Exploring recalcitrant N regulation of free-living nitrogen fixation in terrestrial ecosystems

探索陆地生态系统自由固氮的顽固氮调节

• 批准号: 1547024
• 负责人: Maren Friesen
• 金额: $ 16.84万
• 依托单位: Michigan State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1547024&HistoricalAwards=false
• 关键词: Exploring; recalcitrant; regulation; free; living

Biological nitrogen fixation (BNF) is the conversion of atmospheric nitrogen gas to a form that is available for uptake by plants. This process, which is carried out by a type of microorganism known as diazatrophs, is responsible for 97% of new N inputs into unmanaged terrestrial ecosystems. Most current research focuses on BNF of microbes that live in symbiotic association with plant roots. However, free-living N fixing diazatrophs are highly abundant in many soils, and their contribution to ecosystem N cycling is not well understood. While inputs of readily available N such as fertilizer are known to inhibit BNF, very little is known about the relationship between BNF and recalcitrant N availability, or availability of N that is tightly bound in the soil. This is a major knowledge gap, because diazatrophs are very common in environments where the vast majority of N exists in recalcitrant pools. This project will 1) screen diazatroph species to determine the proportion that can access recalcitrant N pools, 2) study the effects of recalcitrant N on diazatroph BNF, and 3) quantify the relationships between BNF and degradation of recalcitrant N. Because N availability is a major limitation for plant growth in most terrestrial ecosystems, this project has significant implications for managing fertilization and agricultural productivity. The project will involve undergraduate and high school students, and the results will be integrated into an inquiry-based learning module for teachers.The role of recalcitrant N in regulating BNF by free-living diazatrophs is entirely unknown. This project proposes and tests a Labile-Atmospheric-Recalcitrant (LAR) N-acquisition strategy, a novel framework for how diazotrophs obtain cellular nitrogen based on cost-benefit principles, with large implications at the ecosystem scale. The project will measure N acquisition of diazatrophs in pure culture under conditions of low labile N but high recalcitrant N availability. These experiments will be followed by pilot incubations in field soils to investigate links between exoenzyme activity and BNF in natural ecosystems. The experiments will contribute to a process-level understanding of BNF by directly characterizing the role of N fixation in the overall N acquisition strategies of diazotrophic microbes. The results will ultimately contribute to microbially-explicit predictive models of BNF in terrestrial ecosystems.

生物固氮（BNF）是将大气中的氮气转化为可供植物吸收的形式。 这一过程由一种称为固氮微生物的微生物进行，占未管理陆地生态系统新氮输入量的 97%。 目前大多数研究都集中在与植物根部共生的微生物的 BNF 上。然而，自由生活的固氮固氮菌在许多土壤中含量很高，但它们对生态系统氮循环的贡献尚不清楚。 虽然众所周知，肥料等容易获得的氮的投入会抑制 BNF，但人们对 BNF 与顽固性氮可用性或紧密结合在土壤中的氮的可用性之间的关系知之甚少。这是一个重大的知识差距，因为固氮菌在绝大多数氮存在于顽固池中的环境中非常常见。 该项目将 1) 筛选固氮菌物种，以确定可以获取顽固氮库的比例，2) 研究固氮氮对固氮菌 BNF 的影响，3) 量化 BNF 与顽固氮降解之间的关系。由于氮的可用性是大多数陆地生态系统中植物生长的主要限制，因此该项目对于管理施肥和农业具有重要意义。 生产力。 该项目将涉及本科生和高中生，其结果将被整合到教师的探究式学习模块中。顽固的 N 在自由生活的固氮菌调节 BNF 中的作用完全未知。 该项目提出并测试了不稳定-大气-顽固性（LAR）氮获取策略，这是一个关于固氮生物如何基于成本效益原则获取细胞氮的新框架，对生态系统规模具有重大影响。该项目将测量在低不稳定氮但高顽固性氮可用性的条件下纯培养物中固氮菌的氮获取情况。 这些实验之后将在田间土壤中进行试点孵化，以研究自然生态系统中外酶活性和 BNF 之间的联系。 这些实验将通过直接表征固氮在固氮微生物整体氮获取策略中的作用，有助于对 BNF 的过程水平理解。 研究结果最终将有助于建立陆地生态系统中 BNF 的微生物显式预测模型。