Unexpected Responses of Bean Leaf Size to Elevated CO(2)

CO(2) is currently a growth-limiting resource for plants with C(3) metabolism, and elevated CO(2) also often reduces stomatal conductance, reducing plant water stress. Increased photosynthesis and improved water status might be expected to result in increased leaf size. It is therefore unexpected that leaf size is in some cases reduced in plants grown at elevated CO(2), and also unexpected that elevated CO(2) applied only during darkness can increase leaf size. These experiments compared leaf size responses to day and/or night elevated CO(2) in six cultivars of Phaseolus vulgaris grown with either constant or varying temperature in controlled environment chambers. Diverse responses of leaf size to elevated CO(2) were found among the cultivars, including increased leaf size with elevated CO(2) applied only during darkness in some cultivars and temperature regimes. However, leaf size responses to elevated CO(2) and cultivar differences in response were unrelated to differences in leaf water potential or turgor pressure.