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Title:   Author  item
                                            Gleason, Seanitem
                                            WESTOBY, MARK - Macquarie Universityitem
                                            JANSEN, STEVEN - Ulm Universityitem
                                            CHOAT, BRENDAN - Western Sydney Universityitem
                                            HACKE, UWE - University Of Albertaitem
                                            PRATT, ROBERT - California State Universityitem
                                            BHASKAR, RADIKA - Haverford Collegeitem
                                            BRODRIBB, TIM - University Of Tasmaniaitem
                                            BUCCI, SANDRA - The National University Of The Pagagonia San Juan Boscoitem
                                            CAO, KUN-FANG - Guangxi Universityitem
                                            COCHARD, HERVE - Centre National De La Recherche Scientifiqueitem
                                            DELZON, SYLVAIN - University Of Bordeauxitem
                                            DOMEC, CHRISTOPHE - Duke Universityitem
                                            FAN, ZE-XIN - Chinese Academy Of Sciencesitem
                                            FIELD, TAYLOR - James Cook Universityitem
                                            JACOBSEN, ANNA - California State Universityitem
                                            JOHNSON, DAN - University Of Idahoitem
                                            LENS, FREDERIC - Leiden Universityitem
                                            MAHERALI, HAFIZ - University Of Guelphitem
                                            MARTINEZ-VILALTA, JORDI - Autonomous University Of Barcelonaitem
                                            MAYR, STEFAN - University Of Innsbruckitem
                                            MCCULLOH, KATHERINE - University Of Wisconsinitem
                                            MENCUCCIN, MAURIZIO - University Of Edinburghitem
                                            MITCHELL, PATRICK - Commonwealth Scientific And Industrial Research Organisation (CSIRO)item
                                            MORRIS, HUGH - Ulm Universityitem
                                            NARDINA, ANDREA - University Of Triesteitem
                                            PITTERMANN, JARMILA - University Of Californiaitem
                                            PLAVOCA, LENKA - University Of Albertaitem
                                            SCHREIBER, STEFAN - University Of Albertaitem
                                            SPERRY, JOHN - University Of Utahitem
                                            WRIGHT, IAN - Macquarie Universityitem
                                            ZANNE, AMY - George Washington University
  Submitted to: New Phytologist
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 8/13/2015
                                    Publication  Date: 1/8/2016
                                    Citation: Gleason, S.M., Westoby, M., Jansen, S., Choat, B., Hacke, U.G., Pratt, R.B., Bhaskar, R., Brodribb, T.J., Bucci, S.J., Cao, K., Cochard, H., Delzon, S., Domec, C., Fan, Z., Field, T.S., Jacobsen, A.L., Johnson, D.M., Lens, F., Maherali, H., Martinez-Vilalta, J., Mayr, S., Mcculloh, K.A., Mencuccin, M., Mitchell, P.J., Morris, H., Nardina, A., Pittermann, J., Plavoca, L., Schreiber, S.G., Sperry, J.S., Wright, I.J., Zanne, A.E. 2016. Weak tradeoff between xylem safety and xylem-specific hydraulic efficiency across the world’s woody plant species. New Phytologist. doi:10.1111/nph.13646.Interpretive Summary: •	The evolution of xylem (wood tissue) in plant species allowed for the transport of water under negative tension.  This means water could be “drawn up” through the xylem, driven by the energy of the sun.  However, drawing water through xylem using negative tension also exposes xylem to the risk of spontaneous bubble formation (gas embolism) and the subsequent spread of this gas between xylem conduits.  If emboli occur in sufficient quantity, water transport to the leaves is slowed down and, in severe cases, stopped, thus also arresting plant growth.  A well-known hypothesis proposes that the safety of xylem (its ability to resist embolism formation and spread) should trade off against xylem efficiency (its capacity to transport water).  
•	We tested this safety-efficiency hypothesis in branch xylem across 335 angiosperm (flowering seed plants) and 89 gymnosperm species (non-flowering seed plants).  
•	Although associations between safety and efficiency were weak, no species had high both efficiency and high safety, supporting the idea for a safety-efficiency tradeoff.  However, many species had low efficiency and low safety.  Species with low efficiency and low safety were weakly associated with higher wood density, lower leaf-area to sapwood-area, and shorter stature.  
•	There appears to be no persuasive explanation for the considerable number of species with both low efficiency and low safety.  These species represent a real challenge for understanding the evolution of xylem.
                                Technical Abstract: •	The evolution of lignified xylem allowed for the efficient transport of water under tension, but also exposed the vascular network to the risk of gas emboli and the spread of gas between xylem conduits, thus impeding sap transport to the leaves.  A well-known hypothesis proposes that the safety of xylem (its ability to resist embolism formation and spread) should trade off against xylem efficiency (its capacity to transport water).  
•	We tested this safety-efficiency hypothesis in branch xylem across 335 angiosperm and 89 gymnosperm species.  Safety was considered at three levels: the xylem water potentials where 12, 50, and 88% of maximal conductivity are lost.  
•	Although correlations between safety and efficiency were weak (r2 < 0.086), no species had high efficiency and high safety, supporting the idea for a safety-efficiency tradeoff.  However, many species had low efficiency and low safety.  Species with low efficiency and low safety were weakly associated (r2 < 0.02 in most cases) with higher wood density, lower leaf-area to sapwood-area, and shorter stature.  
•	There appears to be no persuasive explanation for the considerable number of species with both low efficiency and low safety.  These species represent a real challenge for understanding the evolution of xylem.


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