Gas exchange and water relations of Fraxinus americana affected by flurprimidol.

Effects of flurprimidol on plant water relations and leaf gas exchange were investigated in one-year-old white ash (Fraxinus americana L.) seedlings subjected to soil water deficits. Flurprimidol (20 mg kg(-1) of soil equivalent) was applied to the soil surface of pot-grown seedlings after shoot growth was completed. Two months after flurprimidol application, water was withheld from one-half of the seedlings. Leaf water relations and gas exchange parameters were measured 5, 7, 10, 14, 18 and 22 days after withholding water. Under both irrigated and nonirrigated conditions, flurprimidol treatment resulted in reduced net CO(2) assimilation rate and transpirational water loss of seedlings as a result of decreased stomatal conductance. Consequently, flurprimidol-treated seedlings had higher leaf water potential and relative water content than untreated seedlings. Nonirrigated flurprimidol-treated seedlings also had greater turgor and sap osmolality and lower osmotic potential at full turgor than seedlings in the other treatments, indicating that flurprimidol increased osmotic adjustment. Under water-stress conditions, water use efficiency was lower and gas exchange efficiency was higher in flurprimidol-treated seedlings than in untreated seedlings, suggesting that flurprimidol treatment enhances survival of plants subjected to soil water deficits.