Warming Winters Are Threatening the Fungi That Keep Mountain Grasslands Alive
- Gauri Khanna
- 2 days ago
- 3 min read
Too long to read? Go for the highlights below.
Arbuscular mycorrhizal fungi, found in over 75% of plant species, are being disrupted by warmer winters and reduced snowpack, leaving plants less able to absorb nutrients.
A 30-year warming experiment in Colorado's Rocky Mountain grasslands showed a marked decline in beneficial fungi, with the ecosystem shifting from diverse grassland towards scrubland.
When snowmelt arrives too early, fungi and plant roots fall out of sync: nutrients leach away before plants can use them, with potentially cascading effects on the wider food web.
A snowy winter landscape may look dormant, but beneath the surface a quiet economy is running at full tilt. Soil microorganisms, fungi chief among them, are breaking down dead plant matter and cycling nutrients that will feed the first green shoots of spring. Disrupt that subterranean activity, and the consequences ripple upwards through entire ecosystems. New research from the United States suggests that warmer winters are doing precisely that, with troubling implications for grasslands that support both wildlife and livestock across mountainous regions.
The Underground Partnership Climate Change Is Quietly Undermining
Central to this story are arbuscular mycorrhizal fungi: microscopic, thread-like organisms that colonise the roots of more than three-quarters of all plant species on Earth. Rather than existing as passive passengers, these fungi form a genuine exchange: they channel up to half of a plant's required nutrients and water in return for carbon produced by the plant through photosynthesis. Think of them as a subterranean trading network, invisible but indispensable.
In winter, a thick snowpack acts as an insulating blanket, keeping soil temperatures stable enough for these fungi and other microbes to carry on their work even as air temperatures plunge below freezing. The problem arises when that blanket disappears, whether through rain-on-snow events that erode the snowpack or simply through winters that never accumulate enough snow in the first place. When that happens, soil can freeze solid for longer periods, suppressing microbial activity and depleting the nutrient reserves that plants depend upon come spring.
Mycorrhizal fungi's role in soil health and carbon cycling is already well documented, but this research adds an important seasonal dimension to that picture.
Three Decades of Evidence from Colorado's Subalpine Meadows
Researchers at a long-running field site in Colorado's Rocky Mountain grasslands have been artificially warming plots of land by 2°C for 30 years: approximating the temperature increases the region could experience by the end of this century. The results above ground were stark: the plots shifted from species-rich grassland dominated by grasses and wildflowers towards scrubby, more desert-like vegetation. Below ground, the researchers recorded a notable decline in beneficial mycorrhizal fungi, weakening the ability of remaining plants to acquire nutrients or tolerate stresses such as drought and frost.
A separate early-snowmelt experiment, initiated in April 2023, offered a complementary insight into timing. When snowmelt was advanced by roughly two weeks, mycorrhizal fungal growth accelerated by about a week, but plant root growth showed no corresponding shift.
This matters because plants largely respond to light cues, whilst underground fungi respond to temperature and nutrient signals. The two partners, finely tuned to act in concert, are being pulled apart by a changing climate. When fungi are active before plants, any nutrients the fungi gather cannot be transferred to their plant partners, and those nutrients may instead leach away into waterways, much as fertiliser runoff from farmland fuels algal blooms in rivers and lakes.
This kind of nutrient loss has been observed across a range of ecosystems, from mountain grasslands in Colorado to temperate forests in New England: suggesting the phenomenon is neither localised nor anomalous.
What This Means for Ecosystems and Agriculture
The downstream consequences extend well beyond the plant world. Grasses and wildflowers support cattle grazing and provide habitat for wildlife; their replacement by scrubland diminishes the productivity and biodiversity of these landscapes in ways that could prove difficult to reverse. Fungi's broader role in rebuilding degraded agricultural soils underlines just how much modern land management depends on maintaining healthy fungal communities.
There is some measured optimism. Ecosystems are resilient, and both plants and fungi may adapt: shifting their ranges or acclimating to lower nutrient availability over time. Yet the pace of climate change may outstrip the capacity for that adjustment. How well these underground partnerships respond will, in large part, determine the fate of mountain grasslands as winters continue to warm. The lesson, perhaps, is that protecting these ecosystems begins not with what we can see above ground, but with the invisible networks working beneath our feet.
