EAGER: Method development for the assessment of spatiotemporal variability of non-symbiotic N2 fixation

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Non technical abstractDinitrogen (N2) fixation, the biological reduction of atmospheric N2 to ammonium, is the main route of new nitrogen (N) to ecosystems. It influences plant growth and carbon exchange at local, regional and global scales. Our understanding of natural N2 fixation however remains limited, especially in terrestrial environments where it is systematically underestimated. Because fully understanding, or "closing" the N budget of terrestrial ecosystems depends on a better measurement of non-symbiotic N2 fixation, there is a pressing need for new analytical techniques allowing for an affordable, highly sensitive, continuous and non disturbing assessment of non-symbiotic N2 fixation. This is the objective of the proposed work. Briefly, the PIs propose to develop a new method to monitor the reduction of acetylene to ethylene (the most commonly used surrogate for N2 fixation measurements) by wavelength-scanned cavity ring down spectroscopy (WS-CRDS). The portability and high sensitivity of the device will allow for high frequency surveying of large surfaces and provide an innovative tool to study the poorly-resolved spatial variability and short-term responses to environmental gradients of terrestrial N2 fixation. This work also answers a pressing demand for improved tools to assess on-site variability of N2 fixation.