Enzymatic diversity of biological nitrogen fixation in a changing world

北方森林是世界上最大的未受破坏的陆地生态系统之一，并支持加拿大的重要经济部门（即林业，旅游业）。因此，了解北方生态系统的功能具有重要的生态和经济意义。在北方森林中，氮是最常被报道为限制初级生产力的营养物质。虽然北方森林土壤通常富含总氮，但这些氮以植物不易获得的柠檬酸形式结合。因此，森林生长强烈依赖于快速循环的氮和新的氮输入。最后一种来自微生物的生物固氮，特别是蓝细菌，与苔藓和地衣共生互利，或自由生活在土壤中。在未来的几十年里，由于全球气候变化，北方森林将经历前所未有的扰动（例如温度升高，湿度增加）。最近的研究表明，植物的氮供应可能在北方森林对全球气候变化的反应中发挥关键作用。 因此，了解控制北方森林生物固氮的过程对于以可持续的方式管理北方自然资源至关重要。生物固氮依赖于固氮酶的活性，该酶将大气中的二氮还原为生物可利用的铵。虽然固氮酶的三种异构体已被确定，生物固氮被认为主要取决于钼异构体。最近的研究，由我的实验室和同事进行，已经强调，其他两个异构体，使用钒和铁，发挥更重要的作用，生物固氮比以前接受。这些发现显着改变了传统的观点，钼是主要的金属维持生物固氮，并邀请我们整合固氮酶的多样性在我们的概念模型连接金属动力学和生物固氮。 这项研究计划将解决有关生物固氮在北方生态系统的关键问题。它将显着改善我们的概念模型连接微量营养素动态和生物固氮提供新的见解替代固氮酶的贡献，生物固氮在北方森林以及其潜在的作用，北方森林对全球气候变化的反应。确定固氮酶多样性在环境中的真实的重要性具有潜在的变革性，因为它深刻影响了我们理解和估计该领域生物固氮的方式。这项研究将最终帮助北方森林的最终用户（例如林业）和决策者改进加拿大自然资源管理政策和做法。

The boreal forest is one of the largest untouched terrestrial ecosystem in the world and supports essential economic sectors (i.e forestry, tourism) in Canada. Understanding boreal ecosystems function is thus of prime ecological and economical importance. In boreal forests, nitrogen is the nutrient that is most often reported as limiting primary productivity. While boreal forest soils are often rich in total nitrogen, this nitrogen is bound in recalcitrant forms that are not readily available to plants. Therefore, forest growth strongly relies on rapidly cycling nitrogen and new nitrogen inputs. The last arises from biological nitrogen fixation by microorganisms, especially cyanobacteria, involved in symbiotic and mutualistic associations with mosses and lichens or living freely in soil. In the next decades, the boreal forest will undergo unprecedented perturbations (e.g. increased temperature, humidity) due to global climate change. Recent studies reported that nitrogen availability to plants will likely play a critical role in the response of the boreal forest to global climate change. Understanding processes controlling biological nitrogen fixation in boreal forest is thus essential to the management of boreal natural resources in a sustainable manner. Biological nitrogen fixation relies on the activity of the enzyme nitrogenase which reduces atmospheric dinitrogen into bioavailable ammonium. While three isoforms of the enzyme nitrogenase have been identified, biological nitrogen fixation is assumed to depend primarily on the molybdenum isoform. Recent research, conducted by my laboratory and colleagues, have highlighted that the two other isoforms, using vanadium and iron, play a more significant role on biological nitrogen fixation than previously accepted. These findings significantly alter the traditional views that molybdenum is the predominant metal sustaining biological nitrogen fixation and invite us to integrate nitrogenase diversity in our conceptual models linking metal dynamics and biological nitrogen fixation. This research program will address critical questions regarding biological nitrogen fixation in boreal ecosystems. It will significantly improve our conceptual models linking micronutrient dynamics and biological nitrogen fixation by providing new insights into the contribution of alternative nitrogenases to biological nitrogen fixation in boreal forests as well as their potential role in the response of boreal forests to global climate change. The determination of the real importance of nitrogenase diversity in the environment is potentially transformative as it deeply affects the way we comprehend and estimate biological nitrogen fixation in the field. This research will ultimately help boreal forest end-users (e.g. forestry) and decision makers to improve Canadian natural resources management policies and practices.