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

海洋浮游植物对二氧化碳的光合作用吸收和由此产生的有机碳向深海的出口构成了一个“生物泵”，能够从大气中提取全球大量的二氧化碳。越来越多的证据表明，两个较大的副热带海洋环流（西热带/副热带大西洋（马尾藻海）和北太平洋副热带环流）的初级生产可能受磷有效性的控制。在这些环境中，无机磷（SRP）浓度极低，在某些地方低于纳摩尔，无机氮：磷的比率大大超过了标准的红场比。在这些低SRP区域，溶解的有机磷（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，夏季分层期间，DOP库存下降了30%。初级生产者对DOP的水解和同化可能依赖于浮游植物的生理，并且在不同的分类群和时空中具有很大的差异。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P， BATS的SRP浓度长期较低且不随季节变化，则无法支持测量到的初级生产力。此外，微生物类群之间固有的生理差异是DOP利用率时空变异的重要来源，这一差异尚未被理解或限制。PIs建议使用经过验证的分类群特异性方法来量化马尾藻海DOP水解的时空变异性；量化不同分类单元SRP和DOP吸收率的时空变异性；量化全群落全磷吸收速率和SRP，并模拟复合DOP吸收速率和再生速率；确定调节DOP水解和同化速率的因素；并评价DOP对马尾藻海初级生产的支持作用。了解海洋生态系统的功能在广泛的范围内是很重要的。海洋浮游植物对二氧化碳的光合作用吸收以及由此产生的有机碳向深海的输出是一个“生物泵”，可以从大气中清除全球大量的二氧化碳。这个项目将有助于限制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的很大一部分，那么中部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要大。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研究人员讲授的课程的基于问题的学习模块，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.