@article{126, author = {X. Zhang and D.L. McRose and and J.-P. Bellenger and F.M.M. Morel and }, title = {Alternative nitrogenase activity in the environment and nitrogen cycle implications}, abstract = {Biological nitrogen fixation, the main natural input of fixed nitrogen into the biosphere, is catalyzed by Mo-, V-, or Fe-only nitrogenase metalloenzymes. Although {\textquotedblleft}alternative{\textquotedblright} V- and Fe-only nitrogenase genes are found in many environments, the contribution of these isoenzymes to N2 fixation is unknown. Here we present a new method (ISARA, isotopic acetylene reduction assay) that distinguishes canonical Mo and alternative nitrogenase activities based on in vivo 13C fractionation of acetylene reduction to ethylene (13εMo~=~13.1{\textendash}14.7~{\textperthousand}, 13εV~=~7.5{\textendash}8.8~{\textperthousand}, 13εFe~=~5.8{\textendash}6.5~{\textperthousand}). ISARA analyses indicate significant contributions of alternative nitrogen fixation in boreal cyanolichens and salt marshes ( 10{\textendash}40~\% acetylene reduction, 20{\textendash}55~\% N2 fixed). These results affect the quantitative interpretation of natural abundance 15N data or traditional acetylene reduction assays. They also invite a reexamination of the conditions under which the different nitrogenase isozymes are active and suggest significant interactions between the cycles of nitrogen and trace metals. {\textcopyright} 2016, Springer International Publishing Switzerland.}, year = {2016}, journal = {Biogeochemistry}, volume = {127}, number = {2-3}, pages = {189-198}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84959510549\&doi=10.1007\%2fs10533-016-0188-6\&partnerID=40\&md5=2d79969649861e03132dd00e70c8e25b}, doi = {10.1007/s10533-016-0188-6}, }