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 development are important determinants of plant photosynthetic capacity, The interactive effects of photon flux density (PFD), nitrogen supply and CO2 concentration on leaf expansion rate were measured as well as final leaf size and thickness of soybean, Leaf thickness and final area were not correlated with leaf relative expansion rate (RER) suggesting that these parameters are controlled by different mechanisms and that final leaf dimensions are determined by the duration rather than the rate of leaf expansion, Carbohydrate supply did not explain the variation ii? leaf RER since RER increased with increasing CO2 concentration, but decreased with increasing PFD. Leaf thickness and final area were related to resource supply but not in a simple fashion, Both positive and negative correlations between leaf thickness and carbohydrate and nitrogen concentrations were obtained depending on the environmental variable responsible for the variation. In contrast, there was a simple proportional relationship between whole plant relative growth rate and a correlate of leaf thickness (leaf water content per unit area), suggesting that leaf thickness responds to the balanced supply of all resources, in the same fashion as RGR, rather than to any individual resource.