Foliar injury, leaf gas exchange and biomass responses of black cherry (Prunus serotina Ehrh.) half-sibling families to ozone exposure

Open pollinated families of black cherry seedlings were studied to determin e genotypic differences in foliar ozone injury and leaf gas exchange in 199 4 and growth response following three growing seasons. An O-3-sensitive hal f-sibling family (R-12) and an O-3-tolerant half-sibling family (MO-7) plan ted in natural soil were studied along with generic nursery stock (NS) seed lings. Ozone exposure treatments were provided through open top chambers an d consisted of 50, 75, and 97% of ambient ozone, and open plots from May 9 to August 26, 1994. Ambient ozone concentrations reached an hourly peak of 85 ppb with 7-hour averages ranging from 39 to 46 ppb. Seedlings in the 50 and 75% of ambient chambers were never exposed to greater than 80 ppb O-3. Visible foliar ozone injury (stipple) was significantly higher for R-12 see dlings than MO-7 seedlings and increased with increasing ozone exposures. F or the chamber treatments averaged over all families, there was no signific ant difference in stomatal conductance and net photosynthetic rates, but th ere was a significant decrease in root biomass, and a significant decrease in root/shoot ratio between the 50 and 97% of ambient chambers. Stomatal co nductance and net photosynthetic rates were significantly different between families with R-12 seedlings generally greater than MO-7 seedlings. The R- 12 seedlings had a 7.5 mmol m(-2) increase in ozone uptake compared to MO-7 , and at the same cumulative O-3 exposure R-12 exhibited 40.9% stippled lea f area, whereas MO-7 had 9.2% stippled leaf area. Significant differences w ere observed in stem volume growth and total final biomass between the open -top chambers and open plots. Although R-12 had the most severe foliar ozon e injury, this family had significantly greater stem volume growth and tota l final biomass than MO-7 and NS seedlings. Root:shoot ratio was not signif icantly different between MO-7 and R-12 seedlings. (C) 1999 Elsevier Scienc e Ltd. All rights reserved.