DOP Utilization in the Sargasso Sea: Quantifying Taxon-specific Rates of Hydrolysis and Uptake

海洋浮游植物通过光合作用吸收二氧化碳，并将由此产生的有机碳输出到深海，这构成了一个能够从大气中提取全球大量二氧化碳的“生物泵”。越来越多的证据表明，两个较大的亚热带海洋环流--西热带/亚热带大西洋(马尾藻海)和北太平洋亚热带环流--的初级生产量可能受磷有效性的控制。在这些环境中，无机磷(SRP)浓度极低，在一些地点为亚纳米摩尔，无机N：P比值远远超过典型的Redfield比值。在这些SRP低的地区，溶解有机磷(DOP)可能有助于满足生物磷需求：在马尾藻海收集的数据显示，夏季层结期间DOP库存下降了30%。初级生产者对DOP的水解和同化很可能依赖于浮游植物的生理，并且在不同类群之间以及在空间和时间上存在很大的差异。研究人员假设，尽管周转时间很快，但如果不利用DOP池中的额外磷，BATS长期较低的季节性不变的SRP浓度无法支持测得的初级生产率。此外，微生物类群之间固有的生理差异是DOP利用率在时间和空间上变异的一个重要来源，这种差异既不被理解也不受限制。PIs建议使用成熟的分类单元特定方法来：量化马尾藻海DOP水解的时间和空间变异性；量化特定分类单元SRP和DOP吸收速率的时间和空间变异性；量化整个群落的总P吸收速率以及SRP和复合DOP吸收和再生速率；确定DOP水解和同化速率的调节因素；以及评估DOP在支持马尾藻海初级生产方面的作用。在广泛的范围内了解海洋生态系统的功能是重要的。海洋浮游植物通过光合作用吸收二氧化碳，并将由此产生的有机碳输出到深海，这是一个从全球范围内从大气中去除大量二氧化碳的“生物泵”。该项目将有助于限制对马尾藻海海洋生物泵强度的预测。如果溶解的有机磷支持马尾藻海初级生产力的很大一部分，那么中央海洋生物代谢过程的多样性在全球碳循环中发挥的作用比目前认识到的更大。研究人员每年将资助至少三名本科生研究人员，以及两名研究生。该项目产生的数据将用于调查员教授的课程的以问题为基础的学习模块，课程将提交给适当的数字存储库，如www.dlese.org。

Photosynthetic uptake of CO2 by oceanic phytoplankton and the export of the resulting organic carbon to the deep sea comprise a "biological pump" capable of extracting globally significant amounts of CO2 from the atmosphere. Mounting evidence suggests that primary production in two of the larger subtropical ocean gyres, the Western Tropical/Subtropical Atlantic (Sargasso Sea) and the North Pacific Subtropical Gyre, may be controlled by phosphorus availability. There are vanishingly low inorganic phosphorus (SRP) concentrations, sub-nanomolar in some locales, and ratios of inorganic N:P greatly exceed the canonical Redfield Ratio in these environments. In these low SRP regions dissolved organic phosphorus (DOP) may help meet biological phosphorus demand: data collected in the Sargasso Sea shows a 30% decline in DOP inventories during summer stratification. The hydrolysis and assimilation of DOP by primary producers is likely dependent on phytoplankton physiology, and highly variable between taxa, and through space and time. The investigators hypothesize that despite rapid turnover times, chronically low and seasonally invariant SRP concentrations at BATS cannot support measured rates of primary production without utilization of additional P from the DOP pool. Furthermore, inherent physiological differences among microbial taxa represent a significant source of temporal and spatial variability in DOP utilization rates that is yet neither understood nor constrained. The PIs propose to use proven taxon-specific methodologies to: quantify temporal and spatial variability in DOP hydrolysis in the Sargasso Sea; quantify temporal and spatial variability in taxon-specific SRP and DOP uptake rates; quantify whole-community total P uptake rates as well as SRP and model compound DOP uptake and regeneration rates; identify factors regulating rates of DOP hydrolysis and assimilation; and evaluate the role of DOP in supporting primary production in the Sargasso Sea. An understanding of ocean ecosystem function is important on a broad scale. Photosynthetic uptake of CO2 by oceanic phytoplankton and the export of the resulting organic carbon to the deep ocean are a "biological pump" that removes globally significant amounts of CO2 from the atmosphere. This project will help to constrain predictions of the strength of the oceanic biological pump in the Sargasso Sea. If dissolved organic phosphorus supports a significant fraction of primary production in the Sargasso Sea, then diversity in biological metabolic processes in the central oceans plays a greater role in the global carbon cycle than is presently recognized. The investigators will sponsor a minimum of three undergraduate researchers each year, as well as two graduate students. Data generated from the project will be used in problem-based learning modules for courses taught by the investigators, and the curriculum will be submitted to an appropriate digital repository such as www.dlese.org.