Effects of urban heat island intensity on leaf water-relevant traits of greening tree species with different leaf textures

Objective This paper aims to explore the response of water content correlation between two different leaf textures to urban heat islands, and to reveal whether there are differences in the adaptation methods of varied leaf textures to urban heat islands.

Method In four typical heat island intensity plots in Beijing, common chartaceous and coriaceous leaf greening tree species were used as objects to study the changes in leaf vein, stomatal traits, and leaf epidermal thickness related to tree water processes.

Result (1) The leaf vein density, stomatal density, stomatal length, maximum stomatal conductivity, and upper epidermal thickness of chartaceous leaves showed an increasing trend in the strong heat island area compared with the strong cold island area, while the leaf vein diameter showed a decreasing trend in the strong heat island area compared with strong cold island area. (2) The vein density, vein diameter, and stomatal length of coriaceous leaves showed an increasing trend in the strong heat island area compared with strong cold island area, while the stomatal density, maximum stomatal conductivity, and upper epidermal thickness showed a decreasing trend in the strong heat island area compared with strong cold island area. (3) Different leaf textures showed varied water related correlations, but both showed a positive correlation between stomatal density and maximum stomatal conductance (p < 0.05). The two types of leaf textures adapted to urban heat island stress by adjusting the different relationships between water related traits.

Conclusion Urban heat islands significantly affect the water related traits of tree leaves, and different textures of leaves adopt different adaptation strategies to the urban heat island environment. Chartaceous leaves adopt a strategy of increasing water supply, improving transpiration, and helping plants cool down. The coriaceous leaves adopt a strategy of increasing water transportation and reducing transpiration water dissipation. There is a phenomenon of co-evolution between the leaf veins and stomata of two tree species with different leaf textures. For urban parks with high heat island intensity, high-temperature resistant tree species should be selected based on indicators such as water correlation, and measures such as increasing irrigation and artificial cooling should be taken during the high-temperature season.