Alterations in Soybean Leaf Development and Photosynthesis in a Co2- Enriched Atmosphere

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Abstract
This study was conducted to characterize changes in the canopy photosynthetic leaf area of developing soybean (Glycine max [L.] Merr. cv Lee) exposed to a CO2-enriched atmosphere. Young, vegetative plants were exposed to 350 or 700 .mu.L L-1 CO2 for 15 d. Plant dry mass and total leaf area were greater in the CO2-enriched environment. Emergence and expansion rates of main stem leaves increased at high CO2, but the areas of individual leaves at full expansion were affected very little (5%-10% greater than controls). More rapid leaf expansion rates occurred in the light and dark. Under CO2-enriched conditions, the net CO2 exchange rates of all leaves on the main stem were higher before and after full expansion. Stomatal conductance was lower in high CO2 only after leaves approached full expansion. Leaf development on the lateral branches also was increased at high CO2, accounting for 40% of the total increase in leaf area by the end of the experiment. We conclude that more rapid rates of leaf development under CO2 enrichment likely resulted from increased photosynthesis rates and that both direct and indirect effects were involved.