Transpiration of apple trees as related to different meteorological, plant and soil factors

Abstract

SummaryThe effects of different soil water regimes were investigated on the mean transpiration rate (TRm) of cv Granny Smith apple trees under a given set of meteorological factors. Instantaneous transpiration rates of sunlit and shaded plant parts were determined at different times of the day and at regular time intervals during the growing season. Transpiration losses of the trees were found to vary from 15 to 71 mg m-2 s_1 during the 1977/78 season and from 22 to 92 mg m-2 s1 during the 1978/79 season. The ratio of shaded to sunlit TRm was 0.43 ± 0.07. Transpiration rates under a 25% total available soil water (TAW) level were 45 ± 6% of those under an 85% TAW level. Leaf temperature (T1) was 4.5°C above ambient. Stomatal resistances (r) of sunlit leaves under a 25% TAW level were higher than for an 85% TAW level, but the differences were much smaller than for shaded leaves. Factor analysis clustered all variables into four factors. These factors indicate that wind velocity (v), T1, r and soil water pressure (SWP) are the most important variables that govern TRm rate. Multiple regression analysis showed that v, T., r and SWP explain 83% of the variation in TRm rate. Transpiration was negatively correlated with ν and r, and positively correlated with T1 and SWP (r = 0.91).