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首页> 外文期刊>Open Journal of Ecology >Seasonal patterns of light availability and light use of broadleaf evergreens in a deciduous forest understory: Potential mechanisms for expansion
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Seasonal patterns of light availability and light use of broadleaf evergreens in a deciduous forest understory: Potential mechanisms for expansion

机译：落叶林下层林地常绿阔叶树的光能利用率和光利用率的季节性模式：潜在的扩展机制

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In recent years, expansion of native and exotic evergreen shrubs into forest understories has been documented worldwide. Dense shrub thickets may interfere with tree establishment, suppress herbaceous cover, and contribute substantially to total standing crop of leaf biomass. Expansion may occur because evergreen shrubs exploit seasonal variations in irradiance and temperature that are characteristic of temperate understory environments. We quantified leaf-level light environment and photosynthetic activity of three sympatric broadleaf evergreens (Ilex opaca, Kalmia latifolia, and Myrica cerifera) in a deciduous forest understory in Charles City County,Virginia,USAin order to understand seasonal intra- and interspecific ranges of broadleaf evergreen physiology. Two species (K. latifolia and M. cerifera) represent a diverse taxonomic range within broadleaf evergreens, and often form expansive thickets. We measured parameters related to canopy structure (e.g., bifurcation ratio, leaf angle) and photosynthetic performance (e.g., electron transport rate or ETR, chlorophyll content), to identify potential mechanisms facilitating expansion. ETR varied both seasonally and among species. In summer, M. cerifera ETR was nearly double that ofI. opaca or K. latifolia. Additionally, leaf temperature enhanced photosynthetic capacity of expansive species. Evergreen species, though capable of fixing carbon throughout the year, often exhibit slow growth rates and low physiological activity. Yet, we observed that the range of evergreen physiological activity may be broader than previously recognized. Furthermore, our results indicate potential for changes in composition and expansion of the evergreen shrub layer by species that exhibit structural and physiological mechanisms advantageous for future rises in temperature.
机译：近年来，世界范围内已有文献记录将原生和外来的常绿灌木扩展到森林底层。茂密的灌木丛可能会干扰树木的生长，抑制草本植物的覆盖，并大大促进叶片生物量的整体稳定。可能会发生膨胀，因为常绿灌木会利用辐照度和温度的季节性变化，这些变化是温带林下环境的特征。我们对美国弗吉尼亚州查尔斯市县落叶林下林中的三种同伴阔叶常绿植物（冬青，欧芹，阔叶红叶和杨梅）的叶级光照环境和光合活性进行了定量分析，以了解阔叶植物的季节内和种间分布常绿生理。阔叶常绿植物中的两个物种（阔叶假单胞菌和cerifera cerifera）代表了不同的生物分类学范围，并且经常形成广阔的灌木丛。我们测量了与冠层结构（例如，分叉比，叶角）和光合性能（例如，电子传输速率或ETR，叶绿素含量）有关的参数，以识别促进扩展的潜在机制。 ETR随季节和物种而变化。夏季，cerifera cerifera ETR几乎是I的两倍。 opaca或K. latifolia。此外，叶片温度增强了膨胀物种的光合能力。常绿树种虽然一年四季都能固定碳，但常表现出缓慢的生长速度和较低的生理活性。然而，我们观察到常绿生理活性的范围可能比以前认识的要广泛。此外，我们的结果表明，具有表现出有利于未来温度升高的结构和生理机制的物种可能会改变常绿灌木层的组成和膨胀。

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