Understanding Leaf Surface-Specific Stomatal Traits and Their Effects on Barley Grain Yield

Spring barley yields are highly variable, depending mostly on early season precipitation and temperature. Stomatal traits (stomatal conductance, size, density, adaxial to abaxial stomatal density ratio and conductance ratio) are important determinants of plant production and stress tolerance. Here, we determined stomatal traits of penultimate and flag leaves and grain yields of thirteen barley genotypes during a 3-year field experiment in Estonia. We found that adaxial to abaxial stomatal density ratio was mostly determined by environment in penultimate leaves. Grain yields ranged from 2400 to 6100 kg ha^-1 in our study. Correlations between stomatal traits and grain yield were found in the pooled dataset due to strong effects of annual abiotic conditions on studied traits. Penultimate leaf ratios of adaxial to abaxial stomatal density and conductance correlated positively with grain yield in the pooled dataset. In 2022 and 2023, the stomatal conductance ratio also correlated with grain yield, however, no other stomatal trait correlated with grain yield in any individual year, although stomatal traits differed significantly between genotypes. Thus, stomatal traits of barley penultimate leaves and their association with yield are largely driven by environmental variation and coordinated stomatal trait responses of leaf surfaces to abiotic environment are important for barley adaptation.