Photosynthetic carbon dioxide exchange of bean plants grown at elevated carbon dioxide concentrations

Leaves of bean plants (Phaseolus vulgaris L. cv. Pure Gold Wax) grown in atmospheres enriched in CO2 (1400 μL L−1) showed a decrease in CO2 exchange capacity when compared with unenriched plants (340 μL L−1) measured at the same CO2 concentration. The decrease was not associated with changes in chlorophyll concentration or photorespiratory activity. The decrease was less evident in older leaves, in leaves maintained at low light intensity, and in those with reduced chlorophyll contents. Respiration rates in leaves of CO2-enriched plants increased only under conditions that caused a concurrent decrease in photosynthetic capacity. Enriched leaves had higher starch contents than unenriched leaves. The results were consistent with the idea that CO2 enrichment decreases photosynthetic capacity when photoassimilate supply exceeds sink demand.