THE UWA INSTITUTE OF AGRICULTURE Postgraduate Showcase 2015 The role of transpiration in ameliorating leaf temperature in wheat in relation to changing environmental conditions Chandima Ranawana School of Plant Biology and UWA Institute of Agriculture
Acknowledgements Supervisors Hackett Prof. Kadambot Siddique Dr. Helen Bramley Adjunct Prof. Jairo Palta Funding Endeavour Postgraduate Research Awards School of Plant Biology The UWA Institute of Agriculture Inputs Mr. Bruce Piper, Bindi Bindi (soil) Dr. Greg Rebetzke, Dr. Dan Mullan (InterGrain), Australian Winter Cereal Collection (AWCC) and AGT
Global temperature by 2050 -------- Increases by 1-3 C Plants? Wheat - highly sensitive to heat stress physiological and biochemical changes Yield reductions Adaptation strategies???
Relative humidity Air temperature Vapour Pressure Deficit (VPD) Transpiration Open Closed Leaf temperature Stomata Efficiency of vascular system Soil water availability
Above-ground environment Plant morphological characteristics Transpiration and leaf temperature regulation Plant physiological characteristics Below-ground environment Role of transpiration? Mechanisms?
Greater water use vs biomass retention Morpho-physiologically diverse set of 20 wheat genotypes Assessed under Ambient temperature Well-watered High temperature (8-9 C higher)
Daily rate of transpiration under ambient and high temperature Daily rate of transpiration (g plant -1 day -1 ) Sonora 64 Wyalkatchem Excalibur Yecora 70 Ciano 67 Einkorn Janz Glennson 81 Downey Magenta Emu Rock LongReach-Envoy Gladius Hartog Kukri Mace Espada Glossy-huguenot Drysdale RAC
Greater water use increases shoot dry weight? Shoot dry weight (g plant -1 ) Ambient temperature (r = 0.97; P < 0.0001) High temperature (r = 0.98; P < 0.0001) Total water use (L plant -1 ) Biomass retention under high temperature Greater water use increased biomass retention Effect of leaf cooling on biomass retention?
Transpiration response to vapour pressure deficit Excalibur(slope3.0)Downey(slope1.6)Rate of transpiration (mmol H2O m-2 s-1) 1.0 < Transpiration < 3.1 Slope Transpiration response = slope Genotypic differences Vapour pressure deficit (kpa)
Excalibur(slope=0.6)Downey(slope=0.8)Air temperature ( C) 0.5 < Leaf temperature < 1.0 slope Leaf temperature response to air temperature Leaf temperature ( C) Leaf temperature response = slope Genotypic differences
Transpiration response vs leaf temperature responsejanzglennson81magentaespadakukrileaf temperature vs air temperature slope ( C C -1 ) Rate of transpiration vs VPD slope (mmol H 2 O m -2 s -1 kpa -1 ) Leaf waxiness
Contrasting responses of transpiration to vapour pressure deficit: Mechanisms? Eight genotypes (Contrasting responses) Growth chamber controlled conditions 6 Vapour pressure deficit levels (0.8 to 4.5 kpa) Well-watered Water-stressed
Transpiration response to vapour pressure deficit Two contrasting responses Rate of transpiration (mg H 2 O m -2 s -1 ) (B) Segmented linear (A) Simple linear Break point Vapour pressure deficit (kpa) (A) Simple linear Well-watered 2 out of the 8 genotypes (Gladius and Mace) Water-stressed Simple linear, but slower response (B) Segmented linear Well-watered 6 out of the 8 genotypes (Excalibur, Longreach-Envoy, Drysdale, Espada, Glennson 81 and Sonora 64) Water-stressed Changed to simple linear except in 2 (Espada and Drysdale)
ExcaliRate of transpiration (mg H 2 O m -2 s -1 ) GladiusWell-watered Well-watered Water-stressed Water-stressed buvapour pressure deficit (kpa) rwell-watered Break point 2.1 kpa (Excalibur) to 3.4 kpa (Glennson 81 and Sonora 64) Rate of increase with vapour pressure deficit (slope) segmented > linear Water-stressed Rate of transpiration and its response to vapour pressure deficit low
conductance (mol m -2 s -1 ) burstomatal ExcaliGladiusStomatal conductance response to VPD Well- watered Wellwatered Waterstressed Water-stressed Vapour pressure deficit (kpa) Well-watered Simple linear transpiration response group? Segmented linear transpiration response group? Water-stressed Stomatal conductance low and decreased with VPD except in 3 genotypes (non-responsive)
Conceptual Model (Differing coordination between stomata and root hydraulics) Rate of transpiration Transpiration A Stomatal conductance B Break point Vapour pressure deficit Root hydraulics (resistance) (A) Segmented linear Root resistance low? Excessive water escape Need a controlling mechanism Stomatal conductance decreased with vapour pressure deficit (B) Simple linear Root resistance high? Stomatal conductance constant with vapour pressure deficit
PDRoot hydraulicsvabbreakpointvpd Evaporative cooling Transpiration Leaf temperature Waxiness Pubescence Other mechanisms Reflectance Stomatal conductance Rate of transpiration (A(B))SeSigmmplenelteindealinearrLeaf temperature response vs transpiration response? Effect of transpiration and leaf cooling on biomass retention?
Practical implications? Development of wheat cultivars for target environments Rate of transpiration A Type A Segmented response For agricultural regions relying on in-season rainfall (Mediterranean-type environments). e.g. Western Australian grain belt B Type B simple linear Slower transpiration response. Conserve soil water for grain-filling. Break point Agricultural areas where yield depends on Vapour pressure deficit stored soil water from summer rainfall. e.g. North-eastern grain belt of Australia