Why so Little Planktonic Nitrogen Fixation in Estuaries-- Limitation by Trace Metals and Grazing?

为什么河口的浮游固氮如此之少——微量金属和放牧的限制？

• 批准号: 9307337
• 负责人: Robert Howarth
• 金额: $ 30万
• 依托单位: Cornell Univ - State: AWDS MADE PRIOR MAY 2010
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1993
• 资助国家: 美国
• 起止时间: 1993-11-01 至 1996-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9307337&HistoricalAwards=false
• 关键词: Why; so; Little; Planktonic; Nitrogen

9307337 Howarth In the temperate zone, primary production is limited by Nitrogen in many if not most estuaries and by Phosphorus in most lakes. One major reason for these difference is a difference in Nitrogen fixation by planktonic cyanobacteria (blue-green algae). In lakes, temporary shortages of Nitrogen relative to Phosphorus result in blooms of cyanobacteria which fix Nitrogen and help alleviate the shortage. This does not occur in most estuaries, where planktonic cyanobacteria capable of Nitrogen fixation are rare and rates of Nitrogen fixation low. The work proposed here addresses this difference with a series of mesocosm experiments using water from Narragansett Bay. The central hypothesis of the proposal is that low availability's of Iron and/or Molibdium in estuaries lead to slow growth rates of planktonic, Nitrogen-fixing cyanobacteria. This leaves the cyanobacteria vulnerable to consumption by generalized grazing animals, leading to low population numbers and rates of Nitrogen fixation. The hypothesis does not state that herbivores in estuaries specifically feed on cyanobacteria. Rather, it is hypothesized that estuarine ecosystems may contain high numbers of generalized grazers which are capable of feeding on fine cyanobacterial filaments and are likely to do so incidentally to their feeding on other particles when such filaments are present. Zooplankton, ctenophores, and a variety of bivalves (mussels, oysters, clams) are examples of such filter feeding animals common in estuaries which may fed on cyanobacterial filaments. With sufficiently high growth rates, cyanobacteria might bloom and fix Nitrogen even with high rates of grazing, as can happen in freshwater. Iron and/or Molibdium availability's are viewed as central to the growth rate of cyanobacteria based on previous research; the requirement for both in Nitrogen fixation is high. %%% Mesocosm experiments form the core of the proposed research. Estuarine water and plankton assemblages will be subje ct to different additions of Iron, Molibdium, and Phosphorus, and levels of grazing will be controlled by adding predators on herbivorous zooplankton. Silversides (Menidia beryllina) will likely be the predator used. Interactions of metal additions with the fish additions in replicated experiments are of particular interest. Response variables to be measured include rates of Nitrogen fixation, abundance's of cyanobacteria and heterocysts, composition of the zooplankton community, assimilation, of Molimdium, Sultan, and Iron, and concentrations of nutrients, Molibdium, and Iron. A recently published method using oxine to complex labile forms of Iron will be used to estimate Iron availability to phytoplankton. The proposed research should lead to a better understanding of the factors which exclude Nitrogen-fixing cyanobacteria from the plankton of most temperate estuaries and coastal seas, helping to cause Nitrogen limitation of net primary production in these systems. The research should also lead to a better understanding of the controls on Nitrogen fixation by plankton in lakes, and therefore on the maintenance of Phosphorus limitation even in lakes receiving nutrient loading with low Nitrogen:Phosphorus. Thus, the research relates to the practical issue of management strategies to control eutrophication in both estuaries and lakes.

9307337在温带区域中的Howarth，主要生产受到许多（如果不是大多数河口）和大多数湖泊中磷的限制。 造成这些差异的主要原因之一是浮游蓝细菌（蓝绿色藻类）固定氮的差异。 在湖泊中，氮相对于磷的暂时短缺导致蓝细菌的花朵固定氮并有助于减轻短缺。 这在大多数河口中都不会发生，因为浮游蓝细菌能够固定氮，并且氮固定的速率很低。 这里提出的工作通过使用Narragansett湾的水进行了一系列的中库实验来解决这种差异。 该提案的核心假设是河口中铁和/或小孢子的低可利用率导致浮游氮，固氮蓝细菌的生长缓慢。 这使蓝细菌容易受到普遍的放牧动物的消费，从而导致氮固定率较低。 该假设并不声明河口中的草食动物专门针对蓝细菌。 相反，假设河口生态系统可能包含大量的广义放牧者，这些放牧者能够以细蓝细菌的细丝为食，并且在存在此类细丝时可能会偶然地以其他颗粒为食。 浮游动物，灌木体和各种双壳类（贻贝，牡蛎，蛤）是这种过滤的例子，是河口中常见的滤食动物，这些动物可能会以蓝细菌丝的形式喂食。 随着足够高的生长速率，即使在淡水中可能发生的较高的放牧率，蓝细菌也可能会开花并固定氮。 基于先前的研究，铁和/或莫利氏的可用性被认为是蓝细菌生长速率的核心。两者在氮固定中的要求很高。 %% %%介体实验构成了拟议研究的核心。 河口水和浮游生物的组合将以不同的添加铁，小孢子和磷的添加，而放牧水平将通过在草食性浮游动物上添加捕食者来控制。 Silversides（Menidia Beryllina）可能是使用的捕食者。 在复制实验中，金属添加与鱼添加的相互作用尤其令人感兴趣。 要测量的响应变量包括氮固定速率，蓝细菌和杂环的丰度，浮游动物群落的组成，Molimdium，Sultan和Iron的同化，以及养分，Molibdium和铁的浓度。 最近发表的一种使用氧氨酸到复杂不稳的铁的方法将用于估计铁的可用性到浮游植物。 拟议的研究应更好地理解从大多数温带河口和沿海海域的浮游生物中排除固氮蓝细菌的因素，从而有助于在这些系统中对净初级生产限制氮。 这项研究还应更好地了解浮游生物在湖泊中对氮固定的控制，因此即使在接受低氮的营养负荷的湖泊中，磷限制的限制也是如此。 因此，该研究涉及控制河口和湖泊中富营养化的管理策略的实际问题。