Abstract
Nitrogen (N)‐fixation is a crucial source of reactive N in terrestrial environments. The nitrogenase enzyme (Nase), responsible for this conversion, has three isoforms: molybdenum (Mo)‐, vanadium (V)‐, and iron (Fe)‐Nases. The Mo‐Nase is found in all N‐fixers, but the distribution pattern and drivers of V‐ and Fe‐Nases remain poorly understood. Carbon and micronutrients (Mo and V) might be key contributors to N‐fixation by affecting the metabolic demand for N and participating in Nase synthesis, respectively. Here, we investigated the presence of V‐Nase genes in a tropical cyanolichen and explored the impact of micronutrient supply and elevated carbon dioxide (CO 2 ) concentrations on N‐fixation. The experiment revealed a significant influence of V and CO 2 concentrations on heterocyst investment. V‐Nase genes were also detected in tropical lichen specimens, suggesting that tropical species might have both Mo‐ and V‐Nases. Our study suggests that V‐Nase is prevalent beyond cold environments, by reporting its presence in the warm tropics and demonstrating a significant response of N‐fixing cells to V addition. We emphasize the importance of further research on N‐fixation in the tropics, particularly on the role of different Nase isoforms.