Abstract:

A coupled model of leaves transpiration rate (Tr) and stomatal conductance (Gs) was developed to simulate the dynamic variation of Tr in apple canopy. The model used the Penman-Monteith equation to compute the interactive effects between Tr and microclimatic factors. And Gs was caculated by the semi-mechanism model. The experiment was conducted in a ‘Fuji’ apple (Malus domestica Borkh. cv. ‘Fuji’) orchard. The parameters of the model were tested by the data observed in upper canopy from 2007 to 2008 during the growing seasons. The mathematical simulation indicated that Tr increased rapidly with increasing Ta and Ψl; but decreased with increasing air CO2 concentration. Tr consistently increased with the increase of PAR when PAR was below photosynthesis light saturation point. And only a slightly increase was found when PAR excess light saturation point. It was shown that Tr was driven mainly by stomatal conductance, the most influential factor, and vapor pressure deficit. And the influences of these factors were different and there were strong interactive effects of various microclimatic factors on Tr. During the course of 1 day, transpiration increased (decreased) as net radiation and stomatal conductance increased (decreased). Maximum transpiration rates of the upper canopy leaves were about 4 mmol/(m2?s) on clear days. Over 24 h, a unit leaves area lost 2.7 L of water in clear weather and about 1.6 L in cloudy weather. In conclusion, the response of Tr to microclimatic factors and leaf water potential (Ψl) could be simulated by the coupled model.