Differential Responses of Eukaryotic Phytoplankton to Nitrogenous Nutrients in the North Pacific Subtropical Gyre
Differential Responses of Eukaryotic Phytoplankton to Nitrogenous Nutrients in the North Pacific Subtropical Gyre
复制标题
DOI：
10.3389/fmars.2018.00092
复制
发表时间：
2018-03
影响因子：
3.7
通讯作者：
Y. Rii;R. Bidigare;M. Church
中科院分区：
文献类型：
--
作者：
Y. Rii;R. Bidigare;M. Church
固定无机氮(N)在亚热带大洋环流光照较好的区域持续缺乏，其供应在控制浮游植物生产力方面起着重要作用。在北太平洋亚热带环流(NPSG)进行的一系列实验中，我们研究了硝酸盐(NO3-)、氨(NH4+)或尿素与磷酸盐和硅酸一起添加时，初级生产力和真核浮游植物群落结构的变化。总体而言，我们观察到在氮素添加后，14C初级生产力(~2-到27倍)和叶绿素a浓度(~2-到7倍)都有很大的提高。大部分生理反应是由于较大的浮游植物(>；3微米)，其对初级生产力的贡献增加了~2倍，而微藻浮游植物(0.2-3微米)的贡献下降了类似的比例。在春季、夏季和冬季进行的五个实验表明，浮游植物群落结构对氮素供应的响应明显依赖于季节。在夏季，光合色素分析和18S rDNA高通量测序都证明，施氮后羽状硅藻数量显著增加。例如，在添加N底物后，岩藻黄质(一种硅藻色素生物标志物)的浓度增加了23到49倍，属于假硝化细菌的rRNA基因的相对丰度从微不足道的(约0.3%)增加到3微米浮游植物组合的30%-60%。然而，与夏季观察到的硅藻驱动的反应不同，春季和冬季进行的实验表明，19‘-丁酰氧岩藻黄质(一种中上层植物色素生物标记物)的浓度大幅增加，以及聚集在Pelagomonas之间的rRNA基因的相对丰度增加。总体而言，我们的研究结果显示，在一年中不同时间进行的实验中，主要类群的反应存在差异，并伴随着对浮游植物多样性模式的影响。此外，在叶绿素a、14C初级生产和真核浮游植物群落组成方面的总体响应似乎在很大程度上与添加的N底物的类型无关。我们的结果突出了氮有效性在塑造贫营养NPSG表层水域真核浮游植物多样性中的作用的季节尺度差异。
Fixed inorganic nitrogen (N) is persistently scarce in the well-lit regions of the subtropical ocean gyres and its supply plays an important role in controlling phytoplankton productivity. In a series of experiments conducted in the North Pacific Subtropical Gyre (NPSG), we examined changes in primary productivity and eukaryotic phytoplankton community structure in response to additions of nitrate (NO3-), ammonium (NH4+), or urea in conjunction with phosphate and silicic acid. Overall, we observed large increases in rates of 14C-primary productivity (~2- to 27-fold) and concentrations of chlorophyll a (~2- to 7-fold) following N addition. Much of the physiological response was due to larger (>3 µm) phytoplankton, whose contributions to primary productivity increased ~2-fold while picophytoplankton (0.2-3 µm) contributions decreased by a similar proportion. Five experiments, conducted in the spring, summer and winter, revealed apparent seasonally-dependent responses in phytoplankton community structure to N availability. During the summer, pennate diatoms increased significantly following N addition as evidenced by both photosynthetic pigment analyses and high-throughput sequencing of 18S rDNA. For example, following the addition of N substrates, concentrations of fucoxanthin (a diatom pigment biomarker) increased between 23- and 49-fold, and relative abundances of rRNA genes belonging to Pseudo-nitzschia increased from negligible (~0.3%) to 30-60% of the >3 µm phytoplankton assemblage. However, unlike the diatom-driven responses observed in the summer, experiments conducted in the spring and winter demonstrated large increases in concentrations of 19’-butanoyloxyfucoxanthin (a pelagophyte pigment biomarker) together with increases in the relative abundance of rRNA genes clustering among Pelagomonas. Overall, our findings revealed differences in the responses of major taxa during experiments conducted in different times of the year, with concomitant impacts on patterns of phytoplankton diversity. In addition, the overall responses in chlorophyll a, 14C-primary production, and eukaryotic phytoplankton community composition appeared largely independent of the type of N substrate added. Our results highlight seasonal-scale differences on the role of N availability in shaping eukaryotic phytoplankton diversity in the surface waters of the oligotrophic NPSG.