Changes in Temperature and Gas Exchange in Leaf of Pistachio (Pistacia vera L.) Seedlings in Response to Kaolin Application

In order to evaluate the effect of kaolin on leaf gas exchangein seedlings of pistachio (Pistacia vera L.), an experiment was conducted as split plot based on a completely randomized design with five replications in open field condition during year of 2013. Kaolin concentration at four levels (0, 5, 10 and 15%) and spraying time at three levels (once, two and three times) in 3×4 factorial as main factor and five sampling time as sub-factors were considered. Results of the experiment indicated that 5, 10 and 15% concentrations of Kaolin reduced leaf temperature by 1.1, 2 and 2.2°C compared to the control. Simple effect of spraying time on photosynthesis, stomatal conductance and transpiration was significant, whereas these traits significantly decreased when spraying was more than two times. Maximum photosynthesis, transpiration, stomatal conductance and intracellular CO2 were recorded in 5% Kaolin. Treatments of control and 15% Kaolin recorded maximum and minimum value in quantum yield with 0.89 and 0.88, respectively. Generally, 5% Kaolin concentration in one and two spraying time increased leaf gas exchange compared to the control due to the reduction in negative effects of high temperature. Nevertheless, high kaolin concentrations (10% and 15%) despite further lowering leaf temperature, decreased the photosynthesis of pistachio seedlings significantly due to increasing light reflection as a result the thick layer of kaolin on leaf and disruption of stomatal activity.