High rates of ammonium recycling drive phytoplankton productivity in the offshore Mississippi River plume
High rates of ammonium recycling drive phytoplankton productivity in the offshore Mississippi River plume
复制标题
高铵回收率提高了密西西比河近海羽流中浮游植物的生产力
DOI：
10.3354/ame035175
复制
发表时间：
2004
影响因子：
1.4
通讯作者：
M. Gray
中科院分区：
文献类型：
--
作者：
B. Wawrik;J. Paul;D. Bronk;David E. John;M. Gray
作为密西西比河近海羽流碳固定调节综合研究的一部分，我们测量了沿着密西西比河三角洲羽流轴从近海到近岸的地表羽流水中 15 N 标记的铵和硝酸盐的吸收率。羽流中硝酸盐的浓度范围为 0.19 至 2.5 µM，浓度最高的主要是在岸边站，而铵的浓度范围为 0.17 至 0.44 µM，空间变异性很小。铵吸收率范围为 16.5 至 260 nM h -1 ，并显示出从近海到密西西比三角洲值增加的强烈趋势。相反，硝酸盐吸收率范围为 3.2 至 25 nM h -1 。在低铵浓度和高硝酸盐存在的情况下，高铵吸收率是通过提高铵再生率而实现的，该再生率超过羽流中铵吸收率的1.7至5.7倍。羽流表现出相对较低的 f 比，并且通过流式细胞术测定还含有升高水平的聚球藻和高水平的 IA（α-蓝细菌）rbcL 转录物。这些数据表明，在密西西比河近海羽流中观察到的碳固定的主要部分代表了高铵再生率支持的循环生产。
As part of an integrated study of the regulation of carbon fixation in the offshore Mississippi River plume, we measured the rates of 15 N-labeled ammonium and nitrate uptake in the surface plume waters from offshore to nearshore along the plume axis towards the Mississippi Delta. Concentrations of nitrate in the plume ranged from 0.19 to 2.5 µM with the highest concentrations primarily in the shoreward stations, while ammonium ranged from 0.17 to 0.44 µM, showing little spatial variability. Rates of ammonium uptake ranged from 16.5 to 260 nM h -1 , and showed a strong trend of increasing values from offshore towards the Mississippi Delta. In contrast, nitrate uptake rates ranged from 3.2 to 25 nM h -1 . The high rates of ammonium uptake in the presence of low ammo- nium concentrations and elevated nitrate was made possible by elevated rates of ammonium re- generation that exceeded ammonium uptake by 1.7 to 5.7-fold in the plume. The plume exhibited relatively low f-ratios and also contained elevated levels of Synechococcus as determined by flow cytometry and high levels of form IA (α -cyanobacterial) rbcL transcripts. These data suggest that a major portion of the carbon fixation observed in the offshore Mississippi River plume represents recycled production supported by high rates of ammonium regeneration.