EFFECTS OF TEMPERATURE AND POTASSIUM CHLORATE ON LEAF GAS EXCHANGE AND FLOWERING IN LONGAN

Abstract

The effects of low temperature and potassium chlorate (KClO 3 ) on leaf gas exchange and flowering of sixty four grafted longan trees cv. 'Daw' (Dimocarpus longan Lour.) were investigated. The longan trees were kept in two growth chambers under low temperature (17/12°C day/night), high temperature (30/25°C day/night) half of the trees in each room were treated with KClO 3 , respectively. The results showed that flower emergence in longan occurred 37 days following low temperature and high temperature exposure with KClO 3 treatment, while low temperature with KClO 3 delayed flowering and high temperature exposure completely inhibited flowering. Efficiency of photosystem II (Fv/Fm) as well as leaf net CO 2 assimilation rate decreased under low temperature and KClO 3 treatments, when compared to the high temperature treatments. Transpiration rate and stomatal conductance were both reduced in low temperature no matter whether KClO 3 was applied. After 28 days, when temperature in low temperature treatments were increased, net CO 2 assimilation rate, transpiration rate and stomatal conductance also increased to similar values found in high temperature treatments. Both temperature and KClO 3 treatments did not affect the chlorophyll content of longan leaves.