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The influence of iron and siderophores on eukaryotic phytoplankton growth rates and community composition in the Ross Sea

机译：铁和铁载体对罗斯海真核浮游植物生长速率和群落组成的影响

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Shipboard manipulation experiments were conducted during the 2011 austral summer to assess the responses of eukaryote phytoplankton assemblages in the Ross Sea to ferric chloride, Fe-siderophore complexes, and apo-siderophore addition. An emphasis was placed on the model catecholate siderophore enterobactin, including limited experiments to test hypothesized interactions between Cu availability and the capacity to access Fe from Fe-enterobactin. Stations included those on Pennell Bank, along the western flank of Pennell Bank and at the shelf break. Growth rate estimates based on chlorophyll a (chl a) accumulation and nitrate drawdown under constant illumination, as well as silicate:nitrate (Si:N) drawdown and variable fluorescence (Fv/Fm), were used to evaluate bulk phytoplankton responses to Fe and siderophores. Responses to ferric chloride, copper and Fe-enterobactin plus Cu manipulations revealed widespread Fe limitation but no evidence of Cu limitation of enterobactin availability. These results were consistent with ambient surface water dissolved Fe concentrations ranging from 110 to 320 pM, known to limit Southern Ocean diatoms, and with dissolved Cu profiles showing non-limiting surface water concentrations of similar to 1.8 nM. Fe-enterobactin additions (2 nM) stimulated growth of Ross Sea populations to the same extent as ferric chloride based on either chl a accumulation or nitrate drawdown, except on Pennell Bank (station 7) where the chl a-based growth rate was slightly lower. All Fe-enterobactin treatments resulted in decreases in Si:N drawdown and increases in Fv/Fm by the end of the incubation. Given the general availability of Fe-enterobactin among these treatments, we hypothesized that apo-enterobactin might be an effective shuttle from less available reservoirs of Fe, and therefore increase Fe availability. Apo-enterobactin led to a modest improvement in nitrate-based growth at one station. We amplified the V7-V9 hypervariable region of 18S ribosomal DNA with high phylogenetic resolution to investigate whether the source of Fe elicited a shift in community composition, which would suggest clade-specific capacities to access siderophore bound Fe. Despite differences in community structure at Pennell Bank (dominated by Chaetoceros clades) and other locations (dominated by Pseudonitzschia), there was no evidence for changes in community composition during incubations in response to ferric chloride or enterobactin treatments. Preliminary results from one incubation suggest that Fe limitation was relieved with Fe added as any one of four model siderophores (enterobactin, ferrichrome, ferrioxamine, and pyoverdin) of differing Coordination, stability and dissociation rates, suggesting that extant species may be able to utilize Fe, either directly or indirectly, from a variety of strong ligands on these time scales. (C) 2014 Elsevier B.V. All rights reserved.
机译：在2011年南方夏季进行了舰上操纵实验，以评估罗斯海中的真核生物浮游生物组合对氯化铁，铁-铁载体和脱辅铁-铁载体的响应。重点放在了儿茶酚型铁载体肠球菌素模型上，包括有限的实验来检验假设的铜可用性与从铁肠杆菌素获得铁的能力之间的相互作用。站点包括Pennell Bank上，Pennell Bank西侧和货架处的站点。基于叶绿素a（chla）积累和硝酸盐在恒定光照下的沉降以及硅酸盐：硝酸盐（Si：N）的沉降和可变荧光（Fv / Fm）的生长速率估算，用于评估浮游植物对Fe和Fe的响应。铁载体。对氯化铁，铜和铁-肠杆菌素加铜操作的反应显示出广泛的铁限制，但没有证据表明肠杆菌素可利用性有铜限制。这些结果与周围地表水中溶解的铁浓度范围在110至320 pM之间（已知限制南大洋硅藻）以及溶解的铜剖面显示出非限制性地表水浓度接近1.8 nM一致。添加铁-肠杆菌素（2 nM）刺激了罗斯海种群的增长，其增长速度与基于氯化物累积或硝酸盐沉降的氯化铁相同，但佩纳尔河岸（7号站）的生长速率略低。在培养结束时，所有铁肠杆菌素处理均导致Si：N下降量减少，Fv / Fm增加。鉴于这些治疗方法中铁-肠杆菌素的普遍可用性，我们假设脱辅基-肠杆菌素可能是来自较少可用铁储库的有效穿梭，因此增加了铁的利用率。载脂蛋白-肠杆菌肽在一个站位导致基于硝酸盐的生长适度改善。我们以高系统发育分辨率扩增了18S核糖体DNA的V7-V9高变区，以研究Fe的来源是否引起了群落组成的转变，这暗示了进化枝特定的能力来访问铁载体结合的Fe。尽管Pennell Bank（以Chaetoceros进化枝为主）和其他地区（以Pseudonitzschia为主）的群落结构存在差异，但没有证据表明在孵化过程中响应氯化铁或肠抑菌素治疗的群落组成发生变化。一次孵化的初步结果表明，添加铁可以缓解铁的局限性，因为四种配位，稳定性和解离速率不同的模型铁载体（肠杆菌素，铁铬铁，铁氧胺和pyoverdin）中的任何一种，都表明现有物种可能能够利用铁在这些时间尺度上直接或间接地来自各种强配体。 （C）2014 Elsevier B.V.保留所有权利。

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