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Environmental and Stress Physiology

SO₂ Effect on Photosynthetic Activities of Intact Sugar Maple Leaves as Detected by Photoacoustic Spectroscopy ¹

Centre de recherche en photobiophysique, Université du Québec à Trois-Rivières, C.P. 500, Trois-Rivières (Québec), G9A 5H7, Canada

Short-term (4 hours) effect of different concentrations of SO₂ fumigation on in vivo photochemical activities of sugar maple (Acer saccharum Marsh.) leaves was investigated using photoacoustic spectroscopy. The relative quantum yield of O₂ evolution (ratio of O₂ signal to the photothermal signal) and photochemical energy storage are increased by 0.05 microliter per liter of SO₂. This increase is more pronounced in 5 to 7 year old saplings than in 3 month old seedlings. Both oxygen-relative quantum yield and energy storage of seedlings are inhibited by increased concentrations of SO₂ and the inhibition is concentration dependent. The inhibition is greater in seedlings than in saplings at 2 microliters per liter of SO₂, indicating the more susceptible nature of seedlings. The present study indicates a concentration dependent differential effect of SO₂ on photochemical activities of sugar maple leaves.