Effect of Applied Abscisic Acid and Silicone on Water Relations and Photosynthesis of Woody Plants

Abstract

Fraxinusamericana and Pinusresinosa seedlings were treated with 7.5% silicone or 10−4 M ABA. Plants were watered on the day following treatment and then subjected to a soil drying cycle. At frequent intervals after the compounds were applied, transpiration, net photosynthesis, leaf water potential, and soil moisture percentage were determined for treated and control plants. Transpiration and photosynthesis of control plants decreased as the soil dried. Silicone was more effective than ABA in reducing water loss of both species, and was much more effective on Pinus than on Fraxinus. Although silicone had a very positive effect on the water potential of Pinus, photosynthesis of treated plants was greatly reduced with rates of treated plants never exceeding those of control plants. As the drying cycle progressed rates of photosynthesis were higher in ABA-treated Pinus plants than in controls. ABA also significantly increased plant water potential and soil moisture percentage. In Fraxinus, as the drying cycle progressed, both ABA- and silicone-treated plants had lower water stresses than untreated plants. Rates of photosynthesis were higher than in untreated plants. The data indicated that film-forming antitranspirants may be unsuitable for use with some gymnosperms, and that compounds which very significantly decrease transpiration are not necessarily useful and practical in the long term.