Table_2_The Ecophysiological Response of Two Invasive Submerged Plants to Light and Nitrogen.doc

Two submerged Elodea species have small differences in their ecophysiological responses when exposed to individual environmental factors. However, field observations showed that under eutrophic conditions with low light availability, Elodea canadensis could be displaced by Elodea nuttallii. Here we investigated the combined effect of environmental factors on the ecophysiological response of the two species in order to explain the differences in their invasion successes. We cultivated the plants in aquaria containing five different nitrogen (N) concentrations and incubated at five different light intensities. For both species increasing nitrogen concentrations resulted in increased relative growth rate, chlorophyll concentration, and actual photochemical efficiency of photosystem II (ΦPSII), however, they produced less roots. Lowering light intensity resulted in a lower relative growth rate, root production, and nutrient removal. In contrast, chlorophyll concentration in the leaves, and ΦPSII increased. The main difference between the two Elodea species was that the light compensation point (Ic) and weight loss in the dark were significantly higher and photochemical efficiency and chlorophyll concentration were significantly lower for E. canadensis than for E. nuttallii, indicating that the latter can survive under much more shady and hypertrophic conditions. The change in nitrogen concentration of the media and in tissue concentration of the plants indicated that E. nuttallii has a higher nitrogen removal capacity. The ecophysiological differences between the two species can be an explanation for invasion success of E. nuttallii over E. canadensis and thus may explain why the latter is replaced by the first.

两种沉水植物物种在遭受单一环境因素影响时，其生态生理响应存在细微差异。然而，实地观察表明，在富营养化条件下且光照不足的情况下，加拿大水葫芦（Elodea canadensis）可能被美洲水葫芦（Elodea nuttallii）所取代。本研究旨在探究环境因素对两种物种生态生理响应的联合作用，以阐释它们在入侵成功中的差异。我们分别在含有五种不同氮浓度（N）的水族箱中培养植物，并在五种不同的光照强度下进行孵化。对于两种物种而言，氮浓度的增加均导致相对生长率、叶绿素浓度和光系统II的实际光化学效率（ΦPSII）的提高，然而，它们的根系生长却相对较少。降低光照强度则导致相对生长率、根系生长和养分去除率下降，与此同时，叶片中的叶绿素浓度和ΦPSII却有所增加。两种Elodea物种之间的主要差异在于，与美洲水葫芦相比，加拿大水葫芦的光补偿点（Ic）和黑暗中的重量损失显著更高，而光化学效率和叶绿素浓度则显著更低，这表明后者能够在更为阴暗和富营养的环境中生存。培养基中氮浓度的变化以及植物组织中的氮浓度变化表明，美洲水葫芦具有更高的氮去除能力。两种物种间的生态生理差异可能是美洲水葫芦相对于加拿大水葫芦的入侵成功提供了一种解释，从而可能阐明为何后者被前者所取代。