Green roofs can improve ecosystem services in cities; however, this depends on appropriate plant selection. For stormwater management, plants should have high water use to maximize retention and also survive dry periods. Plants adapted to wetter habitats develop “fast” traits for growth, whereas plants from drier habitats develop “slow” traits to conserve water use and survive drought. Therefore, we hypothesized that (1) plants with fast traits would have greater water use, (2) plants with slow traits would have greater drought tolerance, (3) fast-slow traits would be consistent across the plant, and (4) fast plants with greater water use could avoid drought stress. We evaluated 14 green roof species in a glasshouse experiment under well-watered (WW) and water-deficit (WD) conditions to determine relationships between fast-slow traits, water use, and drought resistance. Traits measured were shoot dry mass, specific leaf area (SLA), root mass fraction (RMF), and specific root length (SRL). Daily evapotranspiration per shoot dry mass was used to describe water use. Drought resistance was represented by (1) days to stomatal closure; (2) cumulative ET before stomatal closure; and (3) degree of iso-anisohydry (difference between midday leaf water potential (Ψ_MD) of WW and WD plants; ΔΨ_MD). Plants with greater water use had fast aboveground traits (greater shoot biomass and SLA). Plants with slow traits had greater drought tolerance as plants with lower shoot dry mass closed their stomata later under WD, and plants with greater root allocation were more anisohydric. Fast-slow traits were not consistent across the plant. Although SLA and SRL were positively related, SRL was not related to water use or drought resistance. Shoot dry mass was inversely related to SLA and had a stronger influence on stomatal closure. Though plants with greater water use under well-watered conditions closed their stomates earlier to avoid drought stress, they were not more isohydric (smaller ∆Ψ_MD) and did not necessarily use more water under WD. Fast aboveground traits can be used to select green roof plants with high water use that avoid drought stress to optimize rainfall retention without jeopardizing drought survival. This will facilitate rapid plant selection using trait information from online databases.

中文翻译：

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快速植物具有用水和干旱策略来平衡绿色屋顶上的降雨保留和干旱生存

绿色屋顶可以改善城市的生态系统服务；然而，这取决于适当的植物选择。对于雨水管理，植物应该有高用水量，以最大限度地保留并在干旱时期生存。适应潮湿栖息地的植物会发展出“快速”的生长特征，而来自干燥栖息地的植物会发展出“缓慢”的性状以节约用水和抵御干旱。因此，我们假设（1）具有快速性状的植物会使用更多的水，（2）具有慢速性状的植物将具有更高的耐旱性，（3）快慢性状在整个植物中是一致的，以及（4）快速用水量更大的植物可以避免干旱胁迫。我们在浇水充足 (WW) 和缺水 (WD) 条件下的温室实验中评估了 14 种绿色屋顶物种，以确定快慢特征、用水、和抗旱性。测量的性状是茎干质量、比叶面积 (SLA)、根质量分数 (RMF) 和比根长 (SRL)。每芽干质量的每日蒸发量用于描述用水量。(1) 气孔关闭天数表示抗旱性；(2) 气孔关闭前累积ET；(3) 等水的程度（正午叶水势差（Ψ_MD ) WW 和 WD 植物；ΔΨ _MD )。用水量更大的植物具有快速的地上特征（更大的枝条生物量和 SLA）。具有缓慢性状的植物具有更高的耐旱性，因为在 WD 下，茎干质量较低的植物稍后会关闭它们的气孔，而具有较大根分配的植物则更不等水。快慢特征在整个植物中并不一致。尽管 SLA 和 SRL 呈正相关，但 SRL 与用水或抗旱性无关。茎干质量与 SLA 呈负相关，对气孔闭合的影响更大。尽管在水分充足的条件下用水量更大的植物会更早地关闭气孔以避免干旱胁迫，但它们的等水性并不更高（更小的 ∆Ψ _MD) 并且不一定在 WD 下使用更多的水。快速地上特征可用于选择具有高用水量的绿色屋顶植物，以避免干旱胁迫，以优化降雨保留而不危及干旱生存。这将有助于使用来自在线数据库的性状信息进行快速植物选择。