This is the first paper of the collaborative grant led by Fay-Wei Li to do a worldwide assessment of the symbiosis between hornworts and nitrogen-fixing cyanobacteria. What's so new about a vanadium nitrogenase? The nitrogenase with a vanadium co-factor had only been  reported from free-living bacteria and cyanobacteria associated to boreal lichens. This "alternative" nitrogenase  is thought to be more active at low temperatures (below 14C) and it plays a crucial role in the nitrogen cycl...