Morphological responses among crop species to full-season exposures to enhanced concentrations of atmospheric CO₂ and O₃

Abstract

Field studies using open-top chambers were conducted at USDA-BARC involving the growth of soybeans ('89 & '90), wheat ('91 & '92), and corn ('91), under increased concentrations of atmospheric CO₂ and O₃. Treatment responses were compared in all cases to plants grown in charcoal-filtered (CF) air (seasonal 7-h mean = 25±3 n mol O₃ mol⁻¹) having 350 or 500 μ mol CO₂ mol⁻¹. Elevated seasonal O₃ levels for the soybean, wheat, and corn studies averaged 72.2±4, 62.7±2, and 70.2 n mol O₃ mol⁻¹, respectively. Results presented were obtained for plants grown in silt loam soil under well-watered conditions. Grain yield increases in response to elevated CO₂ in the absence of O₃ stress averaged 9.0, 12.0, and 1.0% for soybean, wheat, and corn; respectively. Reductions in grain yields in response to the elevated O₃ treatments at 350 μ mol CO, mol⁻¹ averaged 20.0, 29.0 and 13.0% for soybean, wheat, and corn, respectively. Reductions in grain yields in response to elevated O₃ at 500 μ mol CO₂ mol⁻¹ averaged 20.0, 8.0, and 7.0% for soybean, wheat, and corn, respectively. Dry biomass and harvest index in wheat were significantly reduced by O₃ stress at 350 μ mol mol ¹ CO₂ but not at 500 u mol mol⁻¹ CO₂. Seed weight 1000⁻¹ for scybeans and wheat was significantly increased by CO₂ enrichment and decreased by O₃ stress. Seed weight 1000⁻¹ in corn was increased by O₃ stress suggesting that O₃ affected pollination resulting in fewer kernels per ear.