Ben-Min Chang and Markus Keller*
*Washington State University, 24106 N. Burrn Rd., Prosser, WA 99350 (mkeller@wsu.edu)

Because of the rising atmospheric carbon dioxide concentration, the frequency and scale of extreme weather events is increasing. Grapevines can acclimate to a stable temperature trend and optimize their physiological performance at that condition. The magnitude of temperature change determines how well the vines adapt to the new condition. However, a sudden, large change in temperature can compromise productivity and fruit quality. We developed a mist-type evaporative cooling system to control canopy temperature without compromising deficit irrigation and stimulating vegetative growth. In the current configuration, the threshold to activate misting is arbitrarily and inflexibly set at 35°C. To optimize operation of the canopy cooling system, knowledge about how grapevines acclimate to temperature change is essential. We grew potted Cabernet Sauvignon vines in growth chambers at high (32°C/15°C) and low (27°C/10°C) maximum/minimum temperature regimes for 10 days, simulating hot and cool growing seasons in eastern Washington. Then the vines were exposed to a spectrum of maximum temperatures varying from 40°C to 25°C, maintaining a 17°C difference between daily maximum and minimum temperature. Gas exchange rate was monitored at noon and late afternoon. The results suggested that grapevines are more vulnerable to a sudden temperature spike (heat wave) in a cool season than in a warm season. The photosynthesis rate and stomatal conductance at noon were depressed when the cool-acclimated vines were suddenly exposed to higher temperature. In the late afternoon, vines from both acclimation regimes showed gas exchange depression when the vines were exposed to temperatures above the acclimation conditions. Overall, the temperature acclimation experiment suggested the temperature which causes heat stress is flexible and depends on previous environmental conditions. Hence, using a dynamic activation threshold temperature for the cooling system might maintain vine gas exchange capacity better than a fixed threshold temperature.

Funding Support: Northwest Center for Small Fruits Research; USDA Specialty Crop Block Grant Program; Washington State Grape and Wine Research Program