Chlorophyll reduction in western wheatgrass (Agropyron smithii Rydb.) exposed to sulfur dioxide

Chlorophyll concentrations in western wheatgrass, an important dominant species in the grasslands of the northern Great Plains of North America, exposed to controlled SO₂ concentrations were examined. Concentrations of chlorophylls a and b were significantly decreased, without visible plant necrosis. Chlorophyll-a was more sensitive than chlorophyll-b. Sensitivity of chlorophylls to SO₂ changed as the growing season progressed, indicating cumulative effects and interactions with normal senescence.