Effects of CO2 enrichment on growth and photosynthesis in Desmodium paniculatum

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Abstract
Plants of D. paniculatum (Leguminosae) were grown from seeds in normal air (0.035% CO2) and in air containing 0.1% CO2. CO2 enrichment produced an almost 2-fold increase in dry matter production. Leaf areas were 1.2 times higher at high CO2. Relative growth rates under high CO2 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 CO2 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 CO2 enrichment was correlated with increased starch accumulation and reduced grana formation in chloroplasts of leaves continuously exposed to high CO2 concentrations.