Can acidic polysaccharides exuded by diatoms function as iron ligands, increasing the iron availability for diatoms?

硅藻分泌的酸性多糖能否充当铁配体，增加硅藻对铁的利用率？

• 批准号: 5415949
• 负责人: Professorin Dr. Uta Desy Elisabeth Passow
• 金额: --
• 依托单位: Memorial University of Newfoundland
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2003
• 资助国家: 德国
• 起止时间: 2002-12-31 至 2007-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/5415949?language=en
• 关键词: acidic; polysaccharides; exuded; diatoms; function

Of all trace elements, iron has the most profound impact on the biological pump. In many areas of the ocean (HNLC-areas) primary productivity can be limited by iron. In oxygenated waters the dominant redox state for iron is the poorly soluble Fe(III). Organic complexation of Fe(III) by natural ligands increases the overall solubility for iron. The majority of these ligands are not well characterized and their origin and production remain elusive. Diatoms exude acidic polysaccharides abundantly and these acidic polysaccharides, both in their colloidal and paricultate (called TEP) form, may represent an important fraction of the uncharacterized Fe-ligands in the ocean. We propose to investigate the following 4 hypotheses experimentally and in the field: 1. Biologically significant amounts of iron bind to acidic polysaccharides. 2. Diatoms exude acidic polysaccharides in response to iron limitation. The release of these substances is ongoing but may be enhanced by iron limitation (senescence) or by the sudden input of iron relieving cells of iron limitation (leaky cells). 3. The carbohydrate production of diatoms underlies a diel cycle, which influences iron speciation. 4. Iron bound to acidic polysaccharides profits diatoms, either because this iron is directly bioavailable for diatoms, or because binding of iron to these substances, prevents it from precipitation, keeping it in the surface layer, where it is released slowly in a bioavailable form (e.g. after photo-reduction). Understanding the cycling of iron in the ocean is a prerequisite for assessing the long-term effects of iron fertilization for the ocean and for the atmospheric CO2 concentration.

在所有的微量元素中，铁对生物泵的影响最深刻。在海洋的许多区域(HNLC区域)，初级生产力可能会受到铁的限制。在含氧水中，铁的主要氧化还原状态是难溶的Fe(III)。天然配体与Fe(III)的有机络合增加了铁的总溶解度。这些配体中的大多数都没有得到很好的表征，它们的来源和生产仍然难以捉摸。硅藻大量分泌酸性多糖，这些酸性多糖以胶体和细小颗粒(称为TEP)的形式存在，可能是海洋中未表征的铁配体的重要组成部分。我们建议在实验和野外研究以下4个假说：1.生物上有意义的铁与酸性多糖结合。2.硅藻分泌酸性多糖响应铁的限制。这些物质的释放是持续的，但可以通过铁限制(衰老)或通过突然注入铁来解除铁限制的细胞(漏铁细胞)而增强。3.硅藻碳水化合物的产生是一个双循环的基础，它影响铁的形态。4.与酸性多糖结合的铁有利于硅藻，要么是因为这种铁对硅藻是直接生物可利用的，要么是因为铁与这些物质的结合阻止了它的沉淀，使其保持在表层，在那里以生物可利用的形式缓慢释放(例如，在光还原之后)。了解海洋中铁的循环是评估铁肥对海洋和大气二氧化碳浓度的长期影响的先决条件。