Microbes colonize new lava at an Iceland volcano ^{CEFR B2}

Researchers examined primary microbial succession on fresh lava flows at the Fagradalsfjall volcano in southwestern Iceland after three eruptions between 2021 and 2023. Led by ecologists and planetary scientists at the University of Arizona, the team sampled newly cooled lava within hours of solidification and also gathered rainwater, aerosols, soil and surrounding rock. The study, with Nathan Hadland as first author, appears in Nature Communications Biology and includes coauthors from the University of Iceland.

The investigators extracted DNA from these samples and combined statistical analysis with machine learning to identify organisms and infer their likely sources. Hadland noted that lava starting at more than 2,000 degrees Fahrenheit is initially sterile. Fresh flows contain very little water and almost no organic nutrients, making them among the lowest-biomass environments on Earth, comparable to Antarctica or the Atacama Desert, as Solange Duhamel explained.

Results show that biodiversity increased during the first year after eruption but then "tanked" following the first winter, when seasonal conditions selected for a smaller set of surviving microbes. After that shift diversity changed less and began to stabilize. The analysis indicates a clear pattern: early colonizers largely arrived from nearby soil and from aerosols deposited on the lava, whereas after the winter most microbes appeared with rainwater. The team points out that rainwater is not sterile and can carry microbes that also serve as cloud condensation nuclei. The authors say sampling three eruptions provided a rare triplicate and that the findings can inform questions about how volcanism might create temporary habitable conditions on worlds such as Mars and what biosignatures to seek. Funding came from sources including the National Science Foundation and the Heising–Simons Foundation.