Effects of ozone and acid rain on white pine (Pinus strobus) seedlings grown in five soils. I. Net photosynthesis and growth

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Abstract
Four replicated factorial experiments were conducted to assess the response of potted white pine (Pinus strobus L.) seedlings to combined acid rain, ozone, and soil treatments. The objectives of the study were to quantify plant response to each pollutant alone and to determine whether the pollutants and edaphic factors interact in affecting physiological processes in white pine. In these studies, seedlings were grown in five forest soils and exposed for 4 months to realistic levels of acid rain and ozone. Acid rain treatments consisted of exposure to simulated rain of pH 5.6, 4.0, 3.5, or 3.0, while ozone treatments consisted of exposure to 0.02, 0.06, 0.10, or 0.14 ppm ozone. Minimal interaction between acid rain and ozone was observed with regard to photosynthesis or growth. Acid rain and soil type had a strong interaction in determining plant response. In general, acid rain caused increased growth and net photosynthesis as a result of nitrogen fertilization from the simulated rain. However, the extent of this response was inversely correlated with the availability of nitrogen in each soil. Ozone treatments caused decreased net photosynthesis in pine seedlings.