Correlative Reductions in Whole-Plant Photosynthesis and Yield of Winter Wheat Caused by Ozone

Abstract

Winter wheat [Triticum aestivum] (cultivar Vona) was exposed to four levels of O3 (7-hr exposure period averages of 0.027, 0.054, 0.076, and 0.096 ppm) and four levels of SO2 (4-hr exposure period averages of 0, 0.039, 0.166, and 0.363 ppm) and all combinations of the two pollutants from anthesis until harvest. Sulfur dioxide did not affect net photosynthesis or yield but temporarily reduced stomatal conductances of flag leaves. No interactions between SO2 and O3 were found for any variables measured. Ozone accelerated the senescence of flag leaves, stalks, and heads and also accelerated the loss of moisture from the heads. Ozone significantly reduced stomatal conductances of flag leaves, net photosynthesis of whole plants and individual heads, and seed dry weights per head as a result of reduced seed size but not seed number. Reductions in seed weights caused by ozone were highly correlated with measured reductions in whole-plant and individual head photosynthesis. Exposure of Vona winter wheat to ambient and higher O3 concentrations from anthesis until harvest resulted in yield losses caused by reductions in net photosynthesis.