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营养丰富的状态转变为其他季节营养贫乏的状态。圣佩德罗海洋时间序列（SPOT）位于洛杉矶港和卡塔琳娜岛之间离岸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项目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）浓度的上升和表面pH值的降低，了解沿海水域初级生产的营养控制和沿海生态系统对CO2的封存能力至关重要。该项目将在两个季节周期内检查SPOT的初级生产速率、与初级生产相关的氮吸收以及铵氧化为硝酸盐（硝化）。它还将通过培训南加州大学和马里兰大学的本科生和研究生，为开发海洋科学方面的人力资源作出贡献。研究人员参与教育推广活动（例如通过海洋科学教育卓越计划中心），并将在这些报告中纳入本研究的发现。该项目将调查SPOT的初级生产和氮(N)动态，并具体实施新生产的分析。新的生产概念模型是生物海洋学中的一个强有力的组织原则，并提供了一种限制可能出口或从系统中“隔离”的初级产品数量的手段。尽管对氮的新形式和再生形式的定义进行了限定，但该概念在很大程度上被狭义地应用，指定硝酸盐为新氮的主要形式，铵为主要的再循环形式。越来越多的证据表明，这些定义可能需要扩展。固氮有时是新氮的重要来源；同样，溶解有机氮的形式（如尿素）可能对循环生产有重大贡献，但参与这些转化的具体生物仍不确定。上层水柱的硝化作用也可能损害新氮和再生氮的严格定义。科学家们现在可以更深入地探索新氮和再生氮的生产，并使用新的分子技术直接确定这些过程的主要因素。该项目将量化沿海生态系统中的新产品和再生产品，阐明所涉及的主要化合物。初级生产速率、硝态氮、铵态氮和尿素同化速率、氮固定速率和硝化速率将在上层水柱与每月的SPOT巡航一起确定。同时，两种稳定同位素探测（SIP）方法（用于硝酸盐、铵和尿素吸收的常规SIP与高通量测序和基于芯片的Chip-SIP用于N2固定）将用于直接确定参与这些过程的主要因素，以及13c -尿素进入硝化生物质的吸收。以下两个假设将被检验：1。固氮是支持出口生产的南加州沿海水域新氮的重要来源。2. 溶解形式的有机氮，特别是尿素，可以作为硝化的底物，对再生生产有很大贡献。

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.