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

随着世界海洋含氧量的下降，无法维持生命的沿海地区(“死亡区”)和开放海洋的含氧量最低区(OMZ)正在增加。脱氧作用的扩大具有重大的生态后果，并通过生物中介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是至关重要的。这个项目调查了自由漂浮的有孔虫，一个重要的真核单细胞生物群体，在OMZ内生存所使用的策略。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一样呼吸氮气，并对全球氮循环做出重大贡献。该项目支持两名职业生涯早期的女科学家，包括一名来自地球科学界代表性不足的群体的女科学家，以及北卡罗来纳州立大学一名研究生和几名本科生的海上和实验室培训。此外，科学推广活动包括与爱荷华大学的一名教授合作举办的科学通过艺术展览，以及为马萨诸塞州法尔茅斯的高一学生提供的多媒体多感官教学模块，以分享该项目关于生活在缺氧环境中的海洋生物的各个方面。该项目的总体目标是阐明浮游有孔虫在中上层海洋的缺氧和缺氧环境中茁壮成长的生物学策略。该项目测试了三个相互关联的假设：1.生活在OMZ的浮游有孔虫能够进行反硝化作用；2.在OMZ附属分类群内外的浮游有孔虫中普遍存在反硝化作用；3.能够进行硝酸盐呼吸的浮游有孔虫，无论大环境中的氧浓度如何，都能进行反硝化作用。从东北太平洋OMZ上方和内部的南北断面采集的深度分层网状拖网(MOCNESS)样本被用来量化浮游有孔虫的丰度和跨氧梯度的分布，并了解浮游有孔虫如何耐受低氧环境。对被认为生活在不同氧气环境中的有孔虫物种进行了元转录分析，以测试是否存在反硝化途径。额外的船上培养的个体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情况，以及在什么氧浓度下有孔虫可以积极反硝化。此外，对保存下来的有孔虫的分析正在测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，以揭示其他潜在的生存策略(即共生)。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.