Effects of Ocean Acidification on Nutrient Availability and Requirements in Phytoplankton

大气中二氧化碳的持续积累对海洋最确定的影响是二氧化碳浓度的增加，溶解的二氧化碳活度([CO2])，以及表层水域pH的下降。这种“酸化”可能会影响浮游植物营养物质的可获得性以及生物体的生理学。因此，从生物学的角度来看，二氧化碳增加带来的海洋化学变化将与物理变化相互作用，这些变化有望改变营养物质对表层的输入。对初级生产力和向深海输出有机物的净影响代表了对大气CO2增加的潜在反馈。在这个项目中，普林斯顿大学的研究人员将量化表层海水中[CO2]持续增加和pH下降对海洋浮游植物宏观和微观营养物质的需求和有效性的影响，以及由此导致的生物生长和元素组成的变化。根据我们对浮游植物生理学的了解和一些初步数据，[二氧化碳]的增加可能会提高生物利用铁和氮的效率，铁和氮是海洋中两种主要的限制营养物质。PH的降低可能会改变必需痕量金属的有效性，特别是铁，因为它们在介质中的化学形态发生变化，并通过降低胞外酶的活性从有机来源吸收大量营养物质。为了揭示海洋酸化对浮游植物的复杂影响，他们最初将基于三个不同的假设进行三个方面的研究：1)酸化降低浮游植物细胞对铁的吸收速率，同时提高其铁的利用效率(前者是因为低pH值，后者是因为高[CO2])；2)酸化提高了N限制性浮游植物的C/N比，增加了N的利用效率和富C化合物的储存；3)酸化降低了浮游植物利用有机磷的能力，这是因为碱性磷酸酶的比活性和酶合成所需的锌有效性降低。工作计划包括相辅相成的实验室和现场实验，以检验各种假说并阐明潜在的生化机制，以便可以推断结果。进一步的工作将取决于初步结果。更广泛的影响：该项目涉及一个社会非常关注的问题，因此，预计研究结果将引起广泛的兴趣。除了通常的研究和教育活动自然包含在这类项目之外，一个具体目标是在科学界内外更广泛地加强科学理解和教育。通过多种合作，该项目将在对二氧化碳和海洋浮游植物相互作用的不同方面感兴趣的不同社区之间架起桥梁--从建模人员和海洋海洋学家到藻类生理学家和生物化学家。这一项目的主题还应对旨在改善理科学校教师教育的外联活动有效，并为他们提供提高其教学效果的材料。一个实习项目将为新泽西州社区大学的学生提供实践研究经验。

The most certain effect on the ocean of the ongoing build up of atmospheric CO2 is an increase in the CO2 concentration, dissolved CO2 activity ([CO2]), and a decrease in the pH of surface waters. This "acidification" will likely affect the availability of nutrients to phytoplankton as well as the physiology of the organisms. Thus, from a biological point of view, the chemical changes in ocean chemistry brought about by the CO2 increase will interact with the physical changes, which are expected to modify the input of nutrients to the surface. The net effect on primary production and the export of organic matter to the deep represents a potential feedback to the increase in atmospheric CO2.In this project, researchers at Princeton University will quantify the effects of the ongoing increase in [CO2] and the decrease in pH in surface seawater on the requirements and availability of macro- and micro-nutrients in marine phytoplankton, and the resulting changes in the growth and elemental composition of the organisms. Based on what we know of the physiology of phytoplankton and some preliminary data, an increase in [CO2] likely to increase the efficiency with which the organisms utilize Fe and N, two of the principal limiting nutrients in the ocean. A decrease in pH is likely to change the availability of essential trace metals, particularly Fe, by changing their chemical speciation in the medium, and the uptake of macro-nutrients from organic sources by decreasing the activity of extracellular enzymes.To unravel the complex effects of ocean acidification on phytoplankton they will pursue initially three avenues of research based on three distinct hypotheses: 1) acidification lowers the rate of Fe uptake by phytoplankton cells and simultaneously increases their Fe use efficiency (the former because of low pH, the latter because of high [CO2]); 2) acidification increases the C:N ratio of N-limited phytoplankton because of an increase in N use efficiency and the storage of C-rich compounds; and 3) acidification decreases the ability of phytoplankton to use organic sources of P because of a decrease in the specific activity of alkaline phosphatase and in Zn availability for synthesis of the enzyme. The plan of work consists of mutually reinforcing laboratory and field experiments to test the various hypotheses and to elucidate the underlying biochemical mechanism so that the results can be extrapolated. Further work will depend on initial results. Broader Impacts: This project addresses an issue of great concern to society and the results of the research are thus expected to generate wide interest. Beyond the usual research and educational activities that are naturally embedded in such a project, a specific goal is to enhance scientific understanding and education more broadly within and outside the scientific community. Through multiple collaborations, this project will serve to bridge different communities interested in diverse aspects of the interactions between CO2 and marine phytoplankton-- from modelers and seagoing oceanographers to algal physiologists and biochemists. The topic of this project should also be effective for outreach activities designed to improve the education of science school teachers and provide them with material to enhance the effectiveness of their teaching. An internship program will provide hands-on research experience to students from community colleges in New Jersey.