Author
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Glenn, David |
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Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/23/2009 Publication Date: 6/16/2009 Citation: Glenn, D.M. 2009. Particle film mechanisms of action that reduce the effect of environmental stress in 'Empire' apple. Journal of the American Society for Horticultural Science. 134(3):314-321. Interpretive Summary: Heat stress is a limiting factor of plant productivity throughout the world, and kaolin-based particle films (PF) have demonstrated that the reflective nature of the resulting plant surface can increase plant productivity primarily by reducing temperature in fruit, leaf, and canopy, but the underlying plant physiological responses are not clear. Apple trees received either no treatment or season-long applications of a PF treatment, and each treatment received no supplemental irrigation of full replacement of evapotranspiration from 1998 to 2007. The study demonstrated that the combination of PF and adequate water could maintain maximum photosynthesis rates at full sun levels during the midday period, minimize the midday depression of photosynthesis that is commonly observed, and reduces the daily carbon accumulation. The increased carbon accumulation during the midday period was likely diverted to the fruit since the PF treatments increased fruit weight in 8 of 10 years. The use of PF may be an effective substitute for evaporative cooling not only to reduce fruit solar injury, but to improve apple quality through increase fruit weight in hot and dry climates. Technical Abstract: Heat stress is a limiting factor of plant productivity throughout the world, and kaolin-based particle films (PF) have demonstrated that the reflective nature of the resulting plant surface can increase plant productivity primarily by reducing temperature in fruit, leaf, and canopy. The purpose of the present study was to evaluate the environmental mechanisms and related physiological responses of 'Empire' apple (Malus domestica) gas exchange at the canopy level to PF treatments in order to identify those parameters key to plant response and increased plant productivity. Trees received either no treatment or season-long applications of a PF treatment, and each treatment either received no supplemental irrigation of full replacement of evapotranspiration. Studies were begun in 1998 and continued to 2007. Fruit number and fruit weight were measured in all years. Whole canopy carbon dioxide assimilation rates (A) were measured in apple for a four-year period to determine the relationship with incoming light and vapor pressure deficit (VPD) levels. The photosynthetic response to the irrigation and PF treatments varied between years due to environmental variation, and the VPD was more limiting than photosynthetically active radiation. There was a unique treatment response for PAR levels > 1600 µmol·m-2·s-1 in which the combination of PF and irrigation maintained midday A at maximum levels compared to other treatments even though A was reduced by increasing VPD. This response indicated that while VPD limited A, the combination of PF and adequate water could maintain maximum A rates at full sun levels during the midday period and minimize the midday depression of A that is commonly observed and reduces the daily carbon accumulation. The increased carbon accumulation during the midday period was likely partitioned to the fruit. Increased fruit weight with the PF treatment, compared to the control, was positively correlated with the growing season air temperature and VPD indicating that as the environment becomes hotter and/or drier, the magnitude of the PF response increased due to the reduced leaf and fruit temperature, and the subsequent physiological effect. The PF treatments reduced radiation and heat load on exposed leaves enabling them to better regulate leaf temperature and improved the light distribution inside the canopy resulting in increased carbon gain at the whole-plant scale. The use of PF may be an effective substitute for evaporative cooling not only to reduce solar injury, but to improve apple quality through increased fruit weight. The results suggest that benefits of PF treatments would occur in agroecosystems with large VPD’s and high temperatures, and that the inclusion of irrigation would further enhance the benefits at high PAR levels. |
