Collaborative Research: New Approaches to New Production

沿海海洋生态系统具有季节性动态和高生产力。浮游植物种群从春季的营养充足状态转变为其他季节的营养贫乏状态。圣佩德罗海洋时间序列（SPOT）位于洛杉矶港和卡塔利纳岛之间的近海17公里处，是一个具有代表性和可访问的模型海岸系统，具有定期采样和大量相关观测档案。自2000年以来，SPOT计划已经对微生物种群的动态，多样性和生产力进行了编目。随着二氧化碳（CO2）浓度的上升，导致表面pH值的下降，这是至关重要的是要了解营养控制的初级生产在沿海沃茨和沿海生态系统的能力，以封存CO2。 该项目将在SPOT研究两个季节周期内的初级生产率、与初级生产有关的氮吸收率以及铵氧化成硝酸盐（硝化作用）。它还将通过培训南加州大学和马里兰州大学的本科生和研究生，促进海洋科学人力资源的开发。 研究人员参加教育推广活动（例如通过海洋科学教育卓越计划中心），并将把这项研究的结果纳入这些演示文稿中。该项目将调查SPOT的初级生产和氮（N）动态，并特别实施新生产的分析。新的生产概念模式一直是生物海洋学的一个强有力的组织原则，并提供了一种手段来限制可能从系统中输出或“隔离”的初级生产量。尽管对最初阐述的新的和再生形式的N的定义有限制，但在大多数情况下，这一概念被狭义地应用，指定硝酸盐为新N的主要形式，铵为主要的再循环形式。越来越多的证据表明，这些定义可能值得扩大。N固定有时是新N的主要来源;类似地，溶解的有机N的形式（例如，尿素）可能对循环生产做出重大贡献，但参与这些转化的具体生物仍不确定。 上层水体中的硝化作用也可能影响新氮和循环氮的严格定义。科学家现在可以更深入地探索新的和再生的生产，并使用新的分子技术直接识别这些过程的主要因素。该项目将量化沿海生态系统中新的和再生的生产，阐明所涉及的主要化合物。初级生产率，硝酸盐，铵和尿素同化，N2固定，硝化作用将在上层水柱与每月SPOT巡航一致。串联，两个稳定同位素探测（SIP）的方法（传统的SIP的硝酸盐，铵和尿素的吸收耦合到高通量测序和基于芯片的芯片SIP的N2固定）将用于直接识别参与这些过程中的主要代理商，沿着的13 C-尿素的吸收到硝化生物质。将检验以下两个假设：1。固氮是南加州沿海沃茨新氮的重要来源，支持出口生产。2.溶解有机氮的形式，特别是尿素，可以是硝化作用的底物，并大大有助于再生生产。

Coastal marine ecosystems are seasonally dynamic and highly productive. Phytoplankton populations shift from nutrient replete conditions in the spring to nutrient poor conditions in other seasons. The San Pedro Ocean Time-series (SPOT), located 17 km offshore between Los Angeles Harbor and Catalina Island, is a representative and accessible model coastal system with regular sampling and a substantial archive of relevant observations. The SPOT program has cataloged the dynamics, diversity, and productivity of microbial populations since 2000. With rising carbon dioxide (CO2) concentrations and resulting decreases in surface pH, it is critically important to understand the nutrient controls on primary production in coastal waters and the capacity of coastal ecosystems to sequester CO2. This project will examine rates of primary production, nitrogen uptake associated with primary production, and the oxidation of ammonium to nitrate (nitrification), at SPOT over two seasonal cycles. It will also contribute to the development of human resources in the marine sciences through the training of undergraduate and graduate students at the University of Southern California and the University of Maryland. The researchers participate in education outreach activities (e.g. through the Centers for Ocean Sciences Education Excellence programs), and will incorporate findings from this study in those presentations.This project will investigate primary production and nitrogen (N) dynamics at SPOT and specifically implement an analysis of new production. The new production conceptual model has been a powerful organizing principle in biological oceanography and provides a means to constrain the amount of primary production that may be exported or "sequestered" from the system. Despite qualifications to the definitions of new and regenerated forms of N as originally articulated, the concept has, for the most part, been narrowly applied, specifying nitrate as the primary form of new N, and ammonium as the predominant recycled form. Evidence continues to accumulate that these definitions may warrant expansion. N fixation can be at times a substantial source of new N; similarly, forms of dissolved organic N (e.g., urea) may contribute significantly to recycled production, but the specific organisms taking part in these transformations are still uncertain. Nitrification in the upper water column may also compromise the strict definitions of new and recycled N. Scientists can now probe more deeply into new and regenerated production, and directly identify major agents of these processes using new molecular techniques. This project will quantify new and regenerated production in a coastal ecosystem, illuminating the predominant compounds involved. Rates of primary production, nitrate, ammonium and urea assimilation, N2 fixation, and nitrification will be determined in the upper water column in concert with monthly SPOT cruises. In tandem, two stable isotope probing (SIP) approaches (conventional SIP for nitrate, ammonium and urea uptake coupled to high throughput sequencing and microarray based Chip-SIP for N2 fixation) will be used to directly identify the major agents involved in these processes, along with the uptake of 13C-urea into nitrifier biomass. The following two hypotheses will be tested:1. N2 fixation is a substantial source of new N in coastal waters of Southern California supporting export production. 2. Forms of dissolved organic N, and specifically urea, can be substrates for nitrification and contribute substantially to regenerated production.