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

越来越多的人认识到，太平洋和大西洋的低营养地表水的自养群落可能是磷有限或紧张的（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，在这些系统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，可能使浮游植物和细菌难以获得生长所需的足够磷。浮游植物应对砷的一种机制是砷酸盐还原为亚砷酸盐，甲基化为一甲基和二甲基砷。在磷胁迫或磷限制下，浮游植物对砷胁迫的不同解毒能力可能会影响自养群落的结构，这在沿海水域已得到证实。因此，对初级生产和自养群落进行简单营养限制控制的旧范式可能需要被更复杂的范式所取代，在这种范式中，非必需但具有生物活性的元素（如as）也可能被证明深刻影响自养群落。为了确定这两种元素的生物地球化学之间的联系，以及As（及其与P的相互作用）在海洋自养群落调节中的作用，史密森学会和斯基德韦海洋研究所的科学家将使用培养的分离物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P胁迫整合的周期。本研究还将探索亚砷酸盐和甲基砷作为磷胁迫或限制在各种时空尺度上的示踪剂的发展。一组代表浮游植物群落几个重要成员的培养分离物（原绿球藻、聚藻球菌、较大的真核生物）将进行As/P/N比对As抗性的测试。这些培养物将保持非常稀释，营养浓度低，因此每个物种的生长将使用流式细胞术进行跟踪。本研究的另一个目的是证实蓝藻比真核生物更能抵抗高砷磷比的假设。这项研究的更广泛的影响包括促进对一个潜在的关键因素的更好理解，即浮游植物和细菌必须在开放海洋的大片区域内竞争以获得一种有限的营养物质——磷。此外，pi将指导少数民族本科生和培训研究生培养精致的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.