Foraminifera are unicellular organisms that play an important role in marine organic matter cycles. Some species are able to isolate chloroplasts from their algal food source and incorporate them as kleptoplasts into their own metabolic pathways, a phenomenon known as kleptoplastidy. One species showing this ability is Elphidium excavatum, a common foraminifer in the Kiel Fjord, Germany. The Kiel Fjord is fed by several rivers and thus forms a habitat with strongly fluctuating salinity. Here, we tested the effects of the food source, salinity and light regime on the food uptake (via ¹⁵N and ¹³C algal uptake) in this kleptoplast-bearing foraminifer. In our study E. excavatum was cultured in the lab at three salinity levels (15, 20 and 25) and uptake of C and N from the food source Dunaliella tertiolecta (Chlorophyceae) and Leyanella arenaria (Bacillariophyceae) were measured over time (after 3, 5 and 7 d). The species was very well adapted to the current salinity of the sampling region, as both algal N and C uptake was highest at a salinity of 20. It seems that E. excavatum coped better with lower than with higher salinities. The amount of absorbed C from the green algae D. tertiolecta showed a tendency effect of salinity, peaking at a salinity of 20. Nitrogen uptake was also highest at a salinity of 20 and steadily increased with time. In contrast, C uptake from the diatom L. arenaria was highest at a salinity of 15 and decreased at higher salinities. We found no overall significant differences in C and N uptake from green algae vs. diatoms. Furthermore, the food uptake at a light–dark rhythm of 16:8 h was compared to continuous darkness. Darkness had a negative influence on algal C and N uptake, and this effect increased with incubation time. Starving experiments showed a stimulation of food uptake after 7 d. In summary, it can be concluded that E. excavatum copes well with changes of salinity to a lower level. For changes in light regime, we showed that light reduction caused a decrease of C and N uptake by E. excavatum.

中文翻译：

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盐度，光照和食物来源对底栖有孔虫碳氮吸收的影响

有孔虫是在海洋有机物质循环中起重要作用的单细胞生物。一些物种能够从藻类食物来源中分离出叶绿体，并将它们作为裂殖体并入其自身的代谢途径，这种现象被称为变皱体。一种表现出这种能力的物种是Elphidium excavtum，这是德国基尔峡湾的常见有孔虫。基尔峡湾（Kiel Fjord）受多条河流喂养，因此形成了盐度剧烈波动的栖息地。在这里，我们测试了食物来源，盐度和光照方式对这种带有kleptoplast的有孔虫的食物摄取（通过¹⁵ N 和¹³ C藻类摄取）的影响。在我们的研究E. excavatum在三个盐度水平（15，20和25）在实验室中培养，并从食物来源的C和N的摄取 杜氏盐藻（绿藻）和Leyanella根结线虫（硅藻）随着时间的推移，测定（后3,5和7  d） 。所述物种是非常良好适应于采样区的当前盐度，因为这两个藻N和C的摄取最高，为20的盐度似乎E. excavatum比具有更高的盐度下应对更好。绿藻D. tertiolecta吸收的C量 显示出盐度的趋向效应，在盐度为20时达到峰值。氮的吸收在盐度为20时也最高，并随时间稳定增加。相反，硅藻吸收了C 盐度最高的沙雷氏菌在15时最高。我们发现绿藻和硅藻对碳和氮的吸收没有总体上的显着差异。此外，将光-暗节奏为16：8  h的食物摄取与连续黑暗进行了比较。黑暗度对藻类碳和氮的吸收有负面影响，并且这种影响随着孵育时间的增加而增加。饥饿的实验表明，食物摄取的刺激后7  d。总而言之，可以得出结论，大肠埃希菌 能很好地将盐度变化降低到较低水平。为了在光状况的变化，我们发现，减光引起摄取C和N的降低 E. excavatum。