Max-Planck-Institute for Ornithology, Schlossallee 2, D-78315 Radolfzell, Germany.
Rapid Commun Mass Spectrom. 2011 Jul 30;25(14):2089-94. doi: 10.1002/rcm.5094.
Macrophytes are at the base of many lake food webs providing essential food resources for animals at higher trophic level, such as invertebrates, fish and waterbirds. However, data regarding the spatiotemporal variation in isotopic composition of macrophytes are generally missing. We measured the carbon and nitrogen stable isotope ratios of Charophytes at Lake Constance, where they constitute a major food source for waterbirds. Our data reveal seasonal and site-specific differences as well as depth-specific variations in isotopic carbon values within the littoral zone. Charophytes were enriched in (13)C at sites of higher productivity: the δ(13)C values were high in summer, at shallow and at relatively nutrient-rich sites, and comparatively low in winter, and in deeper and nutrient-poorer sites. In contrast, no temporal or spatial trend was found to explain the variability in the isotopic nitrogen values. These results imply that the seasonal timing of food intake (relative to turnover rates of consumers tissue) and the potential depth of foraging need to be taken into account when calculating the relative contribution of energy sources to diets of consumers such as waterbirds.
大型藻类处于许多湖泊食物网的底部，为处于较高营养级的动物（如无脊椎动物、鱼类和水鸟）提供重要的食物资源。然而，关于大型藻类稳定同位素组成的时空变化的数据通常是缺失的。我们测量了康斯坦茨湖的轮藻的碳和氮稳定同位素比值，轮藻是水鸟的主要食物来源。我们的数据显示，在湖岸带存在季节性和特定地点的差异以及在特定深度的碳同位素值的变化。在生产力较高的地点，轮藻的（13）C 富集度更高：（13）C 值在夏季较高，在浅水区和相对富营养的地点较高，在冬季和较深且营养较差的地点较低。相比之下，没有发现时间或空间趋势可以解释氮同位素值的可变性。这些结果表明，在计算水鸟等消费者的食物源对能量的相对贡献时，需要考虑食物摄入的季节性时间（相对于消费者组织的周转率）和潜在的觅食深度。
