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.
Tasmanian Institute of Agricultural Research, University of Tasmania, Private Bag 98, Tasmania, Australia.
Meisha-Marika
MM
Holloway-Phillips
Timothy J
TJ
Brodribb
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