Collaborative Research: Oceanic diazotroph community structure and activities in a high carbon dioxide world

北太平洋亚热带环流(NPSG)是地球上最大的海洋生态系统，在全球碳循环中发挥着突出作用，并形成了重要的海洋生物多样性储藏库。固氮细菌(称为重氮菌)为NPSG的低营养水体提供了新的氮的主要来源，从而直接控制了碳循环。海洋对二氧化碳的吸收导致该生态系统海水中二氧化碳分压(PCO2)的长期变化。因此，了解碳系统的扰动如何影响海洋生物地球化学是一项重要而及时的工作。在这个项目中，研究人员将研究固定氮微生物的自然组合如何响应海水碳化学的扰动。实验室和实地实验将在每月对固定微生物丰度的氮气的活动和丰度进行时间序列测量的情况下进行。总而言之，该项目将深入了解氮气固定微生物生理对二氧化碳变化的依赖。这项研究的广泛目标是：(1)量化海水二氧化碳变化对海洋自然发生的固氮菌群落的生长和群落结构的反应和后果；(2)确定海水二氧化碳的变化为什么以及如何影响两种模式海洋固氮菌(毛藻和冠藻)的生长和碳获取策略；(3)量化阿罗哈站重固氮生物群落结构和活动的时间变异性。更广泛的影响包括对气候变化情景对海洋生物地球化学的潜在影响提供重要见解，这对微生物生态学家、气候变化科学家和生物地球化学家将是有价值的。此外，计划为本科生和研究生提供研究机会，重点是妇女和代表不足的群体参与科学。

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."The North Pacific Subtropical Gyre (NPSG) is the largest ocean ecosystem on Earth, playing a prominent role in global carbon cycling and forming an important reservoir of marine biodiversity. Nitrogen (N2) fixing bacteria (termed diazotrophs) provide a major source of new nitrogen to the oligotrophic waters of the NPSG, thereby exerting direct control on the carbon cycle. Oceanic uptake of CO2 causes long-term changes in the partial pressure of CO2 (pCO2) in the seawater of this ecosystem. Therefore, understanding how carbon system perturbations may influence ocean biogeochemistry is an important and timely undertaking.In this project, the investigators will examine how natural assemblages of N2 fixing microorganisms respond to perturbations in seawater carbon chemistry. Laboratory and field-based experiments will be placed in the context of monthly time series measurements on the activities and abundances of N2 fixing microorganism abundances. Together, the project will provide insight into the dependence of N2 fixing microorganism physiology on variations in CO2. The broad objectives of the research are: (1) Quantify the responses and consequences of changes in seawater pCO2 on the growth and community structure of naturally-occurring assemblages of ocean diazotrophs; (2) Identify why and how changes in seawater pCO2 influence the growth and carbon acquisition strategies of two model marine diazotrophs (Trichodesmium and Crocosphaera); and (3) Quantify temporal variability in diazotroph community structure and activities at Station ALOHA. The broader impacts include providing important insights into potential influences of climate change scenarios on ocean biogeochemistry which will be valuable to microbial ecologists, climate change scientists, and biogeochemists. In addition, research opportunities for both undergraduate and graduate students are planned with an emphasis on participation of women and underrepresented groups in science.