Leaf photosynthesis and carbohydrate dynamics of soybeans grown throughout their life-cycle under Free-Air Carbon dioxide Enrichment

A lower than theoretically expected increase in leaf photosynthesis with long-term elevation of carbon dioxide concentration ([CO 2 ]) is often attributed to limitations in the capacity of the plant to utilize the additional photosynthate, possibly resulting from restrictions in rooting volume, nitrogen supply or genetic constraints. Field-grown, nitrogen- fixing soybean with indeterminate flowering might therefore be expected to escape these limitations. Soybean was grown from emergence to grain maturity in ambient air (372 m mol mol- 1 [CO 2 ]) and in air enriched with CO 2 (552 m mol mol- 1 [CO 2 ]) using Free-Air CO 2 Enrichment (FACE)technology. The diurnal courses of leaf CO 2 uptake ( A ) and stomatal nductance ( g s ) for upper canopy leaves were followed throughout development from the appearance of the first true leaf to the completion of seed filling. Across the growing season the daily integrals of leaf photosynthetic CO 2 uptake ( A ¢ ) increased by 24.6