Plant water-use strategy mediates stomatal effects on the light induction of photosynthesis.

More efficient gas exchange strategies under dynamic light environments have been hypothesised to contribute to the dominance of angiosperms in the vascular plant flora. However, we still lack a clear understanding of how stomatal dynamics affect photosynthetic dynamics and whether differences exist between lineages. Stomatal and photosynthetic dynamics following changes in irradiance were studied in 15 species, encompassing ferns, gymnosperms and angiosperms. We determined the effect of stomatal speed on dynamic photosynthesis and water loss. Moreover, we assessed whether dynamic behaviour followed evolutionary lineage divisions, or whether ecological adaptation to maximise light fleck use could describe dynamic behaviour. We found that species with fast stomatal opening, such as ferns, forgo less photosynthesis during photosynthetic induction. By contrast, there was no relationship between stomatal closure speed and the water wasted by transiently more-open stomata, because species with higher rates of gas exchange also showed faster stomatal closure. Shade-adapted species possessed fast-opening but slow-closing stomata, consistent with ecological adaptation to maximise light fleck use. Our results suggest dynamic behaviour follows adaptive ecological trends more strongly than evolutionary ones, but angiosperms may benefit from relatively faster photosynthetic induction by adopting a less conservative water-use strategy.