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Title: Spatiotemporal coupling of vessel cavitation and discharge of stored xylem water in a tree sapling

Author
item KNIPFER, THORSTEN - University Of California
item REYES, CLARISSA - University Of California
item EARLES, J. MASON - Yale University
item BERRY, Z. CARTER - Chapman University
item JOHNSON, DAN - University Of Georgia
item BRODERSEN, CRAIG - Yale University
item McElrone, Andrew

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2019
Publication Date: 2/4/2019
Citation: Knipfer, T., Reyes, C., Earles, J., Berry, Z., Johnson, D., Brodersen, C., McElrone, A.J. 2019. Spatiotemporal coupling of vessel cavitation and discharge of stored xylem water in a tree sapling. Plant Physiology. 179:1658-1668. https://doi.org/10.1104/pp.18.01303.
DOI: https://doi.org/10.1104/pp.18.01303

Interpretive Summary:

Technical Abstract: 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 empty prior to vessel cavitation under drought stress and refill following soil saturation. However, scant in-vivo data exist that elucidate the localized spatiotemporal coupling between both physiological processes in an intact woody plant. In this study on 2-year old intact saplings of Castanea dentata, X-ray computed microtomography (microCT) imaging showed that the xylem matrix surrounding vessels releases stored water (i.e. becomes air-filled) either together or following vessel cavitation and bark shrinkage under progressive drought stress. Among annual growth rings, the xylem matrix of the current year remained largely water-filled even under severe drought stress and at a stem water potential of <<-1MPa. In-vivo refilling of both xylem matrix and vessels was observed but only occurred when stem water potential approached 0 MPa pointing to a strong hysteresis in the xylem emptying-refilling process in relation to existing xylem tensions. In line with observations on intact saplings, microCT images collected on excised stems showed that relatively high pressures were required to induce water release from the xylem matrix which dominated the second phase of the biphasic water-release curve. In conclusion, this in-vivo study indicates that the bulk of water stored in dead cells of the xylem matrix is not utilized for the prevention of drought-induced vessel cavitation and appears to be largely disconnected from drought-induced changes in xylem tensions within the transpiration stream.