Collaborative Research: Assessing denitrification and other strategies for planktic foraminiferal survival under dysoxic conditions

随着世界海洋中氧气含量的下降，无法维持生命的沿海地区（“死亡区”）和开放海洋氧气最低区（OMZs）正在增加。缺氧扩展通过生物介导的碳氮循环变化对全球气候产生重要的生态影响。因此，了解耐受极低氧环境的生物的生存策略和生物地球化学贡献是至关重要的。该项目研究了自由漂浮的有孔虫（一种重要的真核单细胞生物）在OMZ中生存的策略。一个特别的焦点是水柱中的有孔虫是否能像海底的有孔虫一样呼吸氮，并对全球氮循环做出重大贡献。该项目支持两名早期职业女性科学家，其中一名来自地球科学领域代表性不足的群体，并为北卡罗来纳州立大学的一名研究生和几名本科生提供海上和实验室培训。此外，科学拓展包括与爱荷华大学教授合作的科学艺术展览，以及为马萨诸塞州法尔茅斯的一年级高中学生提供多媒体多感官教学模块，以分享有关生活在缺氧环境中的海洋物种的项目方面。该项目的总体目标是阐明浮游有孔虫在远洋缺氧和缺氧环境中茁壮成长的生物策略。该项目测试了三个相互关联的假设：栖息于omz的浮游有孔虫具有反硝化作用；2. 反硝化作用在浮游有孔虫中广泛存在，在omz附属分类群内外；3. 浮游有孔虫能够进行硝酸盐呼吸，而不管宏观环境中的氧浓度如何。本文利用东北太平洋OMZ上方和内部沿南北样带的深度分层网带（MOCNESS）样本，量化了浮游有孔虫在氧梯度上的丰度和分布，并了解了浮游有孔虫如何耐受低氧环境。对生活在可变氧环境中的有孔虫物种的超转录组学分析被用来测试反硝化途径的存在。额外的船上个人孵育允许直接测试反硝化。这些分析正在评估浮游有孔虫的反硝化潜力有多广泛，以及在什么氧浓度下有孔虫可能积极反硝化。此外，对保存的有孔虫进行分析，确定细胞质硝酸盐和氮同位素含量，并进行细胞学研究，以阐明超微结构，揭示其他潜在的生存策略（即共生）。该奖项反映了美国国家科学基金会的法定使命，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。

As the oxygen levels in the world’s oceans are decreasing, the coastal areas that cannot support life (‘dead zones’) and open ocean oxygen minimum zones (OMZs) are increasing. The expansion of deoxygenation has significant ecological consequences and impacts global climate through biologically-mediated carbon and nitrogen cycling changes. Understanding the survival strategies and biogeochemical contributions of organisms that tolerate very low-oxygen environments is thus critical. This project investigates the strategies that free-floating foraminifera, an important group of eukaryotic single-celled organisms, use to survive within the OMZ. A particular focus is whether foraminifera in the water column can respire nitrogen like foraminifera species within the ocean floor and contribute significantly to global nitrogen cycling. This project supports two early-career female scientists, including one from an underrepresented group in geosciences, and at sea and laboratory training for one graduate student and several undergraduates at North Carolina State University. In addition, science outreach includes a Science-through-Art exhibition in collaboration with a professor at the University of Iowa and a multimedia multi-sensory teaching module for freshman high school students in Falmouth, MA, to share aspects of the project about marine species living in deoxygenated settings.The overall goal of this project is to elucidate the biological strategies planktic foraminifera use to thrive in dysoxic and anoxic environments in the pelagic ocean. The project tests three interrelated hypotheses: 1. OMZ-dwelling planktic foraminifera are capable of performing denitrification; 2. Denitrification is widespread among planktic foraminifera, within and beyond OMZ-affiliated taxa; 3. Planktic foraminifera capable of nitrate respiration do so regardless of macroenvironmental oxygen concentrations. Samples from depth-stratified net tows (MOCNESS) along a north-south transect above and within the Northeastern Pacific OMZ are used to quantify the abundance and distribution of planktic foraminifera across oxygen gradients and to understand how planktic foraminifera tolerate low-oxygen environments. Metatranscriptomic analyses of foraminifera species thought to live in variable oxygen environments are used to test for the presence of denitrification pathways. Additional shipboard incubations of individuals allow direct testing for denitrification. These analyses are assessing how widespread denitrification potential is among planktic foraminifera and under what oxygen concentrations foraminifera may actively denitrify. Additionally, analysis of preserved foraminifera are determining cytoplasm nitrate and nitrogen isotope content and cytological studies to elucidate ultrastructure to reveal other potential survival strategies (i.e., symbiosis).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.