Understanding how vines deal with heat and water deficit

Transcription

1 Understanding how vines deal with heat and water deficit Everard Edwards CSIRO AGRICULTURE & FOOD

2 How hot is too hot? Cell death will occur in any vine tissue beyond a threshold (lethal) temperature cell membrane can melt, proteins can become denatured. Threshold temperature for a grapevine leaf is probably >5 C exact temperature will depend on variety & level of heat acclimation. We don t grow vines in regions with air temperatures this high, so why is heat a problem?

3 The problem with heat Water? Exposed tissues (e.g. leaves) are absorbing energy from sunlight. Energy that cannot be utilised (i.e. photosynthesis) will heat the leaf. Vine productivity can be affected photosynthetic apparatus may be permanently damaged 1 C below lethal temperature, any leaf death reduces future carbon accumulation. But, does the leaf reach >5 C? usually thought hydraulic failure precedes lethal temperatures.

4 Plants need water Water is required for: cell function, photosynthesis, transport of photosynthate & nutrients. Water moves from root to shoot and is lost from the leaves. The plant is part of the soilto-air continuum. Water deficit interferes with these processes.

5 Stomata and transpiration Movement of water from the vine to the air is termed transpiration and occurs through the stomata. The underside of a vine leaf is covered in small pores: stomata. H 2 O

6 Stomatal conductance Water loss and carbon uptake are directly linked! The stomata are also the site where CO 2 enters the leaf (for photosynthesis). Stomatal opening is under tight control by the plant. The extent of stomatal opening is termed conductance. CO 2 H 2 O

7 Vapour pressure deficit Vine water use is determined by: stomatal conductance, canopy size, vapour pressure deficit. Vapour pressure deficit (VPD): VPD = amount of water in saturated air (1 %RH) - actual amount of water in the air The amount of water required to saturate air increases with temperature. Therefore, VPD typically increases with temperature. VPD (kpa) 7 Relative humidity of 5% at 25 C Air Temperature ( C) higher %RH less transpiration lower %RH more transpiration

8 Effect of VPD and conductance on transpiration Transpiration (arbitrary units) mmol m -2 s -1 3 mmol m -2 s mmol m -2 s mmol m -2 s -1 Water loss increases even with a 7% reduction in conductance VPD (kpa) Increasing VPD results in greater water loss from the leaf for a given value of conductance. Effect of high temperature on water use may be greater than the effect of reduced conductance.

9 Conductance responds to VPD: varietal differences Transpiration (arbitrary units) mmol m -2 s -1 3 mmol m -2 s mmol m -2 s mmol m -2 s -1 Water loss increases even with a 7% reduction in conductance VPD (kpa) Conductance (mmol m -2 s -1 ) Transpiration (mol m -2 s -1 ) Low VPD High VPD Grenache Chardonnay Shiraz Soar et al. (26) AJGWR

10 Drivers of vine water use an example 8 Vine water use is a function of: vapour pressure deficit (VPD)*, canopy size/structure, stomatal opening. Daily vine water use (L d -1 ) Large canopy Moderate canopy Small canopy Small canopy + water stress Daily ET o (mm) *modified by boundary layer/wind. Cabernet Sauvignon, Sunraysia (Edwards et al.)

11 Effect of water deficit on conductance Stomatal conductance (mmol m -2 s -1 ) ML ha Sustained deficit irrigation (reduced from fruit-set to leaf fall). Impact of reduced soil water availability present throughout season. Low conductance reduces vine water use, but also reduces photosynthesis. Pre-harvest Post-harvest Loveys et al. unpublished. Cabernet Sauvignon vines in the Riverland.

12 Transpiration affects leaf temperature Leaf temperature C Air temperature Seconds Slide courtesy of Brian Loveys

13 Transpiration affects leaf temperature Leaf temperature C Air temperature Seconds Slide courtesy of Brian Loveys

14 Transpiration affects leaf temperature Leaf temperature C Air temperature Seconds Slide courtesy of Brian Loveys

15 What is a heatwave? High-temperature event and heatwave are relative terms: high temperature stress in one region may be normal growing temperature in another, the same temperature at different times of the season may have a different impact. However: absolute temperature is important, duration is important, humidity is important. High VPD will stress the vine at any temperature. Low VPD may reduce the potential effects of high temperature.

16 Impacts of heat on well-watered vines Under well watered conditions, even air temperatures of 45 C may generate only mild heat stress symptoms in the canopy. Supported by data from the field (under both natural and artificial heatwaves) and from the glasshouse (using both mature vines in large pots and young vines in small pots) Conductance (mol m -2 s -1 ) C 43 C Transpiration (mmol m -2 s -1 ) C 43 C Photosynthesis (μ mol m -2 s -1 ) C 43 C Edwards et al. (213) unpublished. Artificial heatwave with Cabernet Sauvignon vines, Murray Valley.

17 Heatwaves and water deficit But under water deficit conditions vines cannot cope with heatwaves. Well-watered 29/1 season, 13 days >4 C, Murray Valley. Water-stressed Edwards et al. (21) Cabernet Sauvignon vines from the same row.

18 Water deficit and high temperature in combination In general water deficit (drought) exacerbates heat stress due to: greater stomatal closure, resulting in higher leaf temperatures, reduced vine water status, increasing risk of hydraulic failure and wilting. High temperature usually results in high VPD (low %RH), increasing water loss, even with low stomatal conductance. Wilting of canopy increases fruit exposure and temperature.

19 Heatwaves and water deficit conductance & transpiration Difficult to study in the field, CSIRO has run a number of glasshouse experiments Transpiration (mmol m -2 s -1 ) Conductance (mmol m -2 s -1 ) Heat Heat Heat Heat Edwards et al. (211), AJGWR.

20 Heatwaves and water deficit leaf temperature Difficult to study in the field, CSIRO has run a number of glasshouse experiments Transpiration (mmol m -2 s -1 ) Leaf Temperature ( C) Heat Heat 2 Heat Heat Edwards et al. (211), AJGWR.

21 Heatwaves and water deficit water status Difficult to study in the field, CSIRO has run a number of glasshouse experiments.. Pre-heat stress. During artificial heatwave Water status: Ψ stem (kpa) Water status: Ψ stem (kpa) Heat Heat Tesfamicael, Edwards, Rodriguez (217), unpublished.

22 Heatwaves and water deficit - damage The vine s ability to cope with heatwaves is proportional to the water stress present No damage 2 12 Number of Vines 8 4 <25% leaf loss 25-5% leaf loss 5-75% leaf loss Number of Vines % leaf loss 4 Heat Heat 1% 25% 5% Treatment Leaf loss in vines heated to >45 C. Edwards et al. (211), AJGWR.

23 Summary of biology Damage to tissues by heat stress likely due to lack of water supply rather than heat per se. Therefore, water status of canopy is key to heat stress tolerance in short-term. VPD (%RH) is the primary driver of day-to-day changes in vine water use. Maintaining open stomata/high transpiration (cooling) during heatwave can require four-fold increase in water uptake. Protect canopy to protect fruit. Longer-term solutions may also include considering solar radiation load.

24 Acknowledgements Past and current staff and students of grapevine physiology team at CSIRO. Work described funded by Wine Australia & CSIRO. CSIRO Agriculture and Food Everard Edwards Research Team Leader t e Everard.edwards@csiro.au w AGRICULTURE AND FOOD