Collaborative Research: New Approaches to New Production

沿海海洋生态系统是季节性动态的，生产力很高。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不良状态。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离岸17公里处，是一个具有代表性的可利用的模式沿海系统，定期采样并有大量相关观测记录。Spot计划自2000年以来一直对微生物种群的动态、多样性和生产力进行编目。随着二氧化碳(CO2)浓度的上升和由此导致的表面pH的下降，了解营养物质对沿海水域初级生产力的控制以及沿海生态系统封存二氧化碳的能力至关重要。该项目将在两个季节周期内现场考察初级生产量的速率、与初级生产量相关的氮素吸收以及氨氧化为硝酸盐(硝化作用)。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)，并将把这项研究的结果纳入那些报告中。该项目将调查现场的初级生产和氮(N)动态，并具体实施对新生产的分析。新的生产概念模型已成为生物海洋学中一项强有力的组织原则，并提供了一种手段来限制可能从该系统输出或“隔离”的初级生产量。尽管对最初阐明的新的和再生的N的定义有限制，但这个概念在很大程度上得到了狭隘的应用，指定硝酸盐为新N的主要形式，将铵指定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。固氮有时可能是新氮的重要来源；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，但参与这些转化的特定生物仍不确定。上层水柱中的硝化作用也可能危及对新的和回收的N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确定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，阐明涉及的主要化合物。初级生产力、硝酸盐、铵和尿素的同化、氮气固定和硝化作用的速率将在上层水柱中与每月的现场巡航相一致地确定。同时，两种稳定同位素探测(SIP)方法(用于硝酸盐、氨氮和尿素吸收的常规稳定同位素探测与高通量测序相结合的传统稳定同位素探测方法和用于氮气固定的基于芯片的稳定同位素探测方法)将被用来直接识别这些过程中涉及的主要制剂，以及13C-尿素被硝化菌生物量吸收的情况。将检验以下两个假设：1.氮固定是南加州沿海水域新氮的重要来源，支持出口生产。2.各种形式的溶解有机氮，特别是尿素，可以作为硝化作用的基质，并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.