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

OCE-0526172越来越多的人认识到，太平洋和大西洋贫营养表层沃茨的自养生物群落可能受到磷的限制或压力（氮限制，但低磷浓度仍影响自养生物群落）。 一个潜在的加剧因素，磷限制是存在的砷酸盐（AsO 4 =），类似的磷酸盐（PO 4 =），这是目前在这些系统中相对恒定的浓度。 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的P。 浮游植物科普砷的一种机制是将砷酸盐还原为亚砷酸盐，并将甲基化为一甲基砷和二甲基砷。在磷胁迫或限制下，不同的浮游植物物种解毒砷（砷胁迫）的能力可能会影响自养群落的结构，已被证明在沿海沃茨。 因此，旧的模式简单的营养限制控制的初级生产和自养社区可能需要被取代的更复杂的模式，非必需的，但生物活性，元素，如作为也可能被证明深刻影响自养社区。为了确定这两种元素的地球化学之间的联系，以及As（以及与P的相互作用）在海洋沃茨中自养群落的调节中的作用，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。确切的化学和生物条件下，亚砷酸盐和甲基砷的生产率，其随后的降解速率和机制，将被量化，以计算其停留时间，因此期间的P应力集成。 本研究也将探讨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。 一套培养的菌株代表浮游植物群落（原绿球藻属，聚球藻属，较大的真核生物）的几个重要成员将进行测试作为作为一个功能的抗As/P/N比。这些培养物将保持非常稀释，营养浓度低，因此将使用流式细胞术跟踪每个物种的生长。 本研究的另一个目的是证实这一假设，蓝藻更耐高的As：P比比真核生物。 该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，即开放海洋大部分地区的浮游植物和细菌必须与之竞争以获得限制性营养素磷。 此外，PI将指导少数民族本科生，并培训研究生在培养微妙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.