A preliminary study of the response of red spruce to O3 and SO2

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A laboratory branch chamber experiment determined the response of a young red spruce (Picea rubens) sapling to ozone (O3) and sulfur dioxide (SO2). A treatment branch was exposed to concentrations of O3 (∼ 90 ppbv) and SO2 (∼ 15 ppbv) representative of the summertime maxima observed in the high elevation spruce-fir forests of the eastern United States. A control branch of the same age and comparable biomass received clean air only. Pollution exposure, lasting 78 days, consisted of 4 sequential stages designed to compare the tree's response to each individual pollutant with its response to the combination of SO2 + O3. The treatment branch exhibited distinctly different physiological responses to O3 alone, SO2 alone, and the SO2 + O3 combination. Ozone exposure in the 1st stage induced an increase in CO2 assimilation (20% over 26 days, relative to the control branch) while transpiration and nighttime respiration were unaffected. Ozone uptake increased markedly during this stage. In the 16-day 2nd stage of exposure, the combination of SO2 + O3 induced a factor of ∼ 2 decrease in CO2 assimilation, transpiration and O3 uptake within 1 week. In the 3rd stage, the removal of SO2 resulted in the partial recovery of photosynthetic uptake and other gas fluxes. A final stage of exposure to SO2 alone produced large day-to-day variations in CO2 assimilation. The isoprene emission rate of the treatment branch declined relative to the control branch over the course of the entire experiment. The results of this preliminary experiment suggest that, singly and in combination, O3 and SO2 may disrupt physiological functions of red spruce. Further experiments are needed to determine whether these results pertain to larger populations of red spruce and the occurrence of red spruce decline in the northeastern United States.DOI: 10.1034/j.1600-0889.1993.00004.x
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