New research finds fungi that live in healthy plants are sensitive to climate change

Spruces, pines, firs, and other trees dominate the icy expanses of land that stretch across North America, Northern Europe, and Russia, forming a great circle around the world. These boreal forests constitute the largest terrestrial ecosystem and the northernmost forests on the planet.

Nestled in the photosynthetic, or light-eating, tissues of boreal trees – and in the abundant cloud-like lichens and feathery mosses that carpet the ground between them – are fungi. These fungi are endophytes, meaning they live in plants, often in a mutually beneficial arrangement.

“To be a plant is to live in a fungal world,” said Betsy Arnold, a professor in the School of Plant Sciences in the College of Agricultural, Life and Environmental Sciences and the Department of ecology and evolutionary biology from the College of Science and Sciences. member of the Bio5 Institute. “Endophytic fungi are essential to plant health in ways that are not yet fully understood, but what we do know about endophytes in general is that they are very effective in protecting plants from disease and help them be more resilient to environmental stressors, such as heat. They have been part of an important revolution in our thinking about plants.

More than a decade ago, Arnold and his team embarked on a month-long adventure deep into the wilderness of northeastern Canada to understand how these fungal species have adapted to different microenvironments and how they might behave in the face of future climate change.

They discovered great diversity among fungi and that they were adapted very specifically to their local conditions, implying that they will be sensitive to future climate changes. Because the health of fungi is so closely linked to that of their hosts, these findings have implications for the overall health of future boreal forests and our planet.

“Boreal forests play a central role in our planet’s carbon and water cycles,” Arnold said. “And our work highlights that they harbor some of the most evolutionarily diverse fungal endophytes in the world, endophytes that are found nowhere else.”

After more than a decade of analysis, their results were published in the journal Current biology.

“Our collaborative study shed light on the diversity of recently discovered endophytic fungi in the boreal biome and their sensitivity to climate,” said Shuzo Oita, co-senior author of the study, who completed his doctoral studies in the laboratory. of Arnold and is now a research scientist at Sumitomo. Chemical Co., Ltd. “Endophytes are often overlooked because they are found in healthy plant tissues, but their importance in biodiversity and ecosystems has recently been revealed.”

Steal for mushrooms

Collecting the data to reach this conclusion was a gargantuan effort that required Arnold and his colleagues to undertake some of the most intense fieldwork of his life, she said.

For a month in the summer of 2011, the team hired an expert pilot “to get to places where roads don’t lead,” Arnold said. The six-person team traveled through the boreal forests of southern Canada to the edge of the Arctic tundra, landing their seaplane in lakes along the way.

Thirty-six times, they took off and landed in the middle of isolated lakes that dot the landscape. Typically, they spent about six to 24 hours at each sampling site.

By day, they collected healthy spruce leaves and fresh moss and lichens from the ground, storing their scientific treasure in zip-top bags as they went. They also drilled cores of tree rings, hoping to reveal their past, such as their age and exposure to wildfires. They also measured various forest characteristics to understand how plants vary across the landscape.

At night, as the Northern Lights floated overhead, they processed their samples in portable laboratories located inside the pilots’ quarters. They sterilized the surface of fresh tissues to prepare them for DNA extraction and isolated fungal cultures to visualize and document the strains living in their samples.

“We would often work until 2 or 3 a.m. and sleep for a few hours before flying to the next site,” Arnold said. The long days paid off: “In the fungal world, an hour in the field equals a year of characterization and a decade of potential analysis. And in just a few weeks, we’ve come a long way.”

As they traveled from the warmer southern regions to the colder north, they repeated their sampling at intervals of about 100 miles. They also sampled along a single latitude band that was equally large but represented very little climate change, Arnold said.

They carried out strategic sampling across these two dimensions to ensure that any differences in fungal biodiversity were truly driven by environmental differences rather than distance alone. Together, they traveled nearly 1,500 miles in the DeHavilland Otter that was their mobile home, often sharing their travel space with extra fuel tanks.

Older studies have looked at the correlation between biodiversity and latitude, which is often used as a proxy for climate. These studies found that, in general, life becomes more diverse closer to the equator, Arnold said. For example, for many groups of organisms, those in tropical rainforests have greater biodiversity than those in the Arctic tundra.

It turns out it’s not so simple when it comes to mushrooms in the boreal zone.

“We show that boreal fungal communities do not necessarily change with climate in the same predictable way as plant communities. Instead, the effect of climate on these fungi depends strongly on both the fungal species and the host,” said the co-senior author. Jana U’Ren, who completed her doctoral work and conducted the laboratory analyzes for this project as a postdoctoral scientist with Arnold before joining Washington State University. “This means we need to protect plants and their fungal endophytes throughout the boreal biome, not just in one location, otherwise we risk losing vital biodiversity and protective fungi in these important forests.”

Arnold believes that the particular dependence of these fungal endophytes on climate reflects a process of co-evolution with their hosts – or “research and development,” as she put it – as plants find the ideal endophyte partner and s ‘flourish despite the particular stresses that plants face. in these harsh northern landscapes.

“Endophytes are found all over the world, but there are distinctive ones in different environments. We believe that symbioses with endophytes are, in part, how plants overcome environmental challenges on a global scale, it that is, with their internal fungal partners,” Arnold says.

“There isn’t a lot of information about what exactly an individual endophyte does for an individual plant. So our study is fundamental in the sense that we tried to understand who these endophytes are, how they are distributed and how they could change with a changing climate.

She hopes future research can build on their findings.

“What we know is that we lose this biodiversity when these forests change, and we don’t yet know what the key functional elements are,” she said.

Collaborator François Lutzoni, a professor of biology at Duke University and co-architect of this study with Arnold, agrees.

“This is some of the most complex fieldwork I have ever done, but also one of the most exhilarating research experiences I have had,” Lutzoni said.

“Documenting biodiversity in our changing world is essential research. The specimens we collected are deposited in herbaria and therefore have lasting value for understanding how species, their distributions, their genes and the ecosystems they inhabit change over time. for herbaria to serve the scientific community, they must be integrated into the research laboratories of world-class universities.

With this mindset, Arnold now strives to use home-grown endophytes in Arizona to improve crop resilience in this changing world.

“Just as boreal forests harbor an unexpected diversity of endophytes, so do plants here in Arizona,” Arnold said. “Our next steps will be to harness these rich, ancient endophytes as tools to help plants thrive. Ultimately, we hope that by understanding these fungi on a global scale, we can not only trace the past and future of a key part of our planet’s biodiversity., but we can also harness those in our regions to make crops thrive with limited water and rising temperatures. You could say the future is fungal.

Other co-authors are Jolanta Miadlikowska of Duke University, Bernard Ball of University College Dublin and Duke University, Ignazio Carbone of North Carolina State University, Georgiana May of the University of Minnesota, Naupaka B. Zimmerman of the University of San Francisco, Denis Valle of the University of Florida, and Valérie Trouet of the Tree Ring Research Laboratory at the University of Arizona.