Comparison between grapevine tissue temperature and air temperature.

Abstract Tissue temperature rather than ambient air temperature determines the rate of the processes that affect plant growth and development at molecular and cellular scales. Therefore, the use of air temperature to represent the temperature at which these processes occur within a plant organ implies a critical, yet poorly tested, assumption for most eco-physiological studies. The goal of this study was to determine whether the temperature of the tissues of field-grown grapevines differs significantly from the air temperature measured at a standard weather station. Thermocouples and infrared thermometers were used to measure the temperature of xylem at different heights in the west and east sides of the trunk of the vines, compound buds, and leaf surface in a vineyard between 2015 and 2017. The temperature of these tissues was compared with the air temperature measured at a standard weather station located at a distance of 410 m from the vineyard. Significant differences (p < 0.05) were determined between the temperature series. The significance and magnitude of the differences depended on the time of day and season of the year. In general, the tissue temperatures measured during the day were significantly higher than the air temperature recorded at the same time, and this difference was more than 2 °C in several cases. During the night, the tissue temperature was lower than the air temperature, but the difference was not greater than 2 °C. The higher thermal amplitude in the tissues due to these differences could explain some site- and time-specific patterns observed by viticulturists, such as the deacclimation or loss of cold hardiness during the day at higher than expected rates based on air temperature. [ABSTRACT FROM AUTHOR]