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

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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.