浒苔(Ulva prolifera)漂浮生态型的分枝表型及其可塑性

黄海绿潮由浒苔漂浮生态型主导，普遍认为其具有高度分枝的表型特征，但始终缺乏形态学的量化表征。本研究针对浒苔的分枝表型，通过广泛采集漂浮生态型与定生群体样本，使用最高分枝级数和一级分枝密集度两个形态学指标进行了量化表征，结果表明，定生浒苔普遍仅有一级分枝或无分枝，而漂浮生态型分枝级数最高可达五级，其一级分枝密集度是定生浒苔的5.8倍，说明漂浮生态型的分枝程度显著高于定生浒苔。另外，无论自然条件还是人工培养条件下，发现漂浮生态型分枝表型的可塑性也明显强于定生群体。上述结果提示，高度分枝表型是漂浮生态型重要的漂浮适应性特征；而分枝表型的强可塑性，可能有助于其适应漂浮过程中多变的海洋环境。上述结论可为后续深入研究提供形态学量化指标和重要理论依据。

Branching phenotype and plasticity in floating ecotype of Ulva prolifera (Ulvophyceae, Chlorophyta)

The floating ecotype of Ulva prolifera is known to dominate the green tide in the Yellow Sea. It is generally considered to have highly branched phenotypic characteristics, but always lacks a quantitative morphological characterization. This study aims to quantitatively characterize the branching phenotypes of U. prolifera by extensively sampling both the floating ecotypes and attached populations, and using two morphological indexes (the top branching order and the intensity of primary branches). The results showed that the top branching order might reach up to five levels in the floating ecotype, whereas the intensity of primary branches was found to be 5.8 times higher than that of the attached populations, which are usually unbranched. These results indicate a significant difference in the branching phenotypes of floating ecotypes and attached populations. In addition, the plasticity of branching phenotypes was also much stronger in the floating ecotype than the attached populations under different type of conditions. These results suggest that the highly branched phenotype is an essential adaptive feature of the floating ecotypes, and the strong plasticity of the branched phenotype may help them in adapting to the changeable marine environment. These conclusions can provide a quantitative morphological index and an important theoretical basis for further studies.