Stomatal conductance parameters of tomatoes are regulated by reducing osmotic potential and pre-dawn leaf water potential via increasing ABA under salt stress

The opening and closing of stomata control the diffusion of CO2 and water vapor, and accurate modeling of stomatal conductance (gs) is essential for predicting global water and CO2 fluxes. The Ball-Berry and Medlyn models with key slope parameters (m or g1) have been widely used to estimate gs. However, there are few studies on quantifying the model parameter values of different tomato genotypes and analyzing their relationship with physiological traits under salt stress. Here, we fit m and g1 of tomatoes using stomatal response curves and analyzed their correlations with physiological characteristics under five genotypes and two salt treatments. m was significantly different while g1 was more stable among genotypes, and salt stress significantly reduced them. By testing differences in regression slopes or intercepts, the relationships between leaf water status, and biochemical and stomatal development are found to be uniform among tomato genotypes. Osmotic potential, pre-dawn leaf water potential and abscisic acid (ABA) are driving factors for gs model parameters. Structural equation modeling showed that ABA directly modulates model parameters, not through leaf morphology or stomatal development. Overall, this study quantified gs model parameters and identified driving factors for different tomato genotypes under salt stress, providing a practical approach to model water and carbon fluxes under salt stress.