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 to 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.

Principal Investigator

Jeffrey Warren
Oak Ridge National Laboratory
warrenjm@ornl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

Support from Laboratory Directed Research and Development Program at Oak Ridge National Laboratory (ORNL); Office of Biological and Environmental Research within the U.S. Department of Energy (DOE) Office of Science; DOE Office of Science’s Office of Workforce Development for Teachers and Scientists; Office of Science Graduate Student Research (SCGSR) program; High Flux Isotope Reactor (HFIR), a DOE Office of Science user facility operated by ORNL.

References