Assimilation of upwelled nitrate by small eukaryotes in the Sargasso Sea
Assimilation of upwelled nitrate by small eukaryotes in the Sargasso Sea
复制标题
DOI：
10.1038/ngeo1265
复制
发表时间：
2011-10-01
影响因子：
18.3
通讯作者：
Sigman, Daniel M.
中科院分区：
文献类型：
--
作者：
Fawcett, Sarah E.;Lomas, MichaelW.;Sigman, Daniel M.
浮游植物的生长可能因缺乏生物可利用的氮（例如硝酸盐和铵）而受到限制。在副热带海洋环流中，水柱分层阻碍了硝酸盐向上流入地表水。据推测，这些水域中的浮游植物很大程度上依赖于有机物分解过程中回收的铵和其他形式的氮。在这里，我们利用流式细胞术分离了2008年和2009年夏季从马尾藻海表层水中采集的原核和真核浮游植物，并分析了它们各自的氮同位素比率。我们发现原核生物的 N-15 与 N-14 的比例均较低，即 delta N-15，这与它们对回收氮的依赖一致。相比之下，尺寸小于 30 μm 的小型真核浮游植物的 Delta N-15 更高且变化更大，其平均值与底层亚热带模式水中的硝酸盐相似。对于夏季的马尾藻海，我们估计小型真核生物从上涌的硝酸盐中获取一半以上的氮。此外，我们的数据支持以下观点：下沉物质主要来自真核而非原核浮游植物生物量。
Phytoplankton growth is potentially limited by the scarcity of biologically available forms of nitrogen such as nitrate and ammonium. In the subtropical ocean gyres, water column stratification impedes the upward flux of nitrate to surface waters. Phytoplankton in these waters are assumed to rely largely on ammonium and other forms of nitrogen recycled during the breakdown of organic matter. Here, we use flow cytometry to separate prokaryotic and eukaryotic phytoplankton collected from Sargasso Sea surface waters in the summers of 2008 and 2009, and to analyse their respective nitrogen isotope ratios. We show that prokaryotes have a uniformly low ratio of N-15 to N-14, delta N-15, consistent with their reliance on recycled nitrogen. In contrast, small eukaryotic phytoplankton, less than 30 mu m in size, have a higher and more variable delta N-15, with a mean value similar to that of nitrate in underlying Subtropical Mode Water. For the summertime Sargasso Sea, we estimate that small eukaryotes obtain more than half of their nitrogen from upwelled nitrate. In addition, our data support the view that sinking material derives largely from eukaryotic, not prokaryotic, phytoplankton biomass.