Biological characterization of the nitrogen-fixing Rhizosolenia-Richelia symbiosis

固氮作用为贫营养的海洋区域提供了新氮的关键输入。过去二十年的工作突出了束毛藻的作用。最近，球状蓝藻的作用以及丝状蓝藻Richelia intracellularis与硅藻（Ringulasolenia和Hemiaulus）的共生关系受到了关注。很少有人知道的生长速率，营养需求，化学成分，或环境耐受性的这些固氮生物协会（DDAs）。然而，很明显，DDAs在某些海洋中具有重要的数值，并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异性参数的需要，但这些是缺乏的DDAs。特别是，温度依赖的属性需要量化的应用到全球变暖的情况。由于该协会的可再生培养，现在可以对Rackensolenia-Richelia DDA进行实验室研究。这项为期四年的研究计划将量化温度和盐度对生长率和NB 2B固定率的影响。它将探索硅酸盐和磷酸盐（无机和有机）在控制生长速率，化学成分和NB 2B固定通过主机共生体相互作用的作用。大量积累的DDAs沉积物陷阱，以及在沉积记录表明DDAs是重要的矢量深度。相对于束毛藻，潜在的高下沉速率允许新N的快速输出和C的螯合。这项工作将量化磷酸盐和硅酸盐限制生长条件下的沉降速率，并提供对沉降造成的潜在损失的初步估计。该计划将提供DDA的第一个广泛表征，并为模型提供有价值的输入数据。实验室的数据将用于一对巡航到N。太平洋，以量化率和限制的DDAs已知发生在那里。工作将集中在响应磷添加使用DDA的增长率和NB 2B固定。使用网拖的同步研究将量化在自然条件下的龙葵Richelia的增长率。DDA水华是通过硅藻宿主的大量沉积从真光层快速去除C和N的潜在手段。沉积物中的硅藻遗骸表明这是沉积作用的重要载体。这项研究中的自体学工作将产生重要的信息来解释这些事件如何发生。此外，温度耐受性研究将产生有用的数据，以了解这种DDA如何应对海洋变暖。共生体是生物学的一个迷人的部分，一般来说，这项工作将丰富生物学文献提供了第一个系统的研究海洋DDAs的生物学。这些数据将为生物和古海洋学模型提供重要的输入数据，研究氮固定和碳流入深海。该计划将支持两名研究生，并作为几个每周广播节目和在公开研讨会系列讲座的基础。

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.