Effects of Soil Drought with Nocturnal Warming on Leaf Stomatal Traits and Mesophyll Cell Ultrastructure of a Perennial Grass

While water deficit and rising temperatures are progressive global problems, their combined effect on plants has received less attention. Stomatal traits, mesophyll cell ultrastructure, net photosynthetic rate, lipid peroxidation, and ion leakage were examined in leaves of Leymus chinensis (Trin.) Tzvel. plants using native Castanozem soil. Stomatal traits and mesophyll cell ultrastructure were studied using light microscopy and transmission electron microscope. Under severe water stress, malondialdehyde and ion leakage increased, especially at high night temperatures of 30/25 degrees C (day/night). Mild water stress increased stomatal density, especially with normal night temperatures of 30/20 degrees C (day/night). Moderate and severe water stress did not affect stomatal density. Under water stress, mesophyll cell ultrastructures were disturbed, and the membrane systems of chloroplasts and mitochondria were broken, particularly at high night temperatures. Leaf net photosynthetic rate and stomatal conductance were negatively correlated with ion leakage and malondialdehyde. The results suggested that high night temperature may aggravate the adverse effects of soil water deficit on leaf stomatal traits and mesophyll cell ultrastructure and also enhance lipid peroxidation.