The provisioning of critical ecosystem services to cities of the eastern United States depends on the health and physiological function of trees in urban areas. Although we know that the urban environment may be stressful for trees planted in highly developed areas, it is not clear that trees in urban forest patches experience the same stressful environmental impacts. In this study, we examine chlorophyll fluorescence parameters, leaf traits, foliar nutrients, and stable isotope signatures of urban forest patch trees compared to trees growing at reference forest sites, in order to characterize physiological response of these native tree species to the urban environment of three major cities arranged along a latitudinal gradient (New York, NY; Philadelphia, PA; Baltimore, MD). Overall, white oaks (Quercus alba L.) show more differences in chlorophyll fluorescence parameters and leaf traits by city and site type (urban vs. reference) than red maples (Acer rubrum L.). The exceptions were 𝛿¹³C and 𝛿¹⁵N, which did not vary in white oak foliage but were significantly depleted (𝛿¹³C) and enriched (𝛿¹⁵N) in urban red maple foliage. Across all sites, red maples had higher thermal tolerance of photosynthesis (T_crit) than white oaks, suggesting a greater ability to withstand temperature stress from the urban heat island effect and climate change. However, the highest average values of T_crit were found in the Baltimore urban white oaks, suggesting that species suitability and response to the urban environment varies across a latitudinal gradient. Stomatal pore index (SPI) showed inter-specific differences, with red maple SPI being higher in urban trees, while white oak SPI was lower in urban trees. These results demonstrate that differences in native tree physiology occur between urban and reference forest patches, but they are site- and species-specific. Data on local site characteristics and tree species performance over time remain necessary to gain insight about urban woodland ecosystem function.

中文翻译：

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城市森林斑块中白橡树和红枫树的叶绿素荧光参数，叶性状和叶化学

向美国东部城市提供关键的生态系统服务取决于城市地区树木的健康和生理功能。尽管我们知道城市环境可能会对高度发达地区种植的树木造成压力，但尚不清楚城市森林斑块中的树木会遭受同样的压力环境影响。在这项研究中，我们检查了与参考森林站点上生长的树木相比，城市森林斑块树的叶绿素荧光参数，叶性状，叶面养分和稳定的同位素特征，以表征这些原生树种对城市环境的生理反应。三个主要城市沿纬度方向排列（纽约，纽约；宾夕法尼亚州，费城；马里兰州巴尔的摩）。总体而言，白橡树（Quercus albaL.）与红枫树（Acer rubrum L.）相比，按城市和地点类型（城市与参考）显示的叶绿素荧光参数和叶片性状差异更大。C ¹³ C和𝛿 ¹⁵ N例外，在白橡树叶中没有变化，但在城市红枫叶中显着耗尽（𝛿 ¹³ C）并富集（𝛿 ¹⁵ N）。在所有地点，红枫树的光合作用（T _crit）耐热性均高于白橡树，这表明其承受城市热岛效应和气候变化带来的温度胁迫的能力更高。但是，T _crit的最高平均值在巴尔的摩市区的白橡树中发现了这种植物，这表明物种的适应性和对城市环境的响应在整个纬度梯度上变化。气孔孔隙度指数（SPI）表现出种间差异，城市树木中的红枫SPI较高，而城市树木中的白橡树SPI较低。这些结果表明，城市林和参考林之间的原生树生理差异，但它们是特定于地点和物种的。为了获得有关城市林地生态系统功能的洞察力，有关随时间变化的本地遗址特征和树种性能的数据仍然很有必要。