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首页> 外文期刊>Estuarine Coastal and Shelf Science >Effects of mixing-induced irradiance fluctuations on nitrogen uptake in size-fractionated coastal phytoplankton communities
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Effects of mixing-induced irradiance fluctuations on nitrogen uptake in size-fractionated coastal phytoplankton communities

机译：混合诱导的辐照度波动对大小分级的沿海浮游植物群落氮吸收的影响

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In coastal waters subjected to strong tidal forcing, phytoplankton populations are exposed to highly variable light regimes. To grow under such fluctuating light environments, phytoplankton adjust their physiological properties. Here, we investigated nitrogen (N) uptake patterns in the western English Channel to determine whether phytoplankton modify their physiological processes involved in N uptake in response to changing irradiance conditions induced by spring-neap tidal cycles. Nitrate (NO3-) and ammonium (NH4+) uptake kinetics as a function of irradiance (V-N-E curves) were assessed using N-15 tracer techniques on two size fractions (<10 and >10 mu m) of phytoplankton collected at 50% and 1% of surface irradiance during two spring-neap tidal cycles. Overall, the results showed that both small and large phytoplankton, whatever their vertical position in the water column, increased their maximum uptake capacity and their light utilization efficiency for the two N substrates following the decrease in vertical mixing intensity. Moreover, the improvement of irradiance conditions at neap tides was of greater benefit for the larger cells than for the smaller ones and was more favorable for NOT uptake than for NH4+ uptake. These findings show that the light regime fluctuation resulting from the relaxation of tidal mixing during spring-neap tidal cycle leads to profound physiological adjustments of N uptake processes in phytoplanlcton communities. They suggest that the changes in NO3- uptake by large phytoplankton associated with the fortnightly spring-neap tidal cycle can account for most of the deviation in background productivity in the western English Channel which is based on NH4+ and is dominated by small cells. The dynamic light regime inherent to macrotidal coastal ecosystems could therefore determine, to a large extent, the importance of new vs. regenerated production as well as the size structure of the phytoplankton community. (C) 2014 Elsevier Ltd. All rights reserved.
机译：在遭受强潮强迫作用的沿海水域中，浮游植物种群暴露于高度可变的光照下。为了在这种波动的光照环境下生长，浮游植物会调节其生理特性。在这里，我们调查了西部英吉利海峡的氮（N）吸收模式，以确定浮游植物是否响应春季潮汐潮汐周期引起的辐照条件变化来改变其参与N吸收的生理过程。使用N-15示踪技术评估了两个大小比例（<10和> 10μm）浮游植物的硝酸盐（NO3-）和铵（NH4 +）吸收动力学与辐照度的函数关系（VNE曲线），分别以50％和1两个春季小潮周期的表面辐照度的百分比。总体而言，结果表明，无论大小浮游植物，无论其在水柱中的垂直位置如何，随着垂直混合强度的降低，它们对两种氮基质的最大吸收能力和光利用率均得到提高。此外，在潮汐条件下，辐照条件的改善对较大的细胞比对较小的细胞有更大的好处，并且对NO的吸收比对NH4 +的吸收更有利。这些发现表明，春季潮汐潮汐周期中潮汐混合的松弛导致的光态波动导致了浮游植物群落对氮吸收过程的深刻生理调节。他们认为，大型浮游植物对NO 3吸收的变化与每两周的春季-潮汐潮汐周期有关，这可以解释西部英吉利海峡以NH 4+为基础且以小细胞为主的背景生产力的大部分偏差。因此，潮汐沿海生态系统固有的动态光照机制在很大程度上可以决定新生产与再生生产之间的重要性以及浮游植物群落的大小结构。 （C）2014 Elsevier Ltd.保留所有权利。

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