Enzymatic diversity of biological nitrogen fixation in a changing world

点击翻译按钮获取中文摘要

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.**