Responses of apple leaf stomata: a model for single leaves and a whole tree

Abstract

An empirical model of stomatal response to environmental factors was developed from measurements of stomatal conductance (gs) made in a leaf chamber under controlled conditions. Results presented in a companion paper (Warrit, Landsberg & Thorpe, 1980) indicated that the model could be written in terms of only two factors, photon flux density (^p) and leaf to air vapour pressure gradient (D). The response of Qp was hyperbolic and that to D linear; combining these the equation ofthe model iswhere gr is a reference conductance, a is the slope ofthe response to D and j9 indicates the sensitivity of gs response to Qp. Values of a were 0.20 and 0.30 kPa~' in June and August; the corresponding values of P were 59 and 79 ^umol m~-^ s"'.The model was tested against mean values of gs obtained with a porometer in the field, using environmental measurements as inputs. Correspondence between measured and calculated values was good. Transpiration rates were calculated from the PenmanMonteith equation, with stomatal resistance values calculated from the model, and compared with gravimetric measurements of tree water use. It was shown that transpiration could be calculated with acceptable accuracy. The effects of variations in stomatal resistance on transpiration rates under a range of conditions were explored using the model and the Penman-Monteith equation.

Environmental controls on stomatal conductance in a shrub of the humid tropics

“…This suite of responses describes a pattern in which stomata function primarily to regulate water loss, independent of photosynthetic rates. This pattern contrasts sharply with temperate patterns of balanced stomatal responses to multiple environmental factors (6)(7)(8) and with data from seasonal tropical plants indicating strong stomatal responses to light intensity (9).…”

Leaf and Simulated Whole‐Canopy Photosynthesis in Two Co‐Occurring Tree Species

“…where I is the incident PPFD, D. W is the leaf-air water vapor concentration gradient and a-d are empirically determined constants (Hollinger 1984). This is similar to the formulation used by Jarvis (1976), Thorpe et al (1980), and others.…”

Responses of apple leaf stomata to environmental factors

“…The leaf chamber measurements were started in the morning and continued through the day, environmental conditions being altered after steady state stomatal responses were observed, without regard to the time of day. The stomatal conductance values measured with the porometer certainly showed diurnal trends, but these could, in large part, be explained by analysis in terms of environmental conditions (see Thorpe et al 1979). Endogenous rhythms may have been swamped by the effects of environmental factors; if it were possible to determine the extent to which these causes of variation in stomatal conductance interact this may help to reduce the unexplained variability in results such as those presented here.…”