Partitioning of C, N and P between particulate and dissolved phases during growth of phytoplankton at different pH.

海洋浮游植物在碳（C）、氮（N）和磷（P）等重要生物元素在大气、海洋和海洋沉积物之间的循环中起着核心作用。在短时间内（数周），浮游植物可以增殖，形成大量的新细胞，这些细胞有助于海洋表面的颗粒有机物（POM）。在此过程中，它们从海水中吸收营养物质（N和P）和二氧化碳（CO2）。这些二氧化碳被大气中溶解在海洋表面的二氧化碳所取代，恢复了长期的海洋-大气平衡。在水华期间，一些细胞被食草动物消耗，支持海洋食物网，而其他细胞则死亡或粘在一起并下沉。到达海洋沉积物的物质有助于“生物碳泵”，它能够在地质时间尺度上掩埋大气中的二氧化碳和其他营养物质。然而，这些并不是同化营养物的唯一命运。在浮游植物生长期间，有机分子从细胞释放到周围的海水中。这些有机物（溶解有机物/ DOM）被细菌降解，再生营养物质并将二氧化碳和其他气候活性（或温室）气体释放到大气中。因此，被同化的营养物质的命运，无论是POM或DOM，对海洋食物网的生产力，对可能从大气中去除的CO2和从海洋表面释放到大气中的温室气体具有重要的影响。在水华期间，POM和DOM之间的浮游植物的营养盐的分配变化很大，虽然我们对这个过程的定量了解是有限的。事实上，没有可靠的定量数据来描述这种与浮游植物细胞健康有关的分区。没有这些数据，我们就无法开发和完善数学模型，使我们能够调查海洋生态系统和全球气候变化的影响。这个项目将解决我们认识上的这一重要不足。在浮游植物大量繁殖期间，伴随营养物质消耗的一个重要因素是海水pH值从8.2增加到8.5以上。最终浮游植物停止运作，如果pH值超过他们的容忍度，与物种演替的影响，在水华繁殖。这一点在模型中通常被忽略。我们没有定量或严格的数据来描述营养限制和pH值升高的组合，这可能会影响驯化过程中的营养分配，从而影响水华的生产力和生物地球化学影响。该项目将专门研究pH值变化对海洋浮游植物生长动态的影响。与水华期间海水pH值升高的时期相反，有证据表明，随着人类活动产生的人为CO2溶解在海洋表层，未来几十年海洋将酸化（pH值福尔斯）。对浮游植物的生长、营养分配以及它们适应相对酸性环境的能力的影响是完全未知的。对海洋环境及其提供的服务的影响值得紧急调查。该项目由斯旺西大学和普利茅斯海洋实验室联合进行，将看到代表性浮游植物的培养物受到代表当今和未来（酸化海洋）情况的不同条件（营养物质可用性，pH值）的影响。描述生物体生长和活动变化的数据将支持数学模型的构建和测试。研究结果将被纳入生态系统模型，将研究海洋生产力和海洋地球化学的影响，改进描述的植物生长活性，和海洋酸化的英国陆架海。

Marine phytoplankton play a central role in the cycling of biologically important elements, such as carbon (C), nitrogen (N) and phosphorous (P) between the atmosphere, ocean and marine sediments. Over short periods (weeks) phytoplankton can proliferate, forming vast blooms of new cells that contribute to the Particulate Organic Matter (POM) in the surface ocean. In so doing, they take up nutrients (N and P) and carbon dioxide (CO2) from seawater. This CO2 is replaced by atmospheric CO2 that dissolves in the surface ocean and restores the long-term ocean-atmosphere balance. During a bloom, some cells are consumed by grazers, supporting marine food webs, while others die or stick together and sink. Material reaching the marine sediment contributes to the 'biological carbon pump' which is capable of burying atmospheric CO2 and other nutrients over geological time scales. However, these are not the only fates for assimilated nutrients. During the growth of phytoplankton, organic molecules are released from the cells to the surrounding seawater. These organics (dissolved organic matter / DOM) are used by bacteria which degrade them, regenerating nutrients and releasing CO2 and other climatically active (or greenhouse) gases to the atmosphere. Consequently, the fate of assimilated nutrients, as either POM or DOM, has important implications for the productivity of marine food webs, for CO2 that may be removed from the atmosphere and for the release of greenhouse gases to the atmosphere from the surface ocean. During blooms, the partitioning of nutrients by phytoplankton between POM and DOM changes substantially although our quantitative understanding of this process is limited. In fact, there are no robust, quantitative data available that describe this partitioning in relation to the health of the phytoplankton cells. Without these data we are unable to develop and refine mathematical models that allow us to investigate the implications for marine ecosystems and for global climate change. This project will address this important shortfall in our understanding. An important factor accompanying the consumption of nutrients during phytoplankton blooms is the increase in seawater pH, from 8.2 to greater than 8.5. Ultimately phytoplankton cease to function if the pH exceeds their tolerance, with implications for species succession during bloom propagation. This aspect is usually ignored in models. We have no quantitative or rigorous data available which describes the combination of nutrient limitation and elevated pH, which is likely to effect nutrient partitioning during the acclimation process, and hence the productivity and biogeochemical impact of the bloom. This project will specifically address the impact of changes in pH upon the growth dynamics of marine phytoplankton. In contrast to periods of elevated seawater pH during blooms, evidence points to an acidification of the oceans (pH falls) during the coming decades as anthropogenic CO2 derived from human activity dissolves in the surface ocean. The impact upon the growth of phytoplankton, nutrient partitioning, and their capacity to acclimate to a relatively acidic environment is completely unknown. The implications for the marine environment and the services that it provides warrants urgent investigation. This project, conducted jointly between Swansea University and Plymouth Marine Laboratory, will see cultures of representative phytoplankton subjected to different conditions (nutrient availability, pH) representing current day and future (acidified oceanic) situations. Data describing changes in growth and activity of the organisms will support the construction and testing of mathematical models. The results will thence be incorporated into ecosystem models that will examine the implications for marine productivity and biogeochemistry of the improved description of phytoplanktonic activity, and of ocean acidification for the UK shelf seas.