Office of Science User Facility operated by ORNL.
This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the US Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).
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