High-throughput phenotyping technologies allow accurate selection of stay-green

changes during shrinkage, aquaporin activity and/or changes in the vapor phase transport. The application of models calibrated with anatomy will be an essential approach to determining the drivers of K ox decline. Finally, speculation that K ox decline may protect the xylem in the leaf and throughout the rest of the plant from tensions that induce embolism needs to be validated using models and measurements of whole-plant transport. If K ox decline turns out to be the major driver of K leaf decline, this will shift our understanding of water transport in the whole plant, and thus in the entire soil–plant–atmosphere continuum. No longer will water flow through soil or dead xylem cells be considered the major control points – rather, the living tissues outside the xylem, including the stomata, leaf vein parenchyma and leaf mesophyll, may take a central position. The light and turgor responses of these cells within leaves would then be recognized as influencing water transport and stomatal sensitivity, drought tolerance and productivity at plant and landscape scale. Outside-xylem hydraulic conductance will need to be explicitly incorporated into new models of plant water use, ecohydrology, landscape and global fluxes, and climate. The dissection of leaf hydraulic pathways would thus shift our understanding of how living plant cells and tissues influence the biosphere. References Blackman CJ, Brodribb TJ, Jordan GJ. 2010. Leaf hydraulic vulnerability is related to conduit dimensions and drought resistance across a diverse range of woody angiosperms. The contributions of apoplastic, symplastic and gas phase pathways for water transport outside the bundle sheath in leaves. A. 2016. Role of leaf hydraulic conductance in the regulation of stomatal conductance in almond and olive in response to water stress. Dynamics of leaf hydraulic conductance with water status: quantification and analysis of species differences under steady-state. Journal of Experimental Botany 63, 643–658. Scoffoni C, Sack L. 2015. Are leaves " freewheeling " ? Testing for a Wheeler-type effect in leaf xylem hydraulic decline. contribution of vascular and extra-vascular water pathways to drought-induced decline of leaf hydraulic conductance. Improved genotypic performance in water-limited environments relies on traits, like 'stay-green', that are robust and repeatable, correlate well across a broader range of target environments and are genetically more tracta-ble than assessment of yield per se. Christopher et al. (see pages 5159–5172) used multi-temporal, Normalised permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.