Forest Ecology, Department of Terrestrial Ecosystems, ETH Zürich, Universitätsstr.16, 8092 Zurich, Switzerland.
Planta. 2011 Jun;233(6):1087-96. doi: 10.1007/s00425-011-1363-6. Epub 2011 Feb 4.
Ivy (Hedera helix) is the most important liana in temperate European forests. We studied water relations of adult ivy in a natural, 35 m tall mixed deciduous forest in Switzerland using a construction crane to access the canopy. Predawn leaf water potential at the top of climbing ivy ranged from -0.4 to -0.6 MPa, daily minima ranged from -1.3 to -1.7 MPa. Leaf water potentials as well as relative sap flow were held surprisingly constant throughout different weather conditions, suggesting a tendency to isohydric behaviour. Maximum stomatal conductance was 200 mmol m⁻² s⁻¹. The use of a potometer experiment allowed us to measure absolute transpiration rates integrated over a whole plant of 0.23 mmol m⁻² s⁻¹. Nightly sap flow of ivy during warm, dry nights accounted for up to 20% of the seasonal maximum. Maximum sap flow rates were reached at ca. 0.5 kPa vpd. On the other hand, the host trees showed a less conservative stomatal regulation, maximum sap flow rates were reached at vpd values of ca. 1 kPa. Sap flow rates of ivy decreased by ca. 20% in spring after bud break of trees, suggesting that ivy profits strongly from warm sunny days in early spring before budbreak of the host trees and from mild winter days. This species may benefit from rising winter temperatures in Europe and thus become a stronger competitor against its host trees.
常春藤（Hedera helix）是温带欧洲森林中最重要的藤本植物。我们使用建筑起重机进入树冠，在瑞士的一个天然、35 米高的混合落叶林中研究成年常春藤的水分关系。攀爬常春藤顶部的黎明前叶片水势范围为-0.4 至-0.6 MPa，日最小值范围为-1.3 至-1.7 MPa。叶片水势以及相对液流在不同天气条件下保持惊人的稳定，表明具有等水行为的趋势。最大气孔导度为 200 mmol m⁻² s⁻¹。使用蒸腾计实验，我们可以测量整个植物的绝对蒸腾速率，集成值为 0.23 mmol m⁻² s⁻¹。在温暖干燥的夜晚，常春藤的夜间液流可占季节最大值的 20%。最大液流速率在约 0.5 kPa vpd 时达到。另一方面，宿主树木表现出不那么保守的气孔调节，最大液流速率在约 1 kPa vpd 时达到。在树木萌芽后，春季常春藤的液流速率下降约 20%，这表明常春藤在树木萌芽前的早春温暖晴天以及温和的冬季受益良多。这种物种可能受益于欧洲冬季气温上升，因此成为其宿主树木的更强大竞争者。
