Biological characterization of the nitrogen-fixing Rhizosolenia-Richelia symbiosis

固氮为营养稀少的海洋地区提供了新的氮素的关键输入。过去二十年的研究突出了毛霉菌的作用。最近，球状蓝藻的作用以及丝状蓝藻与硅藻(根霉属和半毛藻)的共生关系受到了关注。对这些硅藻-重氮菌群落(DDA)的生长速度、营养需求、化学成分或环境耐受性知之甚少。然而，很明显，在一些海洋中，DDA在数量上很重要，可以在调节新的氮输入方面发挥重要作用。最近的模型已经确定了物种特定参数的需要，但对于DDA来说，这些参数是缺乏的。特别是，依赖温度的特性需要量化才能应用于全球变暖的情景。由于这种组合的可重复培养，现在可以进行根霉-黎氏杆菌DDA的实验室研究。这项为期四年的研究计划将量化温度和盐度对生长率和NB2B固定率的影响。它将探索硅酸盐和磷酸盐(无机和有机)在通过宿主-共生体相互作用控制生长速度、化学成分和固定NB2B方面的作用。沉积圈闭和沉积记录中DDAS的大量积累表明，DDAS是深度的重要载体。相对于毛霉菌的潜在较高沉降率允许新N的快速出口和C的封存。这项工作将量化磷酸盐和硅酸盐限制生长条件下的沉降率，并提供沉淀物潜在损失的第一次估计。该计划将提供第一个对DDA的广泛描述，并为模型提供有价值的输入数据。实验室数据将用于两次前往北太平洋的巡航，以量化那里已知的DDA发生的速度和限制。工作将集中在使用DDA生长速率和NB2B固定对磷添加的响应上。同时使用净拖网的研究将量化自然条件下根霉-黎氏杆菌的生长速度。DDA水华是通过硅藻宿主的大量沉积迅速从真光层中去除C和N的潜在手段。沉积物中的硅藻遗骸表明这是沉积沉积的重要载体。这项研究中的自古学工作将提供重要的信息，以解释这种事件是如何发生的。此外，温度耐受性研究将产生有助于理解这种DDA如何应对海洋变暖的数据。更广泛的含义共生是生物学中令人着迷的部分，这项工作将通过提供对海洋DDA生物学的第一个系统研究来丰富生物学文献。这些数据将为考察深海固氮和碳通量的生物和古海洋学模型提供重要的输入数据。该计划将支持两名研究生，并作为几个每周广播节目的基础，以及在公共研讨会系列上的演讲。

Nitrogen-fixation provides a key input of new nitrogen into oligotrophic, oceanic regions. Work over the past two decades has highlighted the role of Trichodesmium. More recently, the role of coccoid cyanobacteria as well as symbiotic associations of the filamentous cyanobacteria Richelia intracellularis with species of diatoms (Rhizosolenia and Hemiaulus) has received attention. Little is known of the growth rates, nutrient needs, chemical composition, or environmental tolerances of these diatom-diazotroph associations (DDAs). However, it is clear that DDAs are numerically important in some oceans and can play a major role in mediating new nitrogen inputs. Recent models have identified the need for species-specific parameters, but these are lacking for DDAs. In particular, temperature dependent properties require quantification for application to global warming scenarios. Laboratory studies of the Rhizosolenia -Richelia DDA are now possible due to the reproducible cultivation of this association. This four-year research program will quantify temperature and salinity effects on growth rates and NB2B-fixation rates. It will explore the role of silicate and phosphate (inorganic and organic) in controlling growth rates, chemical composition and NB2B-fixation through host-symbiont interactions. The mass accumulation of the DDAs in sediment traps as well as in the sedimentary record suggest DDAs are important vectors to depth. The potentially high sinking rates relative to Trichodesmium permit rapid export of new N and sequestration of C. This work will quantify settling rates under conditions of phosphate and silicate-limited growth and provide the first estimates of potential losses due to sinking. This program will provide the first broad characterization of a DDA and provide valuable input data for models. The laboratory data will be used in a pair of cruises to the N. Pacific Ocean to quantify rates and limitations of DDAs known to occur there. Work will focus on the response to phosphorus additions using DDA growth rates and NB2B fixation. Concurrent studies using net tows will quantify growth rates of Rhizosolenia-Richelia under natural conditions. DDA blooms are potential means to remove C and N quickly from the euphotic zone via mass sedimentation of the diatom host. Diatom remains in sediments suggest this is an important vector for sedimentary deposition. The auteocological work in this study will produce information important for interpreting how such events can occur. In addition, temperature tolerance studies will yield data useful for understanding how this DDA could respond to warming oceans. Broader Implications Symbioses are a fascinating part of biology in general, and this work will enrich the biological literature by providing the first systematic study of the biology of marine DDAs. The data will provide important input data for biological and paleooceanographic models examining Nitrogen fixation and carbon flux into the deep sea. This program will support two graduate students, and serve as the basis for several weekly radio programs and talks at a public seminar series.