Interaction of Ozone with Simultaneous Water Deficit and Water Deficit Preconditioning in One-year-old Pinus densiflora Seedlings

Abstract

The primary objective of this study was to investigate if responses of potted Pinus densiflora Sieb. et Zucc. seedlings to ozone exposure could be altered by water deficit stress applied before or during ozone exposure. One-year-old seedlings grown from seeds in pots were used. Water deficit preconditioning was done for ten weeks from May 1, 1998, followed by ozone exposure and simultaneous water deficit for eight weeks. Water deficit was controlled by monitoring xylem water potentials with a pressure chamber. Ozone was fumigated in open top chambers with an eight-hour mean concentration of 0.1 ppm. A 23 factorial design was employed. Dry weights, carbohydrate concentrations, and leaf gas exchanges were measured. In response to the water deficit, growth and stomatal conductance were reduced, while soluble carbohydrate concentrations were enhanced. Interactions between ozone and simultaneous water deficit were significant. Dry weights were significantly decreased by ozone exposure only in well-watered seedlings, suggesting that simultaneous water deficit may alleviate the adverse effects of ozone. This protection from ozone stress observed in water-stressed seedlings resulted from: (1) reduced ozone uptake due to stomatal closure and (2) enhanced TNC (Total Nonstructural Carbohydrates) which acted as a buffer against ozone injury.