Allelopathy, a type of interference competition involving exuded chemicals, has been documented for several types of organisms including terrestrial plants, aquatic macrophytes, microbes, and planktonic algae. However, due to the dynamic nature of the aquatic environment it is unclear whether allelopathy is an evolutionarily stable competition mechanism in such a setting. In this research, we consider a cosmopolitan harmful algae species, Prymnesium parvum, for which multiple ecological roles of its produced deleterious chemicals have been suggested, including broadcast allelopathy (chemicals produced and exuded) and micropredation via cell–cell interactions (chemicals produced and held within the cell). To further investigate the ecological role of the deleterious chemicals, bioassays (with phytoplankton and zooplankton target organisms) were conducted using various fractions of a P. parvum culture grown under balanced N:P stoichiometry or imbalanced, P‐reduced stoichiometry. In addition, time‐series counts were generated with cell density enumerations and observations of behavior of a mixed species culture at intervals over a 24‐h period. Our results suggest that the apparent ecological role of the chemicals in a relatively high‐density population shifts depending on system stoichiometry in regard to nitrogen and phosphorus. We show that under balanced N:P conditions, deleterious chemical production is low and cell contact mediates mortality of prey. Differently, under imbalanced, P‐reduced conditions chemical effect is high and mass mortality occurs independent of cell contact. Thus, imbalanced N:P ratios shift the apparent ecological role of the deleterious chemicals from one of micropredation to one of broadcast allelopathy. These differences likely influence bloom dynamics and result in different ecological outcomes for systems affected by blooms. Further, we suggest that these differences indicate the importance of predatory mixotrophic feeding in the evolutionary maintenance of deleterious chemical production and the occurrence of allelopathic effects as a byproduct.

中文翻译：

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化感作用和微捕食范例与系统化学计量调和

化感病是一种涉及竞争性竞争的化学物质，涉及到渗出的化学物质，已针对多种生物进行了记录，包括陆生植物，水生植物，微生物和浮游藻类。然而，由于水生环境的动态性质，目前尚不清楚在这种情况下化感作用是否为进化上稳定的竞争机制。在这项研究中，我们考虑了一种国际性的有害藻类，Prymnesium parvum对此，已经提出了其产生的有害化学物质的多种生态作用，包括广播化感作用（产生和渗出的化学物质）和通过细胞-细胞相互作用进行微捕食（产生并保留在细胞内的化学物质）。为了进一步研究有害化学物质的生态作用，使用了小球藻的各种成分进行了生物测定（对浮游植物和浮游动物为目标生物）。在平衡的N：P化学计量比或不平衡的P减少的化学计量比下生长的培养物。此外，时间序列计数是通过细胞密度枚举和混合物种培养物在24小时内的间隔观察行为而产生的。我们的结果表明，化学物质在较高密度种群中的明显生态作用根据氮和磷的系统化学计量而变化。我们表明，在平衡的N：P条件下，有害化学物质的产生较低，并且细胞接触介导了猎物的死亡。不同的是，在失衡的情况下，P减少的条件下，化学作用很高，并且发生的质量死亡与细胞接触无关。因此，N：P比例失衡将有害化学物质的表观生态作用从微量捕食之一转移到广播化感病之一。这些差异可能影响水华动态，并导致受水华影响的系统具有不同的生态结果。此外，我们建议这些差异表明掠食性混合营养的进食在有害化学生产的进化维持和化感作用作为副产物的发生中的重要性。