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Plant Physiol. 2019 Apr;179(4):1658-1668. doi: 10.1104/pp.18.01303. Epub 2019 Feb 4.

Spatiotemporal Coupling of Vessel Cavitation and Discharge of Stored Xylem Water in a Tree Sapling.

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Department of Viticulture and Enology, University of California, Davis, California 95616.
School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut 06511.
Schmid College of Science and Technology, Chapman University, Orange, California 92866.
Warnell School of Forestry and Natural Resources, University of Georgia, Athens, Georgia 30602.
Department of Viticulture and Enology, University of California, Davis, California 95616
U.S. Department of Agriculture-Agricultural Research Service, Crops Pathology and Genetics Research Unit, Davis, California 95618.


Water discharge from stem internal storage compartments is thought to minimize the risk of vessel cavitation. Based on this concept, one would expect that water storage compartments involved in the buffering of xylem tensions empty before the onset of vessel cavitation under drought stress, and potentially refill after soil saturation. However, scant in vivo data exist that elucidate this localized spatiotemporal coupling. In this study on intact saplings of American chestnut (Castanea dentata), x-ray computed microtomography (microCT) showed that the xylem matrix surrounding vessels releases stored water and becomes air-filled either concurrent to or after vessel cavitation under progressive drought stress. Among annual growth rings, the xylem matrix of the current year remained largely water-filled even under severe drought stress. In comparison, microtomography images collected on excised stems showed that applied pressures of much greater than 0 MPa were required to induce water release from the xylem matrix. Viability staining highlighted that water release from the xylem matrix was associated primarily with emptying of dead fibers. Refilling of the xylem matrix and vessels was detected in intact saplings when the canopy was bagged and stem water potential was close to 0 MPa, and in leafless saplings over the winter period. In conclusion, this study indicates that the bulk of water stored in the xylem matrix is released after the onset of vessel cavitation, and suggests that capillary water contributes to overall stem water storage under drought but is not used primarily for the prevention of drought-induced vessel cavitation in this species.

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