The Influences of Stomatal Size and Density on Rice Drought, Salinity and VPD Resilience

Summary A warming climate coupled with reductions in water availability and rising salinity are increasingly affecting rice yields ( Oryza sativa L.). Elevated temperatures are causing vapour pressure deficit (VPD) rises, leading to stomata closure, further reducing plant productivity and cooling. It is unclear which conformation of stomatal size (SS) and stomatal density (SD) will best suit these future environmental extremes. To understand the influence of stomatal characteristics on rice abiotic stress tolerance, we screened the stomatal characteristics of 72 traditionally-bred varieties. We found significant variation in SS, SD and maximal stomatal conductance ( g smax ) but did not identify any varieties with SD and g smax as low as the genetically manipulated stomatal development mutant OsEPF1oe . Traditionally-bred varieties with high SD and small SS (resulting in high g smax ) typically had lower biomasses, and these plants were more resilient to drought than low SD and large SS plants, which were physically larger. None of the varieties tested were as resilient to drought or salinity as low SD OsEPF1oe mutants. High SD and small SS rice displayed faster stomatal closure during rising VPD, but photosynthesis and plant cooling were reduced. Compromises will be required when choosing rice SS and SD to tackle multiple future environmental stresses.