Biological characterization of the nitrogen-fixing Rhizosolenia-Richelia symbiosis

固氮为低营养海洋地区提供了一个重要的新氮输入。过去二十年的研究工作突出了毛菌素的作用。最近，球藻蓝藻的作用以及丝状蓝藻胞内Richelia与硅藻（rhizzosolenia和Hemiaulus）的共生关系受到了关注。人们对这些硅藻-重氮营养体的生长速率、营养需求、化学成分或环境耐受性知之甚少。然而，很明显，在某些海洋中，dda在数值上很重要，并且可以在调节新的氮输入方面发挥主要作用。最近的模型已经确定了需要特定物种的参数，但这些参数对于dda来说是缺乏的。特别是，需要对温度相关的特性进行量化，以便应用于全球变暖情景。根治菌-黎塞菌DDA的实验室研究现在是可能的，因为这种关联的可重复培养。这项为期四年的研究计划将量化温度和盐度对生长速率和nb2b固定速率的影响。它将探讨硅酸盐和磷酸盐（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nb2b固定中的作用。沉积圈闭和沉积记录中DDAs的大量聚集表明DDAs是深度的重要载体。相对于Trichodesmium而言，潜在的高下沉速率允许新N的快速输出和c的固存。这项工作将量化磷酸盐和硅酸盐限制生长条件下的沉降速率，并提供由于下沉造成的潜在损失的初步估计。该项目将提供DDA的第一个广泛特征，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，以量化已知在那里发生的dda的比率和局限性。工作将侧重于利用DDA生长速率和NB2B固定来研究对磷添加的响应。同时进行的研究使用净拖将量化在自然条件下根瘤菌-黎塞菌的生长速度。DDA水华是通过硅藻宿主的大量沉积快速从光带去除C和N的潜在手段。沉积物中的硅藻残留物表明这是沉积沉积的重要载体。本研究中的自动机工作将为解释此类事件如何发生提供重要信息。此外，耐温性研究将为了解DDA如何应对海洋变暖提供有用的数据。总的来说，共生是生物学中一个引人入胜的部分，这项工作将通过提供海洋dda生物学的第一个系统研究来丰富生物学文献。这些数据将为研究深海固氮和碳通量的生物学和古海洋学模型提供重要的输入数据。这个项目将支持两名研究生，并作为几个每周广播节目和公共研讨会系列演讲的基础。

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.