As warming temperatures shift the timing of snowmelt, a critical water source for high mountain ecosystems, some relationships between organisms, like plants and pollinators, can fall out of sync.
But according to a CU Boulder study, published in Arctic, Antarctic, and Alpine Research, ecologists found that the partnership between underground fungi and plants appeared to be resilient to the changing snowmelt timing.
“It turns out shifting conditions caused by climate change may not always affect ecosystems in simple, direct ways,” said Annie Meeder, a doctoral student in the Department of Ecology and Evolutionary Biology and the Institute of Arctic and Alpine Research. “In this case, rather than the relationship breaking down in the face of changing conditions, these partnerships seem to be able to respond and adapt to changes in plant growth and development.”
Plant roots under the microscope (in blue). Dark lines are arbuscular mycorrhizal fungi. (Credit: Annie Meeder and Cliff Bueno de Mesquita/CU Boulder)
Many fungi in soil form symbiotic relationships with plants. They rely on plants for sugar while helping plants extract nutrients from the soil. It is estimated that more than 80% of land plants have fungal partners. In harsh environments like the alpine, plants rely even more heavily on fungi to thrive.
Warming temperatures and snowmelt are vital environmental cues for alpine organisms to emerge from their winter inactive state.
Across the American West, snowpacks have been melting earlier. This past spring, an unprecedented heat wave caused Colorado’s snowpack to melt more than a month early.
Previous studies have shown that rising temperatures and changes in snowmelt patterns are leading to mismatches in when plants flower and when pollinators become active. Meeder and her team wondered if the changes were also affecting the plant-fungi partnership.
Between 2018 and 2023, the researchers spread a layer of dark sand over four plots of land at the Niwot Ridge Long-Term Ecological Research site just west of Boulder, Colorado, at an elevation of more than 11,000 feet. At the research site, annual maximum temperatures have increased by 0.5°C (0.9°F) per decade since the 1950s, which has advanced snowmelt.
The black sand treatment shifted snowmelt on the plots by an average of 10 days compared with the untreated plots next to them.
The team then collected root samples from 104 plants growing in the plots and tested them for several types of symbiotic fungi, including arbuscular mycorrhizal fungi (AMF), which can help plants acquire nutrients and better tolerate drought, as well as dark septate endophytes and fine root endophytes.
They found that early snowmelt didn’t affect how many fungi partners plants were able to recruit. Instead, plants that produce seed earlier in the season tended to have fewer fungi attached to their roots, while plants that did so later tended to have more fungi, regardless of snowmelt timing.
Seed setting is a highly resource-intensive process for plants. Meeder explained that when snow first starts to melt in the spring, microbes in the soil unleash a burst of nutrients that helps jump-start alpine plants. For plants that can take advantage of the nutrient surge and produce seeds early, fungal support may be less important than it is for plants that produce seeds later in the growing season, when nutrients dry out and plants may rely more on their fungal partners.
While snowmelt timing can affect when plants produce seeds, the finding suggests that fungi are mainly responding to signals from plants instead of the environmental cue itself, allowing them to stay in sync.
But there may be limits to that resilience, Meeder said. If the alpine environment becomes even hotter and drier in the future, organisms could eventually be pushed beyond their ability to maintain the partnership.
“Fungi rule the world,” Meeder said. “They grow our crops, and they’re in our bodies. It’s very encouraging to see this relationship staying resilient to early snowmelt at this point, but it’s something we should continue to pay attention to. We need to understand how much change these relationships can absorb before that resilience begins to break down.”