Department of Biology and Environmental Sciences, Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University, 39231 Kalmar, Sweden.
University of Maryland Center for Environmental Science, Horn Point Laboratory, P.O. Box 775, Cambridge, MD 21613, USA.
Harmful Algae. 2016 May;55:1-12. doi: 10.1016/j.hal.2016.01.002. Epub 2016 Feb 8.
Mixotrophy is found in almost all classes of phytoplankton in a wide range of aquatic habitats ranging from oligotrophic to eutrophic marine and freshwater systems. Few studies have addressed how the nutritional status of the predator and/or the prey affects mixotrophic metabolism despite the realization that mixotrophy is important ecologically. Laboratory experiments were conducted to examine changes in growth rates and physiological states of the toxic haptophyte Prymnesium parvum when fed Rhodomonas salina of varying nutritional status. Haemolytic activity of P. parvum and prey mortality of R. salina were also measured. P. parvum cultures grown to be comparatively low in nitrogen (low-N), phosphorus (low-P) or low in both nutrients (low-NP) were mixed with low-NP, low-N, and low-P R. salina in all possible combinations, i.e., a 3×3 factorial design. N deficiency was obtained in the low-N cultures, while true P deficiency may not have been obtained in the low-P cultures. Mortality rates of R. salina (both due to ingestion and/or cell rupture as a function of grazing or toxic effects) were higher when R. salina cells were low-P, N-rich, regardless of the nutritional state of P. parvum. Mortality rates were, however, directly related to the initial prey:predator cell ratios. On the other hand, growth of the predator was a function of nutritional status and a significant positive correlation was observed between growth rates of P. parvum and cell-specific depletion rates of N, whereas no such relationship was found between P. parvum growth rates and depletion rates of P. In addition, the greatest changes in chlorophyll content and stoichiometric ratios of P. parvum were observed in high N:P conditions. Therefore, P. parvum may show enhanced success under conditions of higher inorganic N:P, which are likely favored in the future due to increases in eutrophication and altered nutrient stoichiometry driven by anthropogenic nutrient loads that are increasingly enriched in N relative to P.
混养在从贫营养到富营养的海洋和淡水系统中的几乎所有浮游植物类群中都有发现。尽管人们已经认识到混养在生态上很重要，但很少有研究探讨捕食者和/或猎物的营养状况如何影响混养代谢。进行了实验室实验，以检查营养状况不同的 Rhodomonas salina 喂养时，有毒甲藻 P. parvum 的生长速率和生理状态的变化。还测量了 P. parvum 的溶血活性和 R. salina 的猎物死亡率。将比较低氮（低-N）、低磷（低-P）或两者都低（低-NP）的 P. parvum 培养物与低-NP、低-N 和低-P 的 R. salina 混合，以所有可能的组合，即 3×3 析因设计。低-N 培养物中存在氮缺乏，而低-P 培养物中可能未获得真正的磷缺乏。当 R. salina 细胞低-P、富 N 时，无论 P. parvum 的营养状态如何，R. salina 的死亡率（由于摄食和/或细胞破裂作为放牧或毒性效应的函数）都更高。然而，死亡率与初始猎物：捕食者细胞比直接相关。另一方面，捕食者的生长是营养状况的函数，并且观察到 P. parvum 的生长速率与 N 的细胞特异性消耗率之间存在显著正相关，而在 P. parvum 的生长速率与 P 的消耗率之间未发现这种关系。此外，P. parvum 的叶绿素含量和化学计量比的最大变化发生在高 N:P 条件下。因此，P. parvum 在较高的无机 N:P 条件下可能表现出更高的成功，由于富营养化的增加和人为养分负荷驱动的养分化学计量的改变，未来可能会出现这种情况，因为与 P 相比，N 相对富集的人为养分负荷越来越多。
