Dataset supporting Coming out of the cold: Vanadium is an important player in N-fixation in warm tropical environments

Aim: This study aimed to investigate the presence of vanadium nitrogenase genes in a tropical cyanolichen and assess the impact of micronutrient supply (molybdenum and vanadium) and elevated carbon dioxide concentrations on nitrogen fixation.

Methods and Results: We obtained sequences of vnfN and vnfDG genes from tropical lichen specimens in Brazil and compared them to specimens from deciduous forests in the United States and boreal forests in Canada. Sequences were assembled with sequences from GenBank and aligned with MAFFT using the auto option and then manually corrected in Geneious Prime 2023.2.1. The dataset was then subjected to a maximum likelihood search using IQ-TREE web server with parametric bootstrapping using 1000 replicates under the best-fitted model. The tree inference results were submitted to FigTree 1.4.4 version. Our results revealed that tropical samples form a completely separate group from temperate and boreal samples, and, for the first time, vanadium nitrogenase genes were found in tropical cyanolichens.
We also counted the number of heterocysts on specimens exposed to different treatments to obtain a proxy for nitrogen fixation activity. Paradermal sections of lichen fragments were photographed, and the number of heterocysts and total cells (heterocysts + vegetative cells) was quantified. The results showed a significant influence of carbon dioxide concentrations and vanadium on heterocyst investment.

Conclusions: The findings suggest that vanadium nitrogenase is not an adaptive strategy to cold environments, as this isoform can be found in the tropics. Heterocyst investment, and likely nitrogen fixation, are controlled by carbon dioxide and vanadium. Finally, if we want accurate models of the N cycle, vanadium nitrogenase needs to be considered in the estimates.

The data have been released as part of the manuscript review process at Ecology.