This study examined the acclimation to temperature of two globally invasive species Iris pseudacorus and Lythrum salicaria, which share the same habitat type but differ in morphology. Iris pseudacorus has long vertical leaves, allowing light penetration through the canopy, while L. salicaria has stems with small horizontal leaves, creating significant self-shading. We aimed to build a physiological understanding of how these two species respond to different growth temperatures with regard to growth and gas exchange-related traits over the canopy. Growth and gas exchange-related traits in response to low (15 °C) and high (25 °C) growth temperature regimes were compared. Plants were grown in growth chambers, and light response curves were measured with infrared gas analysers after 23–33 days at three leaf positions on each plant, following the vertical light gradient through the canopy. After 37 days of growth, above-ground biomass, photosynthetic pigments and leaf N concentration were determined. The maximum photosynthesis rate was lower in lower leaf positions but did not differ significantly between temperatures. Iris pseudacorus photosynthesis decreased with decreasing leaf position, more so than L. salicaria. This was explained by decreasing N and chlorophyll concentrations towards the leaf base in I. pseudacorus, while pigment concentrations increased towards the lower canopy in L. salicaria. Biomass, shoot height and specific leaf area increased with temperature, more so in I. pseudacorus than in L. salicaria. Light response curves revealed that L. salicaria had a higher degree of shade acclimation than I. pseudacorus, probably due to self-shading in L. salicaria. High temperature decreased C assimilation at the bottom of the canopy in L. salicaria, while C assimilation in I. pseudacorus was less affected by temperature. As vegetative growth and flowering was stimulated by temperature, the invasive potential of these species is predicted to increase under global warming.

中文翻译：

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叶片和整株植物的结构决定了在不同温度条件下种植的侵入性植物冠层通过垂直光梯度产生的碳同化作用。

这项研究检查了两个全球入侵物种鸢尾鸢尾和千屈菜的温度适应性，它们具有相同的生境类型但形态不同。鸢尾鸢尾具有较长的垂直叶片，可以使光线穿过树冠，而水杨茎具水平小叶，形成明显的自阴影。我们的目标是建立关于这两种物种对冠层生长和与气体交换相关的性状如何响应不同生长温度的生理理解。比较了在低（15°C）和高（25°C）生长温度条件下生长和与气体交换相关的性状。使植物在生长室中生长，并在23-33天后，按照垂直光梯度穿过树冠，在每个植物的三个叶片位置上用红外气体分析仪测量光响应曲线。生长37天后，测定了地上生物量，光合色素和叶片氮浓度。在较低的叶片位置，最大光合作用速率较低，但温度之间没有显着差异。菖蒲光合作用随叶位置的，比下降L.屈菜。这可以通过减少假单胞菌向叶基部的氮和叶绿素浓度来解释，而向唾液酸乳杆菌的下部冠层中的色素浓度则增加。生物量，枝条高度和比叶面积随温度增加而增加，假I. pseudacorus比L. salicaria更大。光响应曲线表明，L.屈有较高程度的遮阳驯化的比黄菖蒲中，可能是由于自遮蔽L.屈。高温降低了水杨柳冠层底部的C同化，而P.udacorus的C同化受温度的影响较小。随着温度刺激营养生长和开花，预计这些物种的入侵潜力在全球变暖下会增加。