Enzymatic diversity of biological nitrogen fixation: above, below and beyond cyanolichens.

生物固氮(BNF)是氮循环的关键反应，也是向未管理的生态系统提供新氮的重要来源。该反应由钼固氮酶和两种互补固氮酶(COMP-Nase)催化，即钒固氮酶和铁固氮酶。更好地评估哪些固氮酶对生物固氮酶的固定具有重要意义，这对于估计氮输入和理解痕量金属动力学与生物固氮之间的联系具有重要意义。目标-我的研究计划的长期目标(10-15年)是破译痕量金属动力学和氮循环之间的联系。我的短期目标(未来5年)是在地球尺度上破译生物固氮的发生和贡献。为了实现这一目标，在接下来的5年里，我的研究计划旨在：(1)评估复合酶对北方羽毛苔藓生物固氮的贡献，(2)评估复合酶对与高等植物基质(叶圈和根际)相关的生物固氮的存在和贡献，(3)研究温度的作用及其与钼有效性的交互作用，(4)调查地球尺度上复合酶的贡献，(5)估计人为来源的钼如何改变氮的利用(钼氮与钼氮的作用)。研究方法--这项研究计划包括实地和实验室实验。它将依赖于一系列分析工具来进行生物基质中的元素分析，分子生物学来表征固氮酶基因的存在和表达以及氮固定群落，以及分析化学来评价生物固氮酶。影响-这项研究计划将有助于弥合关于BNF的组成部分的作用和控制其使用的环境驱动因素的多个知识空白。破译生物固氮在生态系统和地球尺度上的存在和贡献具有潜在的变革性，因为它深刻地影响了我们在该领域理解和估计生物固氮的方式。例如，大多数N输入估计来自高度依赖固氮酶异构体的未经校准的乙炔还原试验。如果比较比以前认为的更重要，将需要对N个投入估计进行深刻的重新评估。它还质疑我们对金属对主要营养循环(即N)的控制的理解。与钼相比，钒可能是生物圈中一种关键的生物金属，其生物地球化学循环和与微生物的相互作用仍未得到很好的描述。由于N个投入估计用于多种目的，这项研究最终将帮助最终用户(例如林业)和决策者改进加拿大自然资源管理政策和做法。

Context - Biological nitrogen fixation (BNF) is a key reaction of the N cycle and an important source of new N to unmanaged ecosystems. This reaction is catalyzed by three isoforms, the molybdenum-based nitrogenase, and two complementary nitrogenases (comp-Nases); the vanadium based nitrogenase and the iron-only nitrogenase. Better evaluating which nitrogenases contribute to biological nitrogenase fixation has important implications for the estimation of N inputs and our understanding of the link between trace metal dynamics and BNF. Objectives - The long-term objective (10-15 years) of my research program is to decipher the link between trace metal dynamics and nitrogen cycling. My short term objective (next 5 years) is the decipher the occurrence and contribution of comp-Nases to BNF at the earth scale. To achieve this goal, over the next 5 years my research program aims at (1) evaluating the contribution of comp-Nases to boreal feather moss BNF, (2) assessing the presence and contribution of comp-Nases to BNF associated with higher plants matrices (phyllosphere and rhizosphere), (3) investigating the role of temperature, and its interaction with Mo availability, on the use of comp-Nases, (4) investigating the contribution of comp-Nases at the earth scale, (5) estimating how Mo of anthropogenic origin altered Nases use (Mo-Nase versus comp-Nases). Methodology - This research program includes both field and laboratory experiments. It will rely on a series of analytical tools for elemental analysis in biological matrices, molecular biology for the characterization of nitrogenase genes presence and expression and N2 fixing community, and analytical chemistry for the evaluation of BNF. Impact - This research program will contribute to close multiple knowledge gaps regarding the role of comp-Nases to BNF and the environmental drivers controlling their use. Deciphering the occurrence and contribution of comp-Nases to BNF at the ecosystem and earth scale is potentially transformative as it deeply affects the way we comprehend and estimate BNF in the field. For instance, most N input estimates derives from uncalibrated acetylene reduction assay which is highly nitrogenase isoforms dependent. If comp-Nases are more important than previously believed a profound reassessment of N input estimates will be required. It also questions our understanding of metals control over major nutrient cycling (i.e., N). Vanadium is likely a critical biometal for the biosphere which biogeochemical cycling and interactions with microorganisms remains poorly characterized, in comparison to its molybdenum counterpart. Because N input estimates are used for multiple purposes, this research will ultimately help end-users (e.g., forestry) and decision makers to improve Canadian natural resources management policies and practices.