Salinity-specific stomatal conductance model parameters are reduced by stomatal saturation conductance and area via leaf nitrogen

Modeling stomatal behavior is necessary for accurate stomatal simulation and predicting the terrestrial water‑carbon cycle. Although the Ball-Berry and Medlyn stomatal conductance (gs) models have been widely used, variations and the drivers of their key slope parameters (m and g1) remain poorly understood under salinity stress. We measured leaf gas exchange, physiological and biochemical traits, soil water content and electrical conductivity of saturation extract (ECe), and fitted slope parameters of two genotypes of maize growing in two water and two salinity levels. We found m was different between the genotypes, but no difference in g1. Salinity stress reduced m and g1, saturated stomatal conductance (gsat), the fraction of leaf epidermis area allocation to stomata (fs), and leaf nitrogen (N) content, and increased ECe, but no marked decrease in slope parameters under drought. Both m and g1 were positively correlated with gsat, fs, and leaf N content, and negatively correlated with ECe in the same fashion among the two genotypes. Salinity stress altered m and g1 by modulating gsat and fs via leaf N content. The prediction accuracy of gs was improved using salinity-specific slope parameters, with root mean square error (RMSE) being decreased from 0.056 to 0.046 and 0.066 to 0.025 mol m−2 s−1 for the Ball-Berry and Medlyn models, respectively. This study provides a modeling approach to improving the simulation of stomatal conductance under salinity.