Ozone, acidic rain and soil magnesium effects on growth and foliar pigments of Pinus taeda L.

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Abstract
Height and diameter growth, biomass accumulation and leaf pigment concentrations were measured in loblolly pine (Pinus taeda L.) seedlings grown in soil containing 12 or 35 μg Mg g−1 and exposed from May to October to subambient, ambient, or twice-ambient ozone (O3), and to simulated acidic rain with a pH of either 4.0 or 5.3. At the end of one growing season, height and diameter growth of seedlings exposed to twice-ambient O3 were not statistically different from those of seedlings exposed to subambient O3. Biomass of all plant parts was reduced by 7 to 16% in response to increasing O3 concentration. No statistically significant growth responses to rain chemistry or soil magnesium status were observed, and there were no statistically significant interactive treatment effects. Needle pigment concentrations were not significantly affected by rain chemistry or soil Mg status and there were no visible signs of injury to needles that could be attributed to O3 stress or Mg deficiency. Concentrations of chlorophyll a and b, and carotenes were 23, 30 and 21% higher (P ≤ 0.05) respectively, in seedlings exposed to twice-ambient O3 than in seedlings from the other ozone treatments. There were no interactive treatment effects on needle pigment concentrations.

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