Increasing tree species diversity has become a key underpinning for communities to improve resilience of urban and community forests. Increasingly, urban forestry researchers are examining physiological traits to aid in selecting trees for urban sites. Knowledge of physiological responses also has implications for understanding species’ resilience to increased stresses associated with climate change. Here, we compare growth, leaf SPAD chlorophyll index, water relations, and gas exchange of seven genotypes of shade trees planted in two locations in downtown Detroit, MI, USA. Genotypes included Redpointe® maple (Acer rubrum ‘Frank Jr.’), Flashfire® maple (Acer saccharum ‘JFS-Caddo2′), Pacific Sunset® maple (Acer truncatum x platanoides ‘Warrenred’), Emerald City® tulip tree (Liriodendron tulipifera ‘JFS-Oz’), Chanticleer® pear (Pyrus calleryana ‘Glen’s Form’), swamp white oak (Quercus bicolor), and Emerald Sunshine® elm (Ulmus propinqua ‘JFS-Bieberich’). Trees were planted in either Lafayette Plaisance Park (Park), a large urban greenspace, or on the median of St. Aubin Avenue (Median), a nearby major thoroughfare. Tree height growth and leaf SPAD index were higher for trees planted in the Park location than on the Median. However, genotypic variation was larger than the effects of location or the interaction of Genotype × Location for most traits. Across measurement dates, midday leaf water potential was lowest for Pyrus trees and highest for Ulmus and Liriodendron trees. Pyrus and Quercus trees had relatively high rates of net photosynthesis (A) and stomatal conductance (g_s) while Liriodendron, Acer saccharum, and Ulmus trees had low rates of A and g_s. Liriodendron trees closed their stomata rapidly as leaf water potential (Ψ_w) declined (isohydric response), while Pyrus and Quercus trees maintained g_s across a range of leaf Ψ_w (anisohydric response). Liriodendron trees also had the highest relative growth rates, suggesting that drought stress avoidance through isohydry is a viable drought tolerance mechanism in urban trees.

增加树种多样性已成为社区提高城市和社区森林恢复力的关键支撑。越来越多的城市林业研究人员正在研究生理特征，以帮助为城市地点选择树木。了解生理反应也有助于了解物种对与气候变化相关的压力增加的适应力。在这里，我们比较了种植在美国密歇根州底特律市中心两个地点的七种基因型遮荫树的生长、叶片 SPAD 叶绿素指数、水分关系和气体交换。基因型包括 Redpointe® 枫树（Acer rubrum 'Frank Jr.'）、Flashfire® 枫树（Acer saccharum 'JFS-Caddo2'）、Pacific Sunset® 枫树（Acer truncatum x platanoides'Warrenred'）、Emerald City® 郁金香树（Liriodendron tulipifera 'JFS-Oz'）、Chanticleer® 梨（Pyrus calleryana 'Glen's Form'）、沼泽白橡树（Quercus bicolor）和 Emerald Sunshine® 榆树（Ulmus propinqua 'JFS -比伯里希')。在大型城市绿地 Lafayette Plaisance Park (Park) 或附近主要干道 St. Aubin Avenue (Median) 的中间地带种植了树木。种植在公园位置的树木的树高生长和叶片 SPAD 指数高于中位数。然而，对于大多数性状，基因型变异大于位置或基因型×位置相互作用的影响。在整个测量日期中，梨的正午叶水势最低树，最高的是榆树和鹅掌楸树。梨树和栎树的净光合速率( A )和气孔导度( g _s )相对较高，而鹅掌楸、甘蔗枫和榆树的A和g _s速率较低。当叶水势 (Ψ _w ) 下降（等水反应）时，鹅掌楸树迅速关闭气孔，而梨树和栎树在整个叶 Ψ _w范围内保持g _s（异水反应）。鹅掌楸树的相对生长率也最高，表明通过等水性避免干旱胁迫是城市树木的一种可行的耐旱机制。