Effects of CO2 enrichment on growth and photosynthesis in Desmodium paniculatum

Plants of Desmodium paniculatum (Leguminosae) were grown from seeds in normal air (0.035% CO 2 ) and in air containing 0.1% CO 2 . CO 2 enrichment produced an almost twofold increase in dry matter production. Leaf areas were 1.2 times higher at high CO 2 . Relative growth rates under high CO 2 were significantly higher during the early stages of development and then declined. The increase in dry matter production was not associated with an increase in photosynthetic capacity per unit leaf area. Gas exchange measurements indicated that plants from the high CO 2 regime had lower light saturation values and lower photosynthetic rates at high quantum flux densities than the controls. An opposite trend was observed if gas exchange rates were expressed on a chlorophyll basis. The depression in photosynthetic rates on a leaf area basis of plants exposed to CO 2 enrichment was correlated with increased starch accumulation and reduced grana formation in chloroplasts of leaves continuously exposed to high CO 2 concentrations.