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Title:   Author  item
                                            CHOAT, BRENDAN - Western Sydney Universityitem
                                            BRODERSEN, CRAIG - Yale Universityitem
                                            McElrone, Andrew
  Submitted to: New Phytologist
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 11/10/2014
                                    Publication  Date: 2/10/2015
                                    Publication URL: http://onlinelibrary.wiley.com/doi/10.1111/nph.13110/abstractCitation: Choat, B., Brodersen, C., Mcelrone, A.J. 2015. Synchrotron microtomography of xylem embolism in Sequoia sempervirens seedlings during cycles of drought and recovery. New Phytologist. 205:1095-1105.Interpretive Summary: Air seeding was confirmed as the primary mechanism of drought-induced cavitation in coast redwood although a small number of tracheids initially became embolised via another mechanism. There was no evidence of embolism repair after drought.
                                Technical Abstract: The formation of emboli in xylem conduits can dramatically reduce hydraulic capacity and represents one of the principal mechanisms of drought induced mortality in woody plants. Some angiosperm species possess a mechanism to rapidly repair embolism by dissolving gas back into solution. However, it is unknown if conifer species possess a similar mechanism.  Using synchrotron based micro computed tomography (microCT), we examined embolism in the xylem of coast redwood (Sequoia sempervirens) seedlings that were subjected to cycles of drought and rewatering. Embolism formation was observed occurring by three different mechanisms: as tracheids embolizing in wide interconnected bands, as isolated tracheids in seemingly random events, and as functional groups connected to photosynthetic organs. Embolism spread outward from tracheids adjacent to the pith to the outer regions of the stem. The transition zone between earlywood and latewood tracheids appeared to act as a point of resistance for embolism spread, with latewood tracheids cavitating before earlywood tracheids. Upon rewatering, stem water potential recovered to pre-drought stress levels within 24 hrs, however, no evidence of embolism repair was observed even after a further two weeks under well watered conditions. The results indicate intertracheid air seeding is the primary mechanism by which embolism spreads in the xylem of S. sempervirens, but also showed that a small number of tracheids initially become gas filled via another mechanism. The inability of S. sempervirens seedlings to reverse drought induced embolism after recovery of stem water potential is most likely related to the non-reversibility of tori sealing over the pit apertures after aspiration.


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