Monitoring sap flow on grapevines during extreme heatwave events has demonstrated that vines can tolerate extreme conditions when soil moisture levels were high. These results were found via the grapevine and heatwave monitoring project in the Riverina region of New South Wales (NSW), Australia.
Heatwaves are “three or more days of high maximum and minimum temperatures that are unusual for that location” (Bureau of Meteorology, Australia). With increasing greenhouse gas emissions, heatwaves are also increasing in frequency and duration. The response of horticultural and agricultural crops to heatwaves is critical for plant health, growth, yield and product quality.
The results from the 2018-2019 grapevine growing season indicated that, when soil moisture was maintained at a high level through irrigation, grapevines did not decrease sap flow, or show any adverse affects, to extreme temperature and heatwave conditions.
These results suggest that important economic crops can tolerate extreme temperature if they are supported by irrigation. Where irrigation is unavailable, or the cost of water is prohibitive, then it may be difficult for growers to manage crops through heatwave events.
the grapevine heatwave project
In association the Riverina Winegrape Growers, Wine Australia, the NSW Department of Primary Industries and Edaphic Scientific, phytomonitoring stations were installed in November 2017 in the Riverina grape growing region of New South Wales, Australia, to monitor grapevine response to heatwave events.
Results from the 2017-2018 growing season can be found here. This article updates the project with new results from the 2018-2019 growing season.
the phytomonitoring stations
The phytomonitoring stations consisted of Implexx Sap Flow Sensors, Stem and Trunk Dendrometers, canopy microclimate temperature and relative humidity sensors, and soil water content and soil temperature sensors. Sensors were installed on Shiraz, Merlot, Cabernet Sauvignon, and Chardonnay grapevine varieties.
the 2018-2019 growing season
Extreme temperature conditions were frequent during the 2018-2019 growing season. For example, during January 2019, the daily maximum temperature in the Riverina region exceeded 40 ˚C on 17 days. Despite the extreme temperature, there was no discernible effect on grapevine sap flow. That is, grapevine sap flow was positively correlated with temperature throughout the entire growing season.
Sap flow is often used as a measure of plant health where a decrease in sap flow indicates a plant undergoing stress. Although sap flow is mainly related to the water relations of plants, there is also a correlation with stomatal conductance, carbon uptake and photosynthesis. During the heatwave, it is possible the grapevines maintained a high level of sap flow as a canopy cooling effect and there may have been down-regulation in photosynthesis. That is, transpiration (sap flow) was maintained at a high rate, because grapevines had access to ample soil moisture, but may, or may not, have altered their photosynthetic rate. Unfortunately, these additional parameters were not measured during the heatwaves of the 2018-2019 growing season so we can only speculate. In future seasons, it is intended that additional parameters, particularly related to vine growth, berry yield and quality, will be measured.
For detailed explanation of the 2018-2019 growing season results, and implications for irrigation management strategies, as well as plant physiology generally, download the following PDF article:
- The 2017-2018 Riverina Sap Flow Results
- Sap flow sensors
- Soil moisture sensors
- Phytomonitoring systems