Plasticity in stomatal behavior across a gradient of water supply is consistent among field-grown maize inbred lines with varying stomatal patterning

Stomata regulate leaf CO 2 assimilation ( A ) and water loss. The Ball–Berry and Medlyn models predict stomatal conductance ( g s ) with a slope parameter ( m or g 1 ) that reflects sensitivity of g s to A , atmospheric CO 2 and humidity, and is inversely related to water use efficiency (WUE). This study addressed knowledge gaps about what the values of m and g 1 are in C 4 crops under field conditions, as well as how they vary among genotypes and with drought stress. m and g 1 were unexpectedly consistent in four inbred maize genotypes across a gradient of water supply. This was despite genotypic variation in stomatal patterning, A and g s . m and g 1 were strongly correlated with soil water content, moderately correlated with pre-dawn leaf water potential (Ψ pd ), and weakly correlated with midday leaf water potential (Ψ md ). This implied that m and g 1 respond to long-term water supply more than short-term drought stress. The conserved nature of m and g 1 across anatomically diverse genotypes and water supplies suggests there is flexibility in structure-function relationships underpinning WUE. This evidence can guide simulation of maize g s across a range of water supply in the primary maize growing region and inform efforts to improve WUE. Summary statement Parameter values for models simulating stomatal conductance were unexpectedly consistent for anatomically and physiologically diverse genotypes of the model C 4 crop maize when they were grown across a range of water supplies in the field.