Effects of kinetics of light-induced stomatal responses on photosynthesis and water-use efficiency

Both photosynthesis (A) and stomatal conductance (g(s)) respond to changing irradiance, yet stomatal responses are an order of magnitude slower than photosynthesis, resulting in noncoordination between A and g(s) in dynamic light environments. Infrared gas exchange analysis was used to examine the temporal responses and coordination of A and g(s) to a step increase and decrease in light in a range of different species, and the impact on intrinsic water use efficiency was evaluated. The temporal responses revealed a large range of strategies to save water or maximize photosynthesis in the different species used in this study but also displayed an uncoupling of A and g(s) in most of the species. The shape of the guard cells influenced the rapidity of response and the overall g(s) values achieved, with different impacts on A and W-i. The rapidity of g(s) in dumbbell-shaped guard cells could be attributed to size, whilst in elliptical-shaped guard cells features other than anatomy were more important for kinetics. Our findings suggest significant variation in the rapidity of stomatal responses amongst species, providing a novel target for improving photosynthesis and water use.