Abstract. 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 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, 25 PSU) and uptake of C and N (food source: Dunaliella tertiolecta) were measured over time (after 3, 5, 7 days). The species was very well adapted to the current salinity of the sampling region, as both, algal N and C uptake was highest at 20 PSU. 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 marginal significant effect of salinity, peaking at 20 PSU. Nitrogen uptake was also highest at 20 PSU and steadily increased with time. In contrast, C uptake from the diatom L. arenaria was highest at 15 PSU and decreased at higher salinities. We found no overall significant differences in C and N uptake from green algae versus 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 days. 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，光照和食物来源对带有鳞状动植物的有孔虫中碳和氮吸收的影响

摘要。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。基尔峡湾由多条河流喂养，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在实验室中以三种盐度（15、20、25 PSU）进行培养，并随时间（3、5、7天后）测量了C和N（食物来源：杜氏盐藻）的吸收。该物种非常适合采样区域的当前盐度，因为藻类N和C的吸收均在20 PSU时最高。盐度低的盐似乎比盐度高的盐更好。从绿藻D. tertiolecta吸收的C量显示出盐度的边际显着影响，在20 PSU达到峰值。氮的吸收量也最高，为20 PSU，并且随时间稳定增长。相反，硅藻L. arenaria吸收了C在15 PSU时最高，在较高盐度时下降。我们发现绿藻和硅藻的C和N吸收量没有总体显着差异。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。饥饿的实验显示7天后刺激食物摄取。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。