There is much uncertainty in how climate change will impact the performance of urban trees. Climate niche modelling predicts that many urban tree species may become unsuitable in future climates, but this has rarely been tested in cities. Broad planting of diverse tree species in different cities provides the opportunity to test climate niche predictions. Here we investigated if the climate of origin of 14 urban tree species influenced tree growth, trait expression, and phenotypic plasticity. We determined climate niche limits for all species and measured canopy growth rates of individual trees from 2013 to 2021 in the two largest Australian cities: subtropical Sydney, and temperate Melbourne. Six functional traits including leaf water potential at turgor loss point (TLP), wood density (WD), leaf dry matter content (LDMC), specific leaf area (SLA), carbon isotope composition (δC) and Huber value (HV) were measured in both cities. Trees planted outside their climate niche limits had lower growth than trees planted inside their climate niche in the temperate but not subtropical city. Species with lower MAP of origin (i.e., drier) had faster canopy growth in both cities. Species with low MAP and high heat moisture index (HMI) at their origin had more negative TLP and greater WD, indicating species from drier environments maintain their high drought tolerance in cities. Trees planted in drier Melbourne had more negative TLP, higher WD and higher LDMC than in Sydney, demonstrating phenotypic plasticity in urban trees. Wetter origin species showed greater phenotypic plasticity in TLP, WD and δC. Canopy RGR was negatively related with δC reflecting a strong impact of stomatal behaviour on urban tree growth. Our study provides limited support that species climate niche limits reliably predict urban tree growth, so we caution against solely using climate niche matching and advocate for inclusion of functional traits when selecting urban tree species.

中文翻译：

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物种气候生态位能否预测城市树木的冠层生长、功能特征和表型可塑性？


气候变化将如何影响城市树木的性能存在很大的不确定性。气候生态位模型预测，许多城市树种可能会变得不适合未来的气候，但这很少在城市中得到测试。在不同城市广泛种植不同树种为测试气候生态位预测提供了机会。在这里，我们调查了 14 种城市树种的起源气候是否影响树木的生长、性状表达和表型可塑性。我们确定了所有物种的气候生态位限制，并测量了 2013 年至 2021 年澳大利亚两个最大城市：亚热带悉尼和温带墨尔本的单株树木的树冠生长率。测定了叶片膨压损失点水势（TLP）、木材密度（WD）、叶片干物质含量（LDMC）、比叶面积（SLA）、碳同位素组成（δ13C）和Huber值（HV）等6个功能性状在两个城市。在温带而非亚热带城市，在其气候生态位限制之外种植的树木的生长速度低于在其气候生态位内种植的树木。 MAP 来源较低（即较干燥）的物种在两个城市的树冠生长较快。原产地具有低 MAP 和高热湿指数 (HMI) 的物种具有更高的负 TLP 和更大的 WD，这表明来自干燥环境的物种在城市中保持了高耐旱性。与悉尼相比，在干燥的墨尔本种植的树木具有更多的负 TLP、更高的 WD 和更高的 LDMC，这表明城市树木的表型可塑性。较湿润的起源物种在 TLP、WD 和 δ13C 方面表现出更大的表型可塑性。冠层 RGR 与 δ13C 呈负相关，反映出气孔行为对城市树木生长的强烈影响。 我们的研究提供了有限的支持，即物种气候生态位限制能够可靠地预测城市树木的生长，因此我们警告不要仅使用气候生态位匹配，并主张在选择城市树种时纳入功能性状。