Contrasting heat tolerance of evergreen and deciduous urban woody species during heat waves

The increasing frequency and intensity of heat waves caused significant damages to urban woody species, and the different leaf structures between evergreen and deciduous species may be closely related to leaf heat tolerance. However, whether the different leaf structural traits of evergreen and deciduous plants contribute to their different responses under heat waves is still unclear. During the record‐breaking and long‐lasting 2022 summer heat waves in China, we investigated the relationships between leaf thermal indices and leaf structural traits of 36 urban woody species in four cities along the Yangtze River. We found that all the four thermal indices were significantly but weakly related with leaf damage status. The critical temperature that causes the initial 15% damage to photosystem II (Tcrit) may serve as a sensitive measure of heat tolerance. Evergreen species suffered less leaf damage during the heat waves and exhibited higher leaf heat tolerance, thicker leaves than deciduous species. Tcrit was significantly correlated with leaf mass per area, leaf thickness and thickness of spongy tissue. Synthesis. Urban woody species with higher Tcrit, leaf mass per area and leaf thickness tend to be more tolerant to heat stress. This study provides insights for predicting leaf heat tolerance of urban woody plants in subtropical China and their physiological and ecological responses to severe heat waves. Read the free Plain Language Summary for this article on the Journal blog. 摘要 热浪频率和强度的不断增加对城市木本植物造成了显著损伤，常绿和落叶植物叶片结构性状的差异可能与叶片耐热性密切相关。然而，目前尚不明确常绿和落叶植物叶片结构性状的差异是否会导致它们对热胁迫的不同响应。 在2022年夏季中国多地发生破记录的热浪事件期间，本研究以长江沿岸4个城市的36种园林树种为研究对象，分析了一系列叶片耐热性指标与叶片结构性状的关系。 研究结果表明叶片受损率与叶片耐热性指标均存在显著的负相关关系，其中叶片光系统II损伤15%时的温度(Tcrit)可作为衡量叶片耐热性的关键指标。与落叶种相比，常绿种具有更厚的叶片，在热浪下的叶片损伤率更低，表现出更高的叶片耐热性。Tcrit与叶片比叶重、叶片厚度和海绵组织厚度存在显著正相关关系。 具有较高Tcrit、叶片比叶重和叶片厚度的城市木本植物对热胁迫的耐受性更强。本研究为预测中国亚热带城市木本植物的叶片耐热性及其对热浪的生理生态响应提供了新见解。 Read the free Plain Language Summary for this article on the Journal blog.