Nocturnal stomatal conductance in wheat is growth‐stage specific and shows genotypic variation

Summary Nocturnal stomatal conductance ( g sn ) represents a significant source of water loss, with implications for metabolism, thermal regulation and water‐use efficiency. With increasing nocturnal temperatures due to climate change, it is vital to identify and understand variation in the magnitude and responses of g sn in major crops. We assessed interspecific variation in g sn and daytime stomatal conductance ( g s ) in a wild relative and modern spring wheat genotype. To investigate intraspecific variation, we grew six modern wheat genotypes and two landraces under well watered, simulated field conditions. For the diurnal data, higher g sn in the wild relative was associated with significantly lower nocturnal respiration and higher daytime CO 2 assimilation while both species exhibited declines in g sn post‐dusk and pre‐dawn. Lifetime g sn achieved rates of 5.7–18.9% of g s . Magnitude of g sn was genotype specific 'and positively correlated with g s . g sn and g s were significantly higher on the adaxial surface. No relationship was determined between harvest characteristics, stomatal morphology and g sn , while cuticular conductance was genotype specific. Finally, for the majority of genotypes, g sn declined with age. Here we present the discovery that variation in g sn occurs across developmental, morphological and temporal scales in nonstressed wheat, presenting opportunities for exploiting intrinsic variation under heat or water stressed conditions.