29-year study reveals changes in climate reshape plant communities, soil ecosystems
In the longest-running field warming experiment of its kind, researchers have documented dramatic shifts in high-elevation mountain meadows, revealing that changes in climate alter not only the plants we can see above ground, but the invisible world of fungi and microbes in the soil below.
The results, published in an article in The Proceedings of the National Academy of Sciences and co-led by University of Michigan researcher Aimée Classen, show that sustained warming is causing meadows to undergo "shrubification," a transition from diverse grasslands and flowering plants to shrub-dominated landscapes, and that the ecosystem belowground is responding in kind.
Specifically, while the meadows changed from grasslands to shrublands, the types of fungi associated with plant roots in the soil beneath the meadows changed as well. In the original grassland ecosystem, plants relied heavily on mycorrhizal fungi-beneficial partners that help plants absorb water and nutrients from the soil in exchange for carbon. Under warming conditions, however, these mutualistic relationships declined dramatically, and soil saprotrophic fungi, which are involved in the decomposition of organic matter, increased.
"It's a shift from a meadow that eagerly chases resources to a shrub land holding onto nutrients tightly," said Classen, study co-principal investigator, professor of ecology and evolutionary biology and director of the U-M Biological Station. "In addition, warming is uncoupling the intricate connections between plants and soil fungi. When these connections fray, the ecosystem begins to change, not just in who lives there, but also how energy and nutrients move through the system and what it can provide to wildlife and people."
For nearly three decades, heaters warmed experimental plots of ground year-round at the Rocky Mountain Biological Laboratory in Colorado in order to replicate conditions that may exist under climate change. For most of that time, researchers documented how the meadow plant life transitioned from productive grasslands dominated by species like fescue and sunflowers to conservative shrub communities dominated by sagebrush.
"What is really exciting about these findings is that they demonstrate that not only do plant communities shift, which has been documented before, but the soils that are associated with these communities can also change," said Lara Souza, co-principal investigator and researcher from the University of Oklahoma.
In 2019, the research team, which also includes Stephanie Kivlin of the University of Tennessee and Jennifer Rudgers of the University of New Mexico, wanted to understand if this change meant that soil beneath the meadow was being impacted as well.
The team dug meters down into the soil in order to collect samples, which told the researchers what was happening to the fungal communities below the meadow. They discovered that the soil ecosystem is changing alongside the plants, fundamentally altering how these systems function.
"We show that mycorrhizal fungi and decomposers are not reacting to environmental change the same way as plants, which can result in an unexpected loss of microorganisms under future climates," Kivlin said. "We expected that after 29 years of warming, that mycorrhizal fungi could adjust or acclimate to the higher temperatures, but the fact is that they can't, and that has consequences for ecosystem carbon and nutrient cycles."
These changes alter key services that ecosystems provide, such as foraging land for wildlife. The original herbaceous meadow provided rapid nutrient cycling, meaning that plants quickly absorbed nutrients from the soil, incorporated them into their tissue, and returned them to the soil when they died. By contrast, the new shrub-dominated environment operates much more slowly and conservatively. Under these new conditions, the grassland areas become drier and more arid.
"It's not only the visible shift from wildflowers to shrubs, but also the invisible loss of synergy between plants and their microbial partners," Classen said. "That's where ecosystem resilience, productivity and the capacity to handle change really begins to unravel."
Study: Experimental warming decouples plant-fungal symbiont interactions and leads to a more conservative ecosystem (DOI: 10.1073/pnas.2510936123) (study available upon request)
Written by Kathryn Gebauer, University of Oklahoma
