Relationship between leaf morphology and physiological responses of perennial ryegrass under cold stress

Perennial ryegrass(Lolium perenne) is susceptible to cold and windy condition in winter, which results in dehydration and death. In order to explore the relationship between leaf morphology and physiological changes of perennial ryegrass under cold stress, leaf morphology, relative water loss rate of detached leaves and some physiological indices under cold stress 0 ℃ of cultivar 'Brightstar SLT' (freezing-tolerant) and 'Linn' (freezing-sensitive) were measured. Under natural condition, the stomatal number of 'Brightstar SLT' was significantly higher than (P<0.05) that of 'Linn', whereas stomatal length, stomatal area, leaf epidermal cell and leaf relative water loss of 'Brightstar SLT' were significantly lower than (P<0.05) those of 'Linn'. Under cold stress, transpiration rate and stomatal conductance of both perennial ryegrass cultivars increased in a short time, however, those of the 'Brightstar SLT' were significantly lower (P<0.05) than those of 'Linn'. In addition, the photosynthetic rate of 'Brightstar SLT' was significantly higher (P<0.05) than that of 'Linn', whereas electrolyte leakage of 'Brightstar SLT' was lower than that of 'Linn'. In conclusion, there was a close correlation between lower water loss rate along with better performance under cold stress (including stable photosynthesis ability and less cold injury) and leaf morphology (including larger quantity of stoma, shorter stomatal length, smaller stomatal size and smaller leaf epidermal cell) in freezing-tolerant cultivar.