Ocean Acidification: Effect on the Availability of Divalent Trace Metals to Phytoplankton

人为CO2溶解到表层海水中所引起的海水化学变化将影响浮游植物的生长，从而影响海洋食物网的功能。二氧化碳增加引起的酸化（pH值降低）的一个影响是必需微量金属的化学形态和生物利用度的变化。最近对天然海水样品的研究显示了一个意想不到的结果：锌（Zn）的生物利用度在低pH下降低，锌是一种在浮游植物中起关键酶促作用的金属。锌和其他必需金属一样，在海水表面与有机络合剂结合。酸化预计会降低锌络合的程度，从而增加其对浮游植物的可利用性。这种锌生物利用度的增加确实是在酸化的实验室介质中看到的，其中锌与已知的络合剂结合。在这个项目中，普林斯顿大学的一个研究小组将测试自然海水酸化样品中锌生物利用度的矛盾下降是否可以解释为锌从弱和生物可利用的有机络合物向强不可用络合物的转变。这种“双配体机制”的原理证明已在实验室系统中获得，原则上可推广到其他生物有用的微量金属，如锰、钴、镍、铜和镉。实验将包括以不同ph值的天然表面海水样品进行平行的化学和生物学实验：(i)电化学测量弱配体和强配体对Zn和Cd的络合作用，以及（ii）模拟浮游植物物种和自然种群对Zn和Cd的吸收实验。更广泛的影响：该项目直接关系到社会高度关注的一个问题，并将进一步加深我们对全球海洋酸化可能产生的生态影响的理解，这是大气中二氧化碳持续增加的不可避免的后果。它还将增强我们对控制海洋浮游植物必需微量金属生物可利用性的过程的理解。因此，预计研究结果将引起广泛的兴趣，其中一些可能会发表在传播广泛和影响很大的期刊上。它们还将被纳入首席研究员在本科和研究生阶段教授的两门课程，以及在当地一所小学的“科学日”活动中。

The ongoing changes in seawater chemistry caused by the dissolution of anthropogenic CO2 into surface seawater will affect the growth of phytoplankton and, hence, the functioning of marine food webs. One effect of the acidification (lowering of pH) caused by the increasing CO2 is a change in the chemical speciation and bioavailability of essential trace metals. Recent work with natural seawater samples has shown an unexpected result: a decrease at low pH in the bioavailability of zinc (Zn), a metal that plays key enzymatic roles in phytoplankton. Zinc, like other essential metals, is known to be bound to organic complexing agents in surface seawater. Acidification is expected to decrease the extent of Zn complexation and thus augment its availability to phytoplankton. Such increase in Zn biovailability is indeed seen upon acidification of laboratory media in which Zn is bound to a known complexing agent.In this project, a research team at Princeton University will test whether the paradoxical decrease in Zn biovailabilty seen in acidified samples of natural seawater is explained by a shift of Zn from weak and bioavailable organic complexes to strong unavailable complexes. Proof of principle for such a "two-ligand mechanism" has been obtained in laboratory systems and is generalizable in principle to other bio-useful trace metals such as manganese, cobalt, nickel copper and cadmium. The experiments will involve parallel chemical and biological experiments with natural surface seawater samples at different pHs: (i) electrochemical measurements of Zn and Cd complexation by weak and strong ligands, and ( ii) Zn and Cd uptake experiments with model phytoplankton species and natural populations. Broader impacts: This project is directly relevant to an issue of great concern to society and will further our understanding of the possible ecological effects of global ocean acidification, an ineluctable consequence of the ongoing increase in atmospheric CO2. It will also augment our understanding of the processes that control the bioavailability of essential trace metals to marine phytoplankton. The results of the research are thus expected to generate wide interest and some will likely be published in journals with broad dissemination and high impact. They will be also incorporated into two of the courses taught by the Principal Investigator at the undergraduate and graduate levels and in a "Science day" event at a local elementary school.