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（OMZ）正在增加。脱氧的扩展具有显著的生态后果，并通过生物介导的碳和氮循环变化影响全球气候。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至关重要。本项目研究了一组重要的真核单细胞生物--自由漂浮有孔虫在OMZ内生存的策略。一个特别的焦点是水柱中的有孔虫是否可以像海底的有孔虫物种一样呼吸氮，并对全球氮循环做出重大贡献。该项目支持两名职业生涯初期的女科学家，其中一名来自地球科学领域代表性不足的群体，并在北卡罗来纳州州立大学为一名研究生和几名本科生提供海上和实验室培训。此外，科学推广活动还包括与爱荷华州大学教授合作举办的科学艺术展览，以及为马萨诸塞州法尔茅斯的高中新生提供的多媒体多感官教学模块，分享有关生活在缺氧环境中的海洋物种的项目。该项目的总体目标是阐明浮游有孔虫在缺氧和缺氧环境中生存的生物策略在大洋中。该项目测试三个相互关联的假设：1。OMZ栖息的浮游有孔虫能够进行反硝化作用; 2.反硝化作用在南极有孔虫中广泛存在，在OMZ附属类群之内和之外; 3.浮游有孔虫能够进行硝酸盐呼吸，而不管宏观环境的氧浓度。从深度分层网拖（MOCNESS）沿着南北样带以上和东北太平洋OMZ内的样品被用来量化的丰度和分布的南极有孔虫跨越氧气梯度，并了解南极有孔虫如何容忍低氧环境。被认为生活在可变氧环境中的有孔虫物种的元转录组学分析被用来测试反硝化途径的存在。额外的船上培养的个人允许直接测试反硝化作用。这些分析正在评估反硝化潜力在浮游有孔虫中的分布有多广，以及在什么样的氧浓度下有孔虫可能会活跃地反硝化。此外，对保存的有孔虫的分析正在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，从而揭示其他潜在的生存策略（即，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。

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.