Growth impact of O3, NO2 and/or SO2 on Platanus occidentalis

Seedlings of two half-sib families of American sycamore were exposed to 0.05 ppm O₃, 0.10 ppm NO₂, and/or 0.14 ppm SO₂ for 6 h/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 for both families when exposed to O₃ + SO₂ or O₃ + SO₂ + NO₂. The O₃ + SO₂ treatment had a more significant effect than O₃ alone, and adding NO₂ to the O₃ + SO₂ treatment further suppressed height growth significantly. A 45% and 34% growth suppression was observed for the two families (16-Syc-19 and 16-Syc-23), respectively, in response to the three pollutants in combination. The height growth of both families was significantly suppressed by O₃ alone in some cases. Both families exhibited significant height growth recovery 2 weeks after removal of the pollutant stress. Pollution-induced foliar injury was never evident on the seedlings.