The impact of stomatal kinetics on diurnal photosynthesis and water use efficiency under fluctuating light

Abstract

AbstractDynamic light conditions require continuous adjustments of stomatal aperture. As stomatal conductance (gs) kinetics are a magnitude slower than photosynthesis (A), they are hypothesized to be key to plant productivity and water use efficiency. Using step-changes in light intensity, we studied the diversity of light-induced gs kinetics in relation to stomatal anatomy in five banana genotypes (Musa spp.) and modelled the impact on A and intrinsic water use efficiency (iWUE). Banana generally exhibited a strong limitation of A by gs, indicating a priority for water saving. Significant genotypic differences in gs kinetics and gs-based limitations of A were observed. For two contrasting genotypes the impact of differential gs kinetics on A and iWUE was further investigated under realistic diurnally fluctuating light conditions and at whole-plant level. Genotype-specific stomatal kinetics observed at the leaf level were corroborated at whole-plant level, suggesting that despite differences in gs control at different locations in the leaf and across leaves, genotype-specific responses are still maintained. However, under diurnally fluctuating light conditions gs speediness had only a momentary impact on the diurnal iWUE and carbon gain. During the afternoon there was a setback in kinetics: the absolute gs and the gs responses to light were damped, strongly limiting A and the diurnal iWUE. We conclude that the impact of the differential gs kinetics on the limitation of A was dependent on the target light intensity, the magnitude of change, the gs prior to the intensity change and particularly the time of the day.One sentence summaryGenotype-specific stomatal rapidity is for the first time validated at whole-plant level, but under fluctuating light the impact of stomatal dynamics depends on other factors like the time of the day.