Nighttime transpirational cooling enabled by circadian regulation of stomatal conductance is related to stomatal anatomy and leaf morphology in rice

Main conclusion Rice genotypes with larger stomata maintain higher nocturnal stomatal conductance, thus having lower nocturnal leaf temperature via transpirational cooling. Incomplete night stomatal closure has been widely observed, but the mechanisms and functions of nocturnal stomatal conductance ( g s,n ) are not fully understood. Stomatal anatomy, leaf morphology, g s,n and nocturnal leaf temperature ( T leaf,n ) were measured in 30 Oryza genotypes. Nocturnal leaf conductance ( g n ) showed a significant circadian rhythm; it gradually increased by 58% from 20:30 to 04:30. Contrary to cuticular conductance ( g cut ), g s,n was highly correlated with g n . Moreover, g s,n accounted for 76% of g n . T leaf,n was significantly lower than the air temperature, and was negatively correlated with both g s,n and nocturnal transpiration rate ( E n ). g s,n was positively correlated with stomatal size, intervein distance between major veins (IVD major ), leaf thickness (LT), individual leaf area (LA), and leaf width (LW). It was also found negatively correlated with stomatal density. Reversely, T leaf,n was negatively correlated with stomatal size, IVD major , intervein distance between minor veins, LA and LW. T leaf,n presented a positive correlation with stomatal density. This study highlights the importance of stomatal anatomy and leaf morphology on regulating g s,n and T leaf,n . The underlying mechanisms to the determinants of g s,n and the physiological and ecological functions of the T leaf,n regulation on rice growth and production were carefully discussed.