COLLABORATIVE RESEARCH: Quantifying the effects of variable light and iron on the nitrate assimilation isotope effect of phytoplankton

合作研究：量化可变光和铁对浮游植物硝酸盐同化同位素效应的影响

• 批准号: 2406821
• 负责人: Sven Kranz
• 金额: $ 76.44万
• 依托单位: William Marsh Rice University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-10-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2406821&HistoricalAwards=false
• 关键词: COLLABORATIVE; RESEARCH; Quantifying; effects; variable

Phytoplankton are microscopic, single-celled organisms that play an important role in the Earth?s ecosystems, elemental cycles, and climate. These organisms, which live in surface ocean waters, require sunlight and nutrients to grow and reproduce. In the oceans around Antarctica, nitrate (NO3-) as a nutrient source of nitrogen (N) is usually abundant while the nutrient iron is often sparse. Light availability also changes from complete darkness to 24 hours of constant sunlight, as well as from low light deeper in the water column to high, stressful light at the ocean surface. As a consequence, the phytoplankton in the Southern Ocean often live in a suboptimal environment in which conditions for growth are frequently changing. Scientists understand that nutrient supply and light availability affect these organisms and that these organisms, in turn, can alter the chemical composition of the seawater. For example, nitrate can occur in different forms, including a lighter (14N) and heavier (15N) form of NO3-, depending on which stable isotope of N is present in the molecule. Phytoplankton prefer to use the lighter isotope during uptake and incorporation into biomass, though the ratio of 15N/14N used by phytoplankton has been shown to vary depending on environmental conditions. Notably, the isotope ratio used by phytoplankton is recorded in sediments and can be used to determine both the historic composition of ocean waters and the productivity of phytoplankton. This project will test the hypothesis that enhanced light and/or iron stress change the isotopic ratios of water column nitrate- in specific ways. A combination of laboratory culture and field experiments will be conducted. Cultures of important Southern Ocean phytoplankton species will be grown under environmentally-relevant light and iron conditions where ratio of 15N/14N used by phytoplankton, physiological changes, and molecular markers of iron and light stress and nitrate assimilation will be measured. Similar measurements will be done in shipboard experiments on a cruise in the Southern Ocean with South African colleagues. These data will increase our understanding of past and present productivity in the Southern Ocean, and how phytoplankton changed the chemical composition of the seawater. Undergraduates from underrepresented groups in the STEM field and graduate students from Florida State University and Old Dominion University as well as students from South Africa will collaborate on this project. The improved process understanding of the N isotope effect will be presented not only at scientific national and international conferences but also during local outreach events at local K12 schools.Interpretation of both modern water column nitrate (NO3-) isotopic ratio (d15N) measurements generated by GEOTRACES and other cruises, as well as metrics of paleo-nutrient utilization, depend upon a mechanistic understanding of the degree to which NO3- assimilation by phytoplankton discriminates against the heavier isotope, 15NO3- (NO3- assimilation epsilon). We currently lack the ability to predict how iron and light stress impacts the NO3- assimilation epsilon. The proposed work will test the hypothesis that enhanced light and/or iron stress elevates the epsilon for NO3-assimilation. This hypothesis will be tested by a combination of laboratory culture work and field work on a cruise of opportunity in the Southern Ocean. Mesocosm experiments will include both increasing and alleviating light and/or iron stress on monoclonal phytoplankton cultures and in natural phytoplankton communities while measuring the response of the NO3- assimilation epsilon. Water column samples will be collected on the cruise for analysis of dissolved and size-fractionated particulate N concentration and d15N, as well as phytoplankton community composition, photophysiology and gene expression markers of iron and light stress and NO3- assimilation. In particular, the expression of iron and light stress markers will be used to evaluate the relative contribution of iron and light stress to field-based estimates of the NO3-- assimilation epsilon. The results from these field measurements, together with lab-based culture studies, will be used to constrain the range of the epsilon for NO3- assimilation under environmentally-relevant light and iron conditions, including the potential alleviation of iron stress as has been hypothesized to have occurred during the last glacial maximum (a.k.a. the Martin hypothesis).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.

浮游植物是微观的单细胞生物，在地球生态系统，元素周期和气候中起着重要作用。这些生物存在于地表海水中的生物需要阳光和养分生长和繁殖。在南极洲周围的海洋中，硝酸盐（NO3-）作为氮（N）的营养来源通常很丰富，而营养铁通常很少。光的可用性也从完整的黑暗变为24小时的恒定阳光，以及从水柱中的低光到海面的高而压力的光线。结果，南大洋的浮游植物经常生活在次优的环境中，在这种环境中，生长经常发生变化。科学家了解到，养分供应和光的可用性会影响这些生物，而这些生物反过来可以改变海水的化学成分。例如，硝酸盐可以以不同的形式发生，包括较轻（14n）和较重的NO3-形式，具体取决于分子中的N稳定同位素。浮游植物在摄取过程中更喜欢使用较轻的同位素并掺入生物质中，尽管浮游植物使用的15N/14N的比例已根据环境条件而变化。值得注意的是，浮游植物使用的同位素比在沉积物中记录在沉积物中，可用于确定海水的历史成分和浮游植物的生产力。该项目将检验以下假设，即增强的光和/或铁应力以特定方式改变了硝酸盐柱的同位素比。将进行实验室培养和现场实验的结合。重要的南大洋浮游植物物种的培养物将在与环境相关的光线和铁条件下生长，其中浮游植物的比例将浮游植物，生理变化，生理变化以及铁和轻应激和硝酸盐同化的分子标记。在南非同事的南大洋巡游中，将在船上实验中进行类似的测量。这些数据将增加我们对南大洋过去和现在的生产力的理解，以及浮游植物如何改变海水的化学成分。来自STEM领域中代表性不足的团体的本科生，佛罗里达州立大学和老Dominion大学的研究生以及来自南非的学生将在该项目上合作。 The improved process understanding of the N isotope effect will be presented not only at scientific national and international conferences but also during local outreach events at local K12 schools.Interpretation of both modern water column nitrate (NO3-) isotopic ratio (d15N) measurements generated by GEOTRACES and other cruises, as well as metrics of paleo-nutrient utilization, depend upon a mechanistic understanding of the degree to which NO3-浮游植物同位素的同位素15no3-（NO3-同化Epsilon）歧视。目前，我们缺乏预测铁和光应力如何影响No3-同化Epsilon的能力。拟议的工作将检验以下假设，即增强光和/或铁应力可以提高epsilon以进行NO3辅助。这一假设将通过实验室文化工作和现场工作的结合在南大洋的机会巡游中进行检验。中验实验将包括对单克隆浮游植物培养物以及自然浮游植物群落的升高和减轻铁应激，同时测量NO3-同化Epsilon的反应。水柱样品将在巡航上收集，以分析溶解和尺寸分级的颗粒n浓度和D15N，以及浮游植物群落组成，光生理学和铁应力的基因表达标志物以及光应力和NO3-同化。特别是，铁和光应力标记的表达将用于评估铁和光应力对NO3-同化Epsilon的基于现场的估计值的相对贡献。这些现场测量结果以及基于实验室的培养研究的结果将用于限制在与环境相关的光线和铁条件下进行同化的Epsilon的范围，包括在最后的冰川最大化期间通过评估了Martin Mastion deals and Satte dere dere dere dere dery date dery deds niphation not and s feption notion and de every deds n s fection not and s。基金会的智力优点和更广泛的影响审查标准。