Biological nitrogen fixation by nitrogenase is often assumed to rely exclusively on molybdenum as an enzymatic cofactor, despite molybdenum scarcity in terrestrial ecosystems and recent demonstrations of vanadium nitrogenase (V-Nase) activity in cryptogamic organisms, collectively responsible for over 40% of terrestrial biological nitrogen input. Here we highlight a global role for vanadium in nitrogen biogeochemistry in extratropical forests’ cryptogams. Measurements in bryophytes and cyanolichens from three continents indicate V-Nase activity in each forest surveyed. We use V-Nase regulation by molybdenum content and nitrogen fixation rates to estimate the global contribution of vanadium to nitrogen fixation by extratropical cryptogams as 30%, with human activities likely responsible for a 30% relative decrease since pre-industrial times. This newly discovered global role of vanadium forces a reevaluation of the nitrogen cycle, where including nitrogenase enzymatic heterogeneity will help better predict the response of the terrestrial carbon sink to global change and understand species biogeography.