Fast stomatal kinetics in sorghum enable tight coordination with photosynthetic responses to dynamic light intensity and safeguard high water use efficiency.

In this study, we assessed 43 accessions of sorghum from 16 countries across three continents. Our objective was to identify stomatal and photosynthetic traits that could be exploited in breeding programmes to increase photosynthesis without increasing water use under dynamic light environments. Under field conditions, sorghum crops often have limited water availability and are exposed to rapidly fluctuating light intensities, which influences both photosynthesis and stomatal behaviour. Our results highlight a tight coupling between photosynthetic rate (A) and stomatal conductance (gs) even under dynamic light conditions that results in steady intrinsic water use efficiency (Wi). This was mainly due to rapid stomatal responses, with the majority of sorghum accessions responding within ≤5 min. The maintenance of the ratio of the concentration of CO2 inside the leaf (Ci) and the surrounding atmospheric concentration (Ca) over a large range of accessions suggests high stomatal sensitivity to changes in Ci, that could underlie the rapid gs responses and extremely close relationship between A and gs under both dynamic and steady-state conditions. Therefore, sorghum represents a prime candidate for uncovering the elusive mechanisms that coordinate A and gs, and such information could be used to design crops with high A without incurring significant water losses and eroding Wi.