Lichens are some of the most inconspicuously amazing organisms out there. They’re essentially composite, symbiotic organisms made from a fungus and algae or cyanobacterium living among the filaments of fungi. Lichens can grow almost everywhere, from the Arctic tundra to the bark of a tree in your backyard. However, this apparent resilience is being challenged by the climate crisis, with a study showing they have a very tough time adapting to rising temperatures.

Matthew Nelsen from the Field Museum in Chicago and his colleagues investigated how the climate preferences of lichen change over time and how this relates to the climate crisis. As it turns out, they shift temperature preferences by less than 1ºC every million years. This is lower than the global warming of up to 3ºC predicted.

“Our initial motivation was to better understand how this important group of algae had diversified to collectively occupy an extremely wide range of climates across the globe,” Nelsen told ZME Science. “It was an exciting opportunity for us to use the past to make predictions about how these algae may be affected by modern climate change.”

Exploring lichens

Nelsen and colleagues focused on a single genus of algae, Trebouxia, which is found in about 7000 species of lichen. When algae take residence inside a lichen, they live with the fungus as one — each providing something that benefits the whole. The algae provide food through photosynthesis, while the fungus provides the physical structure.

The team gathered plenty of data on where Trebouxia occurs across the world, observing the climate conditions of each location. They also worked with a database of Trebouxia genes to create a family tree for the algae. All this information was then used to estimate how fast Trebouxia has adapted to a changing climate in the past.

They found that the change in the climate preferences of the algae happens very slowly over the course of millions of years. This means that Trebouxia is likely to be impacted by the fast climate change that the planet is currently going through. If they can’t adapt fast enough, they might have to modify at least part of their current range.

The researchers believe that lichens that rely on Trebouxia will likely disappear from many of the places they are found today. Some might migrate to other places with more tolerable climate conditions, but environmental degradation caused by humans also means that there are limits to the area where the lichens could spread into.

Fewer lichens would have deep consequences on ecosystems, as they are the dominant vegetation on 7% of the Earth’s surface, Nelsen said. They are important for ecosystem hydrology as well as for carbon and nitrogen cycling. But there’s no need to despair. We can still reduce our emissions and do further research on lichens, he said.

“One question that has repeatedly come up is whether the fungal partners exhibit a similarly low historic rate of change.  This would be especially interesting to pursue,” Nelsen said. “It would also be wonderful to have experimental data demonstrating the thermal limits and optima of these algae to gain a better understanding of them.”

The study was published in the journal Frontiers.