Water uptake can occur through woody portions of roots and facilitates localized embolism repair in grapevine

Authors: CUNEO, ITALO - University Of California; KNIPFER, THORSTEN - University Of California; MANDAL, PRATITI - Lawrence Berkeley National Laboratory; BRODERSEN, CRAIG - Yale University; McElrone, Andrew

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2017
Publication Date: 2/20/2018
Citation: Cuneo, I., Knipfer, T., Mandal, P., Brodersen, C., McElrone, A.J. 2018. Water uptake can occur through woody portions of roots and facilitates localized embolism repair in grapevine. New Phytologist. 218(2):506-516. https://doi.org/10.1111/nph.15032.
DOI: https://doi.org/10.1111/nph.15032

Interpretive Summary: Water acquisition is thought to be limited to the unsuberized surface located close to root tips. However, there are recurring periods when the unsuberized surfaces are limited in woody root systems, and radial water uptake across the bark of woody roots might play an important physiological role in hydraulic functioning. Using X-ray microcomputed tomography (microCT) and hydraulic conductivity measurements (Lpr), we examined water uptake capacity of suberized woody roots in vivo and in excised samples. Bark hydration in grapevine woody roots occurred quickly upon exposure to water (c. 4 h). Lpr measurements through the bark of woody roots showed that it is permeable to water and becomes more so upon wetting. After bark hydration, microCT analysis showed that absorbed water was utilized to remove embolism locally, where c. 20% of root xylem vessels refilled completely within 15 h. Embolism removal did not occur in control roots without water. Water uptake through the bark of woody roots probably plays an important role when unsuberized tissue is scarce/absent, and would be particularly relevant following large irrigation events or in late winter when soils are saturated, re-establishing hydraulic functionality before bud break.

Technical Abstract: Woody root systems can be quite extensive by spreading both laterally and deeply. The vast majority of surface area for woody root systems is suberized (i.e. covered with bark), and assumed to function exclusively in anchorage, storage, and vascular transport, Resource acquisition is thought to be limited to the unsuberized surface located close to the root apices, however, there are recurring periods when these surfaces are limited in woody roots systems (e.g. died off or became suberized). This suggests that water uptake through the bark of woody roots becomes important during some periods of the growing season. Using X-ray micro-computed tomography (microCT), we found that bark hydration in excised woody roots of grapevine happens very quickly upon exposure to water (~4 h). Measurements of radial hydraulic conductivity (Lpr) through the bark of woody roots showed that these root portions are hydraulically permeable, become more permeable upon wetting, and likely play an important role in water uptake when unsuberized tissue is scarce or absent. After bark hydration, microCT analysis showed that absorbed water is utilized to remove embolism locally, where ~20% of root xylem vessels refilled completely within 15 h. Embolism repair did not repair in control roots without water. Observations of water uptake through the bark of woody roots could be important when soils are saturated following large winter rainfall or irrigation events, and aid in the generation of spring root pressure or to facilitate freeze-thaw induced embolism repair.