Grazers and Phytoplankton Growth in the Oceans: an Experimental and Evolutionary Perspective
Grazers and Phytoplankton Growth in the Oceans: an Experimental and Evolutionary Perspective
复制标题
海洋中的食草动物和浮游植物的生长：实验和进化的视角
作者：
S. Ratti;A. Knoll;M. Giordano
负责大陆架初级生产的浮游植物的分类组成在地球历史上发生了周期性的变化。地质相关性表明，浮游植物组成的主要变化在时间上与放牧和海水化学的变化相对应。验证由这些相关性产生的假设需要实验，因此我们进行了一系列实验，其中选定的浮游植物物种在不同的处理方法中生长，这些处理与食草动物的存在与否以及海水化学有关。两种原生生物(Eplotes sp.)而小节肢动物(Acartia Tonsa)捕食者改变了绿藻Tetraselmis suecica、硅藻Thalassiosira weissflgii和蓝藻聚球藻的生长动力学和生化组成，提高了真核藻的比生长速度和适口性，而降低或保持了蓝藻的这两个参数。聚球藻(特别是聚球藻)和海链球菌产生的毒素对桡足类动物有效，但纤毛虫的生长没有受到影响。阿卡蒂亚诱导硅藻中的硅细胞配额增加4-6倍，而游离藻则没有类似的作用。真核藻和蓝藻对纤毛虫放牧的不同生长反应可能有助于解释真核噬原生生物的明显同龄辐射和真核生物作为新元古代海洋初级生产者的生态重要性的上升。实验结果表明，浮游植物对后期辐射的响应具有支系特异性，包括生长动态、毒素合成、囊化和硅藻对硅吸收的增强。
The taxonomic composition of phytoplankton responsible for primary production on continental shelves has changed episodically through Earth history. Geological correlations suggest that major changes in phytoplankton composition correspond in time to changes in grazing and seawater chemistry. Testing hypotheses that arise from these correlations requires experimentation, and so we carried out a series of experiments in which selected phytoplankton species were grown in treatments that differed with respect to the presence or absence of grazers as well as seawater chemistry. Both protistan (Euplotes sp.) and microarthropod (Acartia tonsa) grazers changed the growth dynamics and biochemical composition of the green alga Tetraselmis suecica, the diatom Thalassiosira weissflogii, and the cyanobacterium Synechococcus sp., increasing the specific growth rate and palatability of the eukaryotic algae, while decreasing or leaving unchanged both parameters in the cyanobacteria. Synechococcus (especially) and Thalassiosira produced toxins effective against the copepod, but ciliate growth was unaffected. Acartia induced a 4-6 fold increase of Si cell quota in the diatom, but Euplotes had no similar effect. The differential growth responses of the eukaryotic algae and cyanobacteria to ciliate grazing may help to explain the apparently coeval radiation of eukaryophagic protists and rise of eukaryotes to ecological prominence as primary producers in Neoproterozoic oceans. The experimental results suggest that phytoplankton responses to the later radiation of microarthropod grazers were clade-specific, and included changes in growth dynamics, toxin synthesis, encystment, and (in diatoms) enhanced Si uptake.