Abstract:Frequent extreme high temperature and heat waves seriously threaten the growth and survival of urban plants. The heat resistance of leaves can reflect the tolerance and adaptability of plants to heat stress. Exploring the relationship between leaf heat tolerance and their structural traits in urban garden tree species can reveal the ecological adaptation strategies of urban plants under heat stress, thereby enhancing the predictive ability of their responses and adaptations to high temperatures. This study took 10 common urban garden tree species in Chongqing (3 species of Ficus from Moraceae, 4 species of Magnolia from Magnoliaceae, and 3 species from Rosaceae) as research subjects, comparing their leaf damage rates, heat tolerance, and structural traits during the 2022 heatwave event, and analyzing their different heat adaptation strategies. The results showed that there was a significant negative correlation between leaf damage rate and heat tolerance under natural heatwaves. The leaves of Ficus species from Moraceae had higher heat tolerance, resulting in lower leaf damage rates; while Magnolia species and Rosaceae species had lower heat tolerance, but they might avoid heat stress through adaptation strategies such as changing leaf inclination angles and shedding leaves during heatwaves. Additionally, heat tolerance was significantly negatively correlated with leaf area, upper epidermis thickness, and the ratio of palisade to spongy tissue thickness. These traits can predict leaf heat tolerance relatively well. Therefore, the study of heat adaptation strategies of three typical urban garden woody plants under heatwaves is of great significance for the selection of heat-tolerant tree species in cities and the prediction of damage risks to trees under heat stress.
