Extensive bloom of a N2-fixing diatom/cyanobacterial association in the tropical Atlantic Ocean
Extensive bloom of a N2-fixing diatom/cyanobacterial association in the tropical Atlantic Ocean
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DOI：
10.3354/meps185273
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发表时间：
1999-01-01
影响因子：
2.5
通讯作者：
Capone, DG
中科院分区：
文献类型：
--
作者：
Carpenter, EJ;Montoya, JP;Capone, DG
1996年秋天，我们在南美洲东北海岸2500公里的巡航路线上遇到了大量的殖民地藻华。每个硅藻细胞都含有异囊、固定n -2的胞内蓝藻内共生菌richhelia。表面黎切菌杂泡（和细丝）密度从开花时的10(6)杂泡1（-1）增加。总丰度从花外的10(6)个m（-2）到花内的10（10）个m（-2）不等。初级生产速率平均为1.2 g C m(-2) d(-1)，高于贫营养开阔海域的典型水平。在开花期间，黎切菌/半穗菌结合对N-2的固定向水柱平均增加了45 mg N m(-2) d（-1）。在开花过程中，NH4+吸收量占总氮吸收量的比重从0增加到42%。richhelia对N-2的固定超过了通过深水NO3扩散产生的“新”N通量的估计，加上蓝藻Trichodesmium对N-2的额外固定，可以在水华期间通过水柱提供约25%的总N需求。水体中悬浮颗粒和浮游动物在N-15中被消耗，反映了N-2固定对浮游N收支的主要贡献。正如卫星图像所显示的那样，水华在空间上很广泛，据计算，它对光区的贡献约为0.5 Tg N。这种水华可能代表了一种重要的、以前未被认识到的新氮来源，以支持营养贫乏的热带水域的初级生产。此外，这表明异囊蓝藻也可以在海洋水柱环境中对N做出定量的重要贡献。
We encountered an extensive bloom of the colonial diatom Hemiaulus hauckii along a 2500 km cruise track off the NE coast of South America in autumn 1996. Each diatom cell contained the heterocystous, N-2-fixing cyanobacterial endosymbiont Richelia intracellularis. Surface Richelia heterocyst (and filament) densities increased from 10(6) heterocyst l(-1) in the bloom. Total abundance ranged from 10(6) heterocyst m(-2) outside the bloom to over 10(10) heterocyst m(-2) within the bloom. Rates of primary production averaged 1.2 g C m(-2) d(-1), higher than typical for oligotrophic open ocean waters. N-2 fixation during the bloom by the Richelia/Hemiaulus association added an average of 45 mg N m(-2) d(-1) to the water column. The relative importance of NH4+ uptake over the course of the bloom increased from 0 to 42% of total N uptake by the Hemiaulus/Richelia association. N-2 fixation by Richelia exceeded estimates of 'new' N flux via NO3 diffusion from deep water and, together with additional N-2 fixation by the cyanobacterium Trichodesmium, could supply about 25% of the total N demand through the water column during the bloom. Suspended particles and zooplankton collected within the bloom were depleted in N-15, reflecting the dominant contribution of N-2 fixation to the planktonic N budget. The bloom was spatially extensive, as revealed by satellite imagery, and is calculated to have contributed about 0.5 Tg N to the euphotic zone. Such blooms may represent an important and previously unrecognized source of new N to support primary production in nutrient-poor tropical waters. Furthermore, this bloom demonstrates that heterocystous cyanobacteria can also make quantitatively important contributions of N in oceanic water column environments.