Hydrogen production by diazotrophs: a novel approach for high frequency measurements of nitrogen fixation

The two main methods to measure rates of nitrogen fixation are the acetylene reduction assay and the 15-N isotope assimilation technique. Here, we present a novel approach to measure nitrogen fixation, by flushing a seawater sample with a gas mixture of argon-oxygen-carbon dioxide and measuring the resulting hydrogen gas produced. We have coupled these measurements to the classical acetylene reduction assay and the 15-N isotope assimilation. The new argon-hydrogen method allows us to measure nitrogen fixation at high frequency and we demonstrate this technique on diazotrophs maintained in culture. Based on the results from culture experiments the instrument is now being configured for deployment on a research vessel in the Pacific Ocean. The new method will provide at-sea measurements of nitrogen fixation in near real time and thereby improve our ability to characterize spatial-temporal patterns in nitrogen fixation in the global oceans.