Elevated CO2 concentration has independent effects on expansion rates and thickness of soybean leaves across light and nitrogen gradients

The rate and extent of leaf thickness and area development are importantdeterminants of whole plant photosynthetic capacity. The interactiveeffects of photon flux density (PFD), nitrogen supplyand CO2 concentration on leaf expansion rate were measured as well as finalleaf size and thickness of soybean. Leaf thickness and final area were notcorrelated with leaf relative expansion rate (RER)suggesting that these parameters are controlled by different mechanisms andthat final leaf dimensions are determined by the duration rather than therate of leaf expansion. Carbohydrate supply did not explain the variationin leaf RER since RER increasedwith increasing CO2 concentration, but decreased with increasingPFD. Leaf thickness and final area were related toresource supply but not in a simple fashion. Both positive and negativecorrelations between leaf thickness and carbohydrate and nitrogenconcentrations were obtained depending on the environmental variableresponsible for the variation. In contrast, there was a simple proportionalrelationship between whole plant relative growth rate and a correlate ofleaf thickness (leaf water content per unit area), suggesting that leafthickness responds to the balanced supply of all resources, in the samefashion as RGR, rather than to any individualresource.