Climate change disrupting fungal balance in woodland soils

New research from Stanford suggests climate change will disrupt many age-old partnerships between aspen trees and fungi that are essential to healthy forests.

Hidden in the roots, soil, and fluttering leaves of an aspen grove are complex networks of fungi. Some fungi in these networks can help aspens and closely related trees in the genus Populus absorb water and nutrients from soil, while others may cause disease in the plants’ leaves.

Recent research from Stanford University suggests climate change will disrupt the balance between helpful and harmful fungi in Populus groves, as rising temperatures and shifting precipitation patterns lead to fewer kinds of beneficial soil and root fungi in drier regions and encourage growth of potentially pathogenic leaf fungi in wetter areas.

Senior study author, Kabir Peay, from the Stanford Doerr School of Sustainability, said, “There are a lot of questions to answer if we want to understand how these microbial communities are going to influence the future of really important ecosystems.”

The new study catalogues the diversity of fungi associated with five Populus species at 94 groves in 21 US states, building on more than a decade of work by the Peay Lab at Stanford to map fungal diversity and understand its relationship to the future of forests.

The study, published in November last year in Nature Microbiology, also predicts how different groups of fungi associated with Populus trees will respond to climate change – expanding on past research from the group focused on symbiotic microbes in pine forests.

In extremely dry places like the deserts of the US southwest, the authors found the trees tended to have a unique species of mycorrhizal fungus, which connects to a plant’s roots and helps it obtain water and nutrients. As they simulated more extreme temperatures and droughts predicted under climate change in these areas, the abundance of mycorrhizal fungi increased, suggesting that the trees may get extra help from fungi to quench their thirst when water is scarce. But the array of mycorrhizal fungus species in these parched environments was far less diverse than in more moderate climates, and is predicted to drop even further if temperatures rise.

The results suggest that as global warming brings increasingly hot and dry weather to the southwest, vulnerable Populus trees may be left with fewer fungal symbionts to choose from. Fungi tend to prefer more humid environments, so it’s likely that many species won’t be able to handle the lack of moisture.

Co-lead study author, Michael Van Nuland, a lead data scientist with the Society for the Protection of Underground Networks (SPUN), said, “Diversity is really important for stability and overall productivity of these systems, so it’s quite concerning that we might see fungal diversity decline.”

Future conservation
Because of their large ranges, ability to thrive across a variety of ecosystems, and quick regrowth after wildfires, Populus trees support thousands of other species, sequester significant amounts of carbon in the soil, and provide other vital ecosystem services. Understanding how Populus trees interact with fungal communities and how those relationships are likely to change in the future could inform forest conservation and restoration across North America.

If researchers can identify which microbes are best adapted to helping trees survive in warmer temperatures, for example, it might be possible to add those fungi to soil or leaves to help trees cope with the climate. It could also help with cultivation efforts: Populus species are being considered as a source for biofuels because of their rapid growth.

Climate-driven changes in fungal communities could affect the health of forest ecosystems around the world, as most tree species rely on fungal partnerships to thrive. Mycorrhizal fungi in the roots and surrounding soil not only help trees cope with drought, they also often act as trade partners, accepting carbon in exchange for nutrients that trees need, such as phosphorus and nitrogen. Plenty of others likely function in ways that scientists haven’t identified yet.

Changing conditions, changing communities
To get a broad sample of the fungal communities that coexist with Populus trees, the researchers collected leaves, roots, and soil from Populus groves in areas ranging from the deserts of Arizona and the humid forests of Louisiana to as far north as the Canadian border. Within each sample, they identified which fungi were present and how common they were, finding more than 9,500 types of fungus in all.

Co-lead study author, Caroline Daws, who is a lecturer at Stanford, said, “Some of these Populus species have huge geographic ranges. Looking at the same species in a lot of different environmental conditions – different soil types, temperatures, seasonal precipitation – gave us a sense of the full diversity of fungi that can associate with these trees and how individual populations of trees might survive in really different environments.”

“We hope that this work helps shed light on the immense diversity of fungal life that’s in our soils and in our plant communities,” said Kabir Peay. “We can’t easily see them with our eyes, but they have a big impact on the world around us.”

Read the paper, Above- and belowground fungal biodiversity of Populus trees on a continental scale

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