Molybdenum threshold for ecosystem scale alternative vanadium nitrogenase activity in boreal forests

Romain Darnajoux, Nicolas Magain, Marie Renaudin, François Lutzoni, Jean Philippe Bellenger, Xinning Zhang

Research output: Contribution to journalArticlepeer-review

45 Scopus citations


Biological nitrogen fixation (BNF) by microorganisms associated with cryptogamic covers, such as cyanolichens and bryophytes, is a primary source of fixed nitrogen in pristine, high-latitude ecosystems. On land, low molybdenum (Mo) availability has been shown to limit BNF by the most common form of nitrogenase (Nase), which requires Mo in its active site. Vanadium (V) and iron-only Nases have been suggested as viable alternatives to countering Mo limitation of BNF; however, field data supporting this longstanding hypothesis have been lacking. Here, we elucidate the contribution of vanadium nitrogenase (V-Nase) to BNF by cyanolichens across a 600-km latitudinal transect in eastern boreal forests of North America. Widespread V-Nase activity was detected (∼15–50% of total BNF rates), with most of the activity found in the northern part of the transect. We observed a 3-fold increase of V-Nase contribution during the 20-wk growing season. By including the contribution of V-Nase to BNF, estimates of new N input by cyanolichens increase by up to 30%. We find that variability in V-based BNF is strongly related to Mo availability, and we identify a Mo threshold of ∼250 ng·glichen −1 for the onset of V-based BNF. Our results provide compelling ecosystem-scale evidence for the use of the V-Nase as a surrogate enzyme that contributes to BNF when Mo is limiting. Given widespread findings of terrestrial Mo limitation, including the carbon-rich circumboreal belt where global change is most rapid, additional consideration of V-based BNF is required in experimental and modeling studies of terrestrial biogeochemistry.

Original languageEnglish (US)
Pages (from-to)24682-24688
Number of pages7
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number49
StatePublished - Dec 3 2019

All Science Journal Classification (ASJC) codes

  • General


  • Alternative nitrogenases
  • Biological nitrogen fixation
  • Boreal forest
  • Molybdenum limitation
  • Peltigera cyanolichens


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