Stomatal conductance modulates maize yield through water use and yield components under salinity stress

Drought or/and salinity stress significantly impact maize water use and production. However, comprehensive investigations into the genotype × environment interactions (water or/and salinity) on maize growth, water use, and water productivity (WP) and the physiological controlling factors governing maize production remain lacking. In the present study, we rigorously investigated the effect of water or/and salinity on leaf physiological and morphological characteristics, evapotranspiration (ET), yield and its components (kernel number, KN; thousand kernel weight, TKW) for two genotypes (XY335 and ZD958) over two years, and revealed the mechanisms of yield response to these traits. We found that stomatal conductance (gs) and net photosynthesis rate (A), aboveground biomass (AGB), ET, and KN were higher in XY335 compared to those in ZD958 in both years. Water and salinity stress reduced gs, A, leaf area (LA), the fraction of canopy radiation interception (fPAR), AGB, ET, yield, and KN, while increasing intrinsic water use efficiency. Simultaneous water and salinity stress exhibited an antagonistic effect on WP. Yield was modulated by both ET and yield components. ET was mainly regulated by LA, and only KN was driven by A under salt-free condition. However, under salinity stress, ET was jointly regulated by gs and fPAR, and both gs and A affected KN and TKW. Importantly, a decrease in ET induced by stress did not always lead to yield reduction, provided the reduction remained below about 20% of the maximum value. Thus, mildly regulated deficit irrigation or adapting to low-concentration soil salinity stress was preferable for sustaining yield and improving WP. Nevertheless, a combination of both approaches diminished the water-saving benefits of individual farmland management practices. This study filled the knowledge gap regarding the physiological mechanisms of driving yield variations and offered valuable insights for effective crop water management in drought and soil-salinized regions.