Photosynthetic pigment levels in soybean increased when exposed to higher levels of carbon dioxide. Chlorophyll and carotenoid contents rose significantly under elevated CO2 concentrations, with increases ranging from 4.3% to 14.1% for chlorophyll and 6.8% to 24.6% for carotenoids. Both chlorophyll a and b levels also increased, but the ratio of chlorophyll a to b decreased at higher CO2 levels.