Observations of night-time water use in kiwifruit vines and apple trees

Abstract

Transpiration rates of two 7-year-old kiwifruit vines ( Actinidia deliciosa) and a 10-year-old apple tree ( Malus sylvestris × Red delicious) were measured for 15 days in summer using the heat-pulse technique. Environmental data were collected at the same time, every half-hour. Significant transpiration rates were observed at night, in both kiwifruit and apple, whenever the saturation deficit remained elevated. Night-time water use in kiwifruit plants ranged from 1.4 to 19.2 l, for saturation deficits of between 0.44 and 3.1 g kg −1. Nocturnal transpiration of the apple tree ranged from 0.3 to 5.3 l for saturation deficits between 0.2 and 3.3 g kg −1. Mean night-time water use for kiwifruit and apple was 19% ( n = 15 nights) and 6% ( n = 15), respectively of the total daily transpiration. Nocturnal transpiration increased linearly with mean saturation deficit and saturation deficit increased with mean wind speed. Nocturnal transpiration was therefore greater on windy nights. The directly measured nocturnal transpiration rates in kiwifruit were compared with rates of water use calculated using the Penman-Monteith combination equation with stomatal resistance data obtained by porometry on one night. There was satisfactory agreement between the two results.