Minimum hydraulic safety leads to maximum water-use efficiency in a forage grass.
Understanding how water-use regulation relates to biomass accumulation is imperative for improving crop production in water-limited environments. Here, we examine how the vulnerability of xylem to water stress-induced cavitation and the coordination between water transport capacity and assimilation (A) influences diurnal water-use efficiency (WUE) and dry-matter production in Lolium perenne L. - a commercial forage grass. Plants were exposed to a range of water stresses, causing up to 90% leaf death, by withholding water and then rewatering to observe the recovery process. Leaf hydraulic conductance (K(leaf) ) declined to 50% of maximum at a leaf water potential (ψ(leaf) ) of -1 MPa, whereas complete stomatal closure occurred well after this point, at -2.35 MPa, providing no protection against hydraulic dysfunction. Instantaneous A remained maximal until >70% of hydraulic conductivity had been lost. Post-stress rewatering showed that 95% loss of K(leaf) could be incurred before the recovery of gas exchange exceeded 1 d, with a rapid transition to leaf death after this point. Plants exposed to sustained soil water deficits through restricted nightly watering regimes did not suffer cumulative losses in K(leaf) ; instead, ψ(leaf) and gas exchange recovered diurnally. The effect was improved WUE during the day and optimal ψ(leaf) during the night for the maintenance of growth.
Holloway-Phillips
Meisha-Marika
MM
Tasmanian Institute of Agricultural Research, University of Tasmania, Private Bag 98, Tasmania, Australia.
Brodribb
Timothy J
TJ
D002940:Circadian Rhythm; D003624:Darkness; D003681:Dehydration; D057446:Hydrodynamics; D008027:Light; D008129:Lolium / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D018515:Plant Leaves / Q000502:physiology; D054046:Plant Stomata / Q000502:physiology; D018526:Plant Transpiration / Q000502:physiology*; D011897:Random Allocation; D012987:Soil; D013997:Time Factors; D014867:Water / Q000378:metabolism*; D052584:Xylem / Q000502:physiology
D012987:Soil; D014867:Water