U.S. Department of Energy Office of Biological and Environmental Research

PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

Using neutron imaging to measure and modeling poplar root water extraction after drought

Jeffrey M Warren
Oak Ridge National Laboratory

Highlight

Roots and relative water content of an 11-week old poplar tree seedling growing in sand inside an aluminum chamber. The image is a color enhanced neutron radiograph from research at the High Flux Isotope Reactor at Oak Ridge National Laboratory. Blue and yellow colors indicate greater water content, red indicates lower water content.

11 September 2017

Linking root water uptake to root traits, and assessing (poor) performance of common models

The Science
Neutron imaging is used to measure soil water movement and water uptake by individual roots in situ.

The Impact
Root water uptake can be linked to characteristic root traits, such as diameter or age. Comparing actual water uptake with modeled water uptake highlights problems with current model assumptions. This work points to the need for new research to understand soil hydraulic properties with and without roots present.

Summary
Knowledge of plant root function is largely based on indirect measurements of bulk soil water or nutrient extraction, which limits modeling of root function in land surface models. Neutron radiography, complementary to X-ray imaging, was used to assess in situ water uptake from newer, finer roots and older, thicker roots of a poplar seedling growing in sand. The smaller diameter roots had greater water uptake per unit surface area than the larger diameter roots, ranging from 0.0027-0.0116 g/cm2 root surface area/h. Model analysis based on root-free soil hydraulic properties indicated unreasonably large water fluxes between the vertical soil layers during the first 16 hours after wetting — suggesting problems with common soil hydraulic or root surface area modeling approaches, and the need to further research and understand the impacts of roots on soil hydraulic properties.

Contacts
(BER PM)

Daniel Stover
Daniel.Stover@science.doe.gov (301-903-0289)

Roland Hirsch
Roland.Hirsch@science.doe.gov (301-903-9009)

(PI Contact)
Jeffrey M Warren
Environmental Sciences Division and Climate Change Science Institute, Oak Ridge National Laboratory
warrenjm@ornl.gov (865-241-3150)

Funding
Laboratory Directed Research and Development Program at Oak Ridge National Laboratory (ORNL). DOE, Office of Science, Office of Biological and Environmental Research, Office of Workforce Development for Teachers and Scientists and Office of Science Graduate Student Research (SCGSR) program. High Flux Isotope Reactor, a DOE Office of Science User Facility operated by ORNL

Publications
Dhiman, I, H Bilheux, K DeCarlo, SL Painter, L Santodonato, JM Warren (2017) “Quantifying root water extraction after drought recovery using sub-mm in situ empirical data,” Plant and Soil [doi.org/10.1007/s11104-017-3408-5].

Funded by the Terrestrial Ecosystem Sciences Science Focus Area: “Root Function”, Biological and Environmental Research Program in the Office of Science, U.S. Department of Energy, and by the Office of Science, Office of Workforce Development for Teachers and Scientists, Graduate Student Research (SCGSR) program, the LDRD Program at Oak Ridge National Laboratory. Measurements were performed at the Oak Ridge National Laboratory's High Flux Isotope Reactor (HFIR) CG-1D imaging beamline.

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