Collaborative Research: Linking Arsenic Biogeochemistry, Phosphorus Limitation and Phytoplankton Dynamics in Oceanic Surface Waters

越来越多的人认识到，太平洋和大西洋低营养表层水域的自养群落可能是磷有限的或受到胁迫的(氮有限，但低磷浓度仍然影响自养群落)。磷限制的一个潜在加剧因素是砷酸盐(AsO4=)的存在，它是磷酸盐(PO4=)的类似物，在这些体系中以相对恒定的浓度存在。随着磷酸盐浓度的下降，As：P增加，可能会使浮游植物和细菌难以获得生长所需的足够磷。浮游植物用来对付AS的一种机制是将砷还原为亚砷酸盐，并将其甲基化为单甲基和二甲基砷。在磷胁迫或限制下，不同种类的浮游植物对砷的解毒能力不同(砷胁迫)可能会影响自养群落的结构，就像在沿海水域所证明的那样。因此，初级生产和自养群落的简单营养限制控制的旧模式可能需要被更复杂的模式取代，在这些模式中，非必要但具有生物活性的元素，如AS，也可能被证明对自养社区产生深远影响。为了确定这两种元素的生物地球化学之间的联系，以及As(以及与P的相互作用)在调节海洋水域自养群落中的作用，来自史密森研究所和斯基德韦海洋研究所的科学家将利用培养的分离株进行一系列实验室实验。将量化亚砷酸盐和甲基砷产生的确切化学和生物条件和速率，以及它们随后的降解速率和机制，以计算它们的停留时间，从而计算磷胁迫整合的时间。这项研究还将探索亚砷酸盐和甲基砷作为磷胁迫或限制的示踪剂在各种时间和空间尺度上的发展。一套代表浮游植物群落几个重要成员(原氯球菌、聚球藻、较大的真核生物)的培养分离株将作为AS/P/N比的函数进行AS抗性测试。这些培养物将保持非常稀薄，营养浓度较低，因此将使用流式细胞仪跟踪每个物种的生长。这项研究的另一个目的是证实蓝藻比真核物种更能抵抗高As：P比率的假说。这项研究的更广泛影响包括促进对一个潜在关键因素的更好理解，因为在公海的大片海域，浮游植物和细菌必须与之抗衡才能获得一种限制营养物质--磷。此外，PIS将指导少数族裔本科生，并培训研究生掌握培育精致海洋浮游生物的最新技术。

OCE-0526172There is a growing recognition that autotrophic communities of the oligotrophic surface waters of the Pacific and Atlantic Oceans may be phosphorus limited or stressed (nitrogen limited, but low phosphorus concentration still affects the autotroph community). A potentially exacerbating factor to P-limitation is the presence of arsenate (AsO4=), an analog of phosphate (PO4=), that is present in relatively constant concentrations in these systems. As phosphate concentrations decline, the As:P increases, potentially making it difficult for phytoplankton and bacteria to acquire sufficient P required for growth. One mechanism used by phytoplankton to cope with As is the reduction of arsenate to arsenite and methylation to monomethyl and dimethyl arsenic. Under P stress or limitation, the differing abilities of phytoplankton species to detoxify As (arsenic stress) may influence the structure of the autotrophic community, as has been demonstrated in coastal waters. Thus, older paradigms of simple nutrient limitation control of primary production and autotrophic communities may need to be replaced by more intricate paradigms where non-essential, but bioactive, elements such as As may also be shown to profoundly influence autotrophic communities. To define the linkage between the biogeochemistry of these two elements, and the role of As (and interactions with P) in the regulation of autotrophic communities in oceanic waters, scientists from the Smithsonian Institution and the Skidaway Institute of Oceanography will conduct a series of laboratory experiments using cultured isolates. The exact chemical and biological conditions and rates under which arsenite and methyl arsenic are produced, and their subsequent degradation rates and mechanisms, will be quantified to calculate their residence times, and hence periods of P stress integration. This research will also explore development of arsenite and methyl arsenic as tracers of phosphorus stress or limitation on a variety of temporal and spatial scales. A suite of cultured isolates representing several important members of the phytoplankton community (Prochlorococcus, Synechococcus, larger eukaryotes) will be tested for resistance to As as a function of the As/P/N ratio. These cultures will be kept very dilute, with low nutrient concentrations, so growth of each species will be followed using flow cytometry. Another aim of this study is to confirm the hypothesis that cyanobacteria are more resistant to high As:P ratios than eukaryotic species. The broader impacts of the research include fostering improved understanding of a potentially crucial factor, As, that phytoplankton and bacteria in large sectors of the open ocean must contend with to acquire a limiting nutrient, phosphorus. Additionally, the PIs will mentor minority undergraduate students and train graduate students in the latest techniques in culturing delicate marine plankton.