Growth impact of O3, NO2 and/or SO2 on pinus taeda

Seedlings of two full-sib families of loblolly pine expressing different degrees of sensitivity to O₃ were exposed to 0.05 ppm O₃, 0.10 ppm NO₂, and/or 0.14 ppm SO₂ for 6 hr/day for 28 consecutive days. The treatments were O₃, NO₂, SO₂ (each used alone), O₃+SO₂, O₃+NO₂, and O₃+NO₂+SO₂. Significant growth suppressions were noted with the relatively sensitive family in all but the the NO₂ alone treatments. The O₃+SO₂ treatment had a more significant effect than O₃ alone, but adding NO₂ had an inconsistent effect. Significant growth suppressions were noted for the relatively non-sensitive family only in the O₃+SO₂ and O₃+SO₂+NO₂ combination treatments. Adding NO₂ to O₃+SO₂ had a slightly stimulatory effect. The relatively sensitive pine family suffered a 30% height growth suppression versus a 14% height growth suppression for the relatively insensitive family when exposed to the 3 pollutant combination. Symptoms were noted on less than 4% of the foliage in the most severe treatments. The pollutant concentrations used in this study were below the National Ambient Air Quality Standards (NAAQS) for each pollutant.