The effect of ozone on gas-exchange: A comparison of invasive and native tree species

Background/Question/Methods Ground-level ozone can have toxic effects on plants, and variation among trees in their tolerance of ozone could lead to changes in community composition in heavily polluted areas. This could result in the loss of some species and potentially provide opportunities for invasive species. I examined the effects of ozone on gas exchange in 13 species of trees common in the Mid-Atlantic, including 8 native and 5 invasive species. Saplings planted in three blocks within a common garden at Blandy Experimental Farm (Clarke County, VA) were exposed to three ozone treatments during the summer of 2008. Each trial consisted of a triplet of a single species, where each individual received a separate ozone treatment (7.5x, 3.8x, ambient) from 1000-1800 EDT. Gas exchange data (carbon assimilation, ozone uptake, and transpiration) were continuously collected for each treatment. Results/Conclusions Species showed higher ozone uptake values in the high treatments than the medium or low treatments. Cumulative ozone uptake differed among species (χ2=2.978, p=0.04). Stomatal conductance values also showed differences among species (χ2 = 3.558, p=0.03), as did both intercellular levels of carbon dioxide (χ2 = 25.459, p<0.0001) and ozone uptake rates (χ2 = 3.779, p=0.03). All species showed significant negative correlations between carbon assimilation and cumulative ozone uptake in the high ozone treatment. Species showed marginally significant differences in their stomatal conductance and carbon assimilation responses to ozone treatments (χ2 = 2.70, p = 0.05, and χ2 = 2.36, p = 0.06, respectively). Comparisons of invasive and native species failed to show significant differences between the two groups. The results indicate species-specific differences in response to ozone and may point towards evidence for ozone tolerance.