Response And Adaptation Mechanism Of Leaf Functional Traits In Cinnamomum Camphora To Urban Hot And Arid Environment

Urbanization brings many benefits to residents,but it also introduces complex,variable,and heterogeneous environmental conditions for urban plants.The typical climatic features accompanying urbanization,such as urban heat islands and urban dry islands,have become significant factors threatening the survival of urban trees and influencing their ecological functions.Therefore,studying the ecological strategies of urban trees in dry and hot urban environments is crucial for the future management and planning of urban trees.Plant functional traits are essential methods and perspectives to understand plant physiological and ecological strategies,and their responses and adaptations to urban environments are among the research focuses in urban and landscape ecology.Intraspecific variation of plant functional traits can reveal the response and adaptation mechanisms of plants to environmental changes,providing a theoretical basis for intraspecific physiological and ecological strategies.There have been more studies on economic traits related to plant resource acquisition and conservation among urban plants.However,a consensus has yet to be reached on the resource utilization strategies of urban plants.Furthermore,plant‘hard’traits（such as leaf hydraulic conductance,leaf hydraulic vulnerability,leaf drought resistance,etc.）are crucial for understanding plant strategies.However,studies on these plant traits in urban environments are relatively limited.Therefore,gaining insights into the response mechanisms of leaf functional traits in the urban dry and hot environment,especially‘hard’traits,enhances our understanding of plant physiological and ecological strategies for coping with urban environments.In this study,Cinnamomum camphora,a commonly used street tree species in East China,was selected as the research object,and the leaf hydraulic,anatomical,and nutrient functional traits were measured under the background of impermeable pavement and urban-rural gradients so as to explore further the impact of dry and hot urban environment on the physiological and biochemical characteristics of leaves and the mechanism of intraspecific variation and coordination,the main results of the study are as follows:（1）The response of leaf functional traits under pavement environment.The results showed that the water status（soil volumetric water content,air relative humidity）in the street pavement environment was the key factor driving the response of plant leaf economic and hydraulic traits.Cinnamomum camphora adapted to the pavement environment with slow investment return economic strategy（low specific leaf area,high leaf dry weight and leaf thickness）and high hydraulic safety strategy(low P₅₀).（2）The response of leaf functional traits under the urban-rural gradient.The results showed that Cinnamomum camphora adapted to the dry and hot urban environment with quick investment return economic strategy（low LMA and high leaf nitrogen content）and conservative hydraulic strategy(low P₅₀,leaf turgor loss point,leaf hydraulic conductivity).In the urban-rural gradient,there was a trade-off between safety and efficiency in leaf hydraulic traits.（3）In the dry and hot urban environment,there were coordinated intraspecific variations in the leaf hydraulic and economic traits of Cinnamomum camphora,which indicated that the leaf economic and hydraulic traits were coupled to each other in the urban environment.In addition,mesophyll anatomical traits（ratio of spongy tissue thickness to palisade tissue thickness）and stomatal traits（stomata density,stomata length）were the key traits that regulated the hydraulic and economic adaptation strategies of Cinnamomum camphora.（4）Under the two dry and hot urban environments,the leaf hydraulic traits were all mutated towards the conservative strategy characterized by the low leaf turgor loss point and P₅₀.However,the direction of intraspecific leaf economic traits variation was inconsistent.Cinnamomum camphora in the pavement environment adopted a slow investment return strategy with high leaf dry weight and leaf thickness.In contrast,Cinnamomum camphora in the urban-rural gradient adopted a quick investment return strategy with low LMA and high leaf nitrogen content.These results indicated that water and temperature were the main environmental limiting factors in extreme hot and dry environments.At the same time,Cinnamomum camphora may be more affected by other urban environmental factors in milder hot and dry environments.Therefore,future research should encompass a broader range of urban environmental factors,enabling a more comprehensive understanding of how urban trees adapt to the complex urban environment.