High Temperature Effects on Leaf Resistance, Leaf Water Potential, and Photosynthesis of Non-bearing Prune Trees1

Abstract

The effects of ambient temperatures between 15° and 43°C were determined on net photosynthesis of ‘French’ prune (Prunus domestica L. cv. Agen) trees maintained under a non-limiting soil water supply. The temperature optimum for photosynthesis was about 30° and net CO2 assimilation decreased rapidly above 35° even when water vapor pressure differences (VPD) were only 5 to 10 mb. Leaf resistance (r1) remained very low (2 to 3 sec cm-1) although leaf temperature reached 47° and the leaf water potential (ψ) decreased to -25 bars. Thus, non-stomatal photosynthetic inhibition was responsible for the 80% decline in net CO2 assimilation. Canopy wetting prevented the decline in net CO2 assimilation by reducing leaf temperature 8° (vs. control) and maintaining the ψ 14 bars higher than the non-misted control.

Stomatal Response of Three Grapevine Cultivars (Vitis viniferaL.) to High Temperature

“…In addition, for Experiment 3, D was calculated (Table 3). In all experiments, Cs increased with increasing PAR as well as with T. However in most plants, stomata opened in response to T only up to a certain temperature threshold (which varied with each species) after which they closed (2,7,10,23). At extremely high T (e.g., 40°C) Cs may decrease due directly to changes in leaf water status resulting from high transpiration rates, to increased intercellular CO2 due to high temperature inhibition of photosynthesis, or to changes in endogenous abscisic acid levels resulting from plant water stress.…”

“…Correlation analysis of Cs versus RH and T over time showed no significant relationship existed for the three experiments, except for significant and positive Cs response of heat-stressed Cardinal vines to T. The opening of stomates at high temperature has been observed for many other plant species (2,7,21,23). The increased stomatal openings at high temperature are believed to be associated with enhanced evaporative cooling of leaves, reducing the likelihood of thermal damage to tissue (5).…”

“…Similar conclusions were obtained by Schulze et al (22,24,25) for apricots under desert conditions, adding that under these conditions, stomata respond to temperature and air humidity irrespective of a wide range of total water potential and internal CO2 concentrations. However, Even-Chen et al (2) reported that with prune trees stomatal conductance increased from 0.15 to 1.00 cm sec -1 when temperature increased from 25 ° to 40°C, despite a much larger vapor pressure deficit.…”

“…Studies on stomatal response to temperature have often yielded contradictory results; Heath and Orchard (9) and Heath and Meidner (8) observed stomatal closure with increasing temperature, while Hofstra and Hesketh (10), Drake et al (1), Schulze et al (23), Hall et al (7), Rogers et al (21), and Even-Chen et al (2) found that stomata opened with increasing temperature. Also, maximum stomatal opening at an intermediate temperature has been reported (10,18,19).…”