Controls on iron availability to marine phytoplankton

二氧化碳（CO2）等人为温室气体的排放正在导致气候变化、全球变暖和海洋酸化。被称为浮游植物的微小植物生活在海洋表层，吸收了全球50%的二氧化碳，并提供了50%用于初级生产的新氮。除了光和主要营养物质外，浮游植物的生长还受到金属铁（Fe）供应的强烈影响，因为金属是光合作用和固氮所必需的，但在开阔的海洋中非常稀缺。铁是如此重要，以至于在缺铁地区播种铁被认为是一种通过提高浮游植物对大气二氧化碳的生物吸收来控制气候变化的可行方法。为了了解铁是如何控制大气二氧化碳水平和海洋生产力的，重要的是首先要尝试了解对海洋浮游植物可利用金属的控制。普遍的观点是，金属的生物利用度取决于其在环境散装水中的化学形态（即金属形态）；然而，我们最近的研究数据与长期存在的范式不一致。在拟议的项目中，我将通过使用新颖的纳米技术和跨学科方法，通过研究直接围绕浮游植物细胞的微米尺度空间的藻圈中的铁形态来挑战这种长期存在的范式。浮游植物直接从藻圈中吸收包括铁在内的营养物质，而不是直接从大量海水中吸收，然而在这个微尺度空间中铁的形态以前没有研究过。对藻圈铁形态认识的缺乏可能导致对当前和未来海洋铁有效性的严重低估或高估，并导致对海洋生态系统如何响应气候变化的错误预测。该跨学科项目将为研究浮游植物获取铁元素的基本过程提供新的视角，并有助于提高政府间气候变化专门委员会等国际机构评估行星系统对气候变化敏感性的能力和准确性。

Anthropogenic greenhouse gas emissions such as carbon dioxide (CO2) are causing climate change, global warming, and ocean acidification. Microscopic plants called phytoplankton, living in the surface oceans, sequester 50% of global CO2 and supply >50% of new nitrogen used for primary production. Other than light and major nutrients, phytoplankton growth is strongly influenced by availability of the metal iron (Fe), because the metal is essential for photosynthesis and nitrogen fixation, but is very scarce in the open ocean. Iron is so important that seeding the metal into Fe-poor areas has been proposed as a viable method for controlling climate change by enhancing bio-uptake of atmospheric CO2 by phytoplankton. In order to understand how Fe controls atmospheric CO2 levels and oceanic productivity, it is important to first attempt to understand the controls on availability of the metal to marine phytoplankton. The prevailing view is that metal bioavailability depends upon its chemical forms (i.e., metal speciation) in ambient bulk waters; however, data from our recent studies are inconsistent with the long-standing paradigm. In the proposed project, I will challenge this long-standing paradigm by studying the Fe speciation in the phycosphere, a micrometer scale space which directly surrounds a phytoplankton cell, through the use of novel nano-technologies and inter-disciplinary approaches. Phytoplankton directly take up nutrients including Fe from the phycosphere, rather than directly from bulk seawater, however the Fe speciation in this micro-scale space has not previously been studied. The lack of knowledge on phycosphere Fe speciation would potentially result in serious under or overestimation of oceanic Fe availability in current and future oceans, and lead to erroneous prediction of how ocean ecosystem responds to Climate Change. The interdisciplinary project will provide a new view on the fundamental processes in Fe acquisition by phytoplankton, and it will certainly help improve the capability and accuracy of international agencies such as the Intergovernmental Panel on Climate Change to assess the sensitivity of planetary system to Climate Change.