Surface temperature of plant tissues. Which method of air temperature measurement fits best?

Abstract

Climate change is contributing to an increased risk of flower damage by late spring frosts. Monitoring flower temperature is critical for the timely start of frost protection systems. However, there are many weak points that complicate the use of this method. The aims of this study were to: i) find the method of air temperature measurement with the best relationship to the surface temperature of plant tissues and ii) quantify the differences between plant tissues surface temperature and ambient temperature during different weather situations. The surface temperature of plant tissues (budding leaves of grapevine, apricot flower, and unripe pear fruit), air temperature and humidity in the radiation shield, wet bulb temperature and air temperature with an unsheltered thermometer were measured at ten-minute intervals in the spring months. The average temperatures obtained by the individual methods as well as the lowest temperatures were determined from each measurement. Differences between air temperatures and plant surface temperatures, including variation ranges, were also determined. An unsheltered thermometer, in which the energy balance corresponds approximately to that of the evaluated plant surfaces, provided the best relationship with plant tissue temperature. The air temperature measured by the standard method (in a Stevenson screen or in the radiation shield) was almost always higher than the temperature of the plant tissue during periods of negative energy balance. The difference between the minimum temperatures was approximately 0.5 °C. Temperatures more than 1.5 °C higher than the actual temperature of plant tissues were measured in extreme cases.