Traits coordination at leaf and branch level in response to the urban environment.

The response of urban trees to the environment is the key content to explain the functional toughness of urban green space. However, how urban greening trees adapt to the dry and hot environment of the city remains unclear due to the single index and the limitations of the research area. We selected four representative cities in northern China with different regional dryness and measured 18 economic, hydraulic and anatomical traits of the common greening tree species (Fraxinus chinensi s Roxb). The results show that there was generally a significant divergence in plant functional traits across urban dryness, and the traits have strong plasticity. As urban dryness increases, the number of leaf veins closed loops increases, forming a more complete network system of veins. While a significant decrease in the vessel vulnerability index further indicates the increased drought tolerance of urban trees to resist dry and hot environments. The increase of dryness leads to the decrease of vessel hydraulic diameter and area. The reduction in the vessel vulnerability index indicates an increase in the drought resistance of the twigs, which may be related to the input and distribution of resources in the branches and leaves. There was a strong correlation between plant economic-anatomical-hydrological traits. Under the stress of a dry urban environment, plants prefer to invest resources in the water sparing capacity of the stem, as well as in the construction of defence structures and nutrient storage capacity of the leaves. [Display omitted] • Environmental variable (urban dryness) was significantly correlated with economic, hydraulic and anatomical traits. • There was more positive correlation (cooperative development) between vessel traits and vein traits, while there was more negative correlation (trade-off) between stomatal traits and vein traits. • Urban dryness promotes the formation of a more complete vein network system. • Under the stress of urban arid environment, urban trees adopt the strategy of sacrificing the supporting function of trunk to ensure the safe transportation of water. [ABSTRACT FROM AUTHOR]