Collaborative Research: Evaluating the contribution of small eukaryotes to nitrate-based new production in the North Pacific Subtropical Gyre

中纬度的亚热带海洋是“海洋沙漠”，那里的表层沃茨中营养物质相对较少。氮是一种重要的营养素，特别稀缺。氮在海洋中以硝酸盐或铵的形式存在。由于亚热带环流中的营养物质有限，那里的海藻或浮游植物生长缓慢。在水面以下较深的沃茨，有更多的营养物质。然而，夏季生活在表层沃茨的浮游植物如何获得深层沃茨的营养物质还不是很清楚。该奖项将调查浮游植物如何在北太平洋副热带环流（NPSG）的ALOHA站获得地下氮。浮游植物将按大小和色素成分分类。研究人员将对分类种群的稳定氮同位素比率进行测量，并确定浮游植物从哪里获得所需的营养物质，无论是来自地下的硝酸盐还是来自地表沃茨的铵。研究人员将使用元转录组学分析来研究不同浮游植物种群用于吸收所需氮的生理途径。元转录组学分析包括分析浮游生物转录的RNA序列，将该序列与记录的基因序列进行比较，并映射到记录的生理途径。研究人员将评估哪些分类群体使用硝酸盐和回收的氮源。他们将检验真核浮游植物主要利用硝酸盐而原核浮游植物主要利用循环氮源的假设。通过这些测量，研究人员将帮助社会预测气候对亚热带环流生产力的影响。该项目将支持两名研究生和一名博士后研究员进行实验室和船基研究。康涅狄格州的首席研究员（PI）格兰杰将通过AGU的桥梁合作伙伴计划吸引高中生并赞助来自代表性不足群体的研究生。北卡罗来纳州的PI Marchetti将赞助一名来自当地少数民族县的高中生实习。夏威夷的PI白色将通过土著海洋监测伙伴关系计划与夏威夷高中生接触，指导和教授基本的研究技能。该项目的研究人员将调查NPSG的ALOHA站的生产力驱动因素。他们将开发一种高灵敏度的天然丰度氮同位素分析方法（“过硫酸盐-还原剂”方法），以评估通过流式细胞术分选的浮游生物的分类学上不同的组分在多大程度上依赖于表层沃茨中的硝酸盐和还原氮源。我们还将查询浮游生物的生理氮代谢途径与元转录组学分析，以推断哪些分支是依赖于硝酸盐。我们将量化由硝酸盐驱动的初级生产的比例，以表征季节性趋势，并探索硝酸盐供应到真光层及其混合层的潜在机制。这里提出的工作将解决硝酸盐的相对贡献混合从海洋内部到表面生产站ALOHA，以更好地定义在NPSG的生物泵的季节性动态。我们将确定浮游生物群体，主要是硝酸盐为基础的生产和解决生态生理策略，赋予健身在一个严重的N-有限的环境。硝酸盐对总氮产量贡献的季节性趋势将在考虑事件水文学的情况下进行评估，以推断硝酸盐供应的潜在机制。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The subtropical oceans in the middle latitudes are “ocean deserts,” where there are relatively little nutrients in the surface waters. Nitrogen is an important nutrient that is particularly scarce. Nitrogen in the ocean occurs as nitrate or ammonium. As a result of limited nutrients in the subtropical gyres, marine algae or phytoplankton there grow slowly. In deeper waters below the surface, there are more nutrients. However, it is not well understood how phytoplankton living in surface waters in summer can access the nutrients in the deeper waters. This award will investigate how phytoplankton access subsurface nitrogen at Station ALOHA in the North Pacific Subtropical Gyre (NPSG). Phytoplankton will be sorted by size and pigment composition. The researchers will make measurements of the stable nitrogen isotope ratios of sorted populations and determine where phytoplankton are getting the needed nutrients, either nitrate from the subsurface or ammonium from the surface waters. The researchers will use metatranscriptomic analysis to investigate the physiological pathways that different phytoplankton populations use to take up the needed nitrogen. The metatranscriptomic analysis involves analyzing the RNA sequences transcribed by plankton, comparing the sequence to documented gene sequences and mapped to documented physiological pathways. The researchers will assess which taxonomic groups are using nitrate versus recycled sources of nitrogen. They will test the hypothesis that eukaryotic phytoplankton primarily use nitrate whereas prokaryotic phytoplankton mostly use recycled sources of nitrogen. With these measurements, the researchers will help the society anticipate climate impacts on the productivity of subtropical gyres. This project will support two graduate students and a post-doctoral researcher in laboratory and ship-based research. Principal Investigator (PI) Granger in Connecticut will engage high school students and sponsor graduate students from underrepresented groups via AGU’s Bridge Partner Program. PI Marchetti in North Carolina will sponsor the internship of a high school student from a local minority county. PI White in Hawaii will engage with Hawaiian high school students though the Indigenous Partnership for Ocean Monitoring program to mentor and teach essential research skills. The researchers of this project will investigate the drivers of productivity at station ALOHA in NPSG. They will exploit a high-sensitivity method for natural abundance N isotope analysis (the ‘persulphate-denitrifier’ method) to evaluate the extent to which taxonomically distinct components of the plankton sorted by flow cytometry rely on nitrate vs. reduced N sources in surface waters. We will also query physiological nitrogen pathways of the plankton with metatranscriptomic analysis to infer which clades are reliant on nitrate. We will quantify the fraction of primary production fueled by nitrate to characterize seasonal trends and explore potential mechanisms of nitrate supply to the euphotic zone and its mixed layer. The work proposed here will resolve the relative contribution of nitrate mixed from the ocean interior to surface production at station ALOHA, to better define seasonal dynamics of the biological pump in the NPSG. We will identify plankton groups that contribute dominantly to nitrate-based production and resolve eco-physiological strategies that confer fitness in a severely N-limited environment. Seasonal trends in the contributions of nitrate to total nitrogen production will be evaluated considering incident hydrography to infer potential mechanisms of nitrate supply.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.