Niche constraints drive differences between mycorrhizal fungal guilds in future range shifts

Beneath our feet, in the dark soil of forests, fields, and gardens, lives a vast and invisible network of fungi. These are not the mushrooms we see popping up after a rain, but thread-like organisms that form intimate partnerships with plant roots. Scientists call them mycorrhizal fungi. They act as an extension of the plant's root system, reaching out to gather water and nutrients that the plant cannot access on its own. In return, the plant feeds the fungi sugars produced by sunlight. This exchange is so fundamental that it occurs in ninety percent of all plant species on Earth, making these fungi essential engineers of the global ecosystem. They help regulate how much carbon the planet stores and how nutrients cycle through the soil. Yet, despite their importance, we know very little about where these fungi live, how much territory they cover, or how they will respond as the world warms.

A new study has begun to fill this massive gap in our knowledge by mapping the homes of hundreds of these fungal partners. Researchers gathered a staggering amount of data—over 115,000 samples of fungal DNA collected from soils and roots all around the globe. Using this data, they created a detailed atlas of where 651 common types of these fungi currently exist. They then used computer models to predict how these living ranges will change as the climate shifts over the coming century. The work reveals that not all fungi are built the same way. Some are generalists, comfortable in a wide variety of conditions, while others are specialists, thriving only in very specific environments. This difference in flexibility will determine which fungi survive the changes ahead and which will struggle to find a place to live.

The researchers focused on two main groups of these fungi. The first group, known as arbuscular mycorrhizal fungi, is an ancient lineage that partners with a vast array of plants, from grasses to tropical trees. The second group, called ectomycorrhizal fungi, is more diverse and tends to associate with trees like pines, oaks, and birches. By analyzing the environmental conditions where each type was found, the team discovered that these two groups occupy very different worlds. The arbuscular fungi are the wanderers of the soil; they are found across a much wider range of temperatures, rainfall patterns, and soil types. They can live in hot, wet tropical forests as well as in drier, cooler regions. In contrast, the ectomycorrhizal fungi are more picky. They tend to cluster in colder, drier biomes, such as the boreal forests of the north and cold temperate zones. Their homes are more restricted, and they are less able to tolerate a broad spectrum of environmental conditions.

This difference in flexibility extends to what drives their presence in a specific location. For the ectomycorrhizal fungi, the climate is the dominant force. Temperature and rainfall patterns are the primary keys that unlock where they can grow. Their existence is tightly bound to the weather. The arbuscular fungi, however, are influenced by a more complex mix of factors. While climate matters to them, their distribution is also strongly shaped by the local soil, the type of plants growing above ground, and even human activity like burning or land use. They are less dependent on the broad climate and more responsive to the immediate details of their local neighborhood. This suggests that the arbuscular fungi have a broader "niche," a term scientists use to describe the full range of conditions a species can tolerate. The arbuscular fungi can handle a much wider variety of situations than their ectomycorrhizal counterparts.

The study then looked ahead, using future climate scenarios to see how these ranges might shift. The models predict a sobering trend: the suitable living space for these fungi will shrink for almost all of them. Under a high-emissions scenario, where greenhouse gas levels continue to rise unchecked, the total area where these fungi can survive is projected to decrease by nearly fourteen percent. That amounts to a loss of roughly 2.2 million square kilometers of habitat. This loss is not shared equally between the two groups. The ectomycorrhizal fungi, with their narrower and more climate-dependent niches, are expected to suffer the most. Their suitable ranges are predicted to contract by about twenty-six percent on average. The arbuscular fungi, with their broader tolerance, will also lose ground, but their ranges are expected to shrink by a smaller margin, around seven percent.

The researchers found that the fungi with the smallest, most specific niches are the ones most vulnerable to these changes. For the ectomycorrhizal group, there is a clear link: the more limited a fungus's environmental preferences, the more its range is likely to disappear as the climate changes. This relationship was not as clear for the arbuscular fungi, whose broader adaptability seems to buffer them against the worst effects, at least in these simulations. The study also highlighted that even within the same group of fungi, there is huge variation. Some species of the same genus might lose almost all their habitat, while others in the same family might actually gain ground or remain stable. This means that the future of fungal biodiversity will not be a uniform decline but a complex reshuffling where some specialists vanish and generalists persist.

These findings offer a critical baseline for understanding the future of our planet's underground life. Because these fungi are so deeply tied to the health of forests and the cycling of carbon, their decline could have ripple effects that reach far beyond the soil. If the fungi that help trees absorb nutrients disappear, the trees themselves may struggle to survive, potentially altering how forests store carbon and respond to drought. The study does not claim to have solved the mystery of fungal distribution, nor does it account for every factor, such as how fast fungi can move to new areas or how they might adapt evolutionarily. However, by mapping the current homes of these organisms and modeling their future, the researchers have provided a clear warning. The world is changing faster than some of its most important underground partners can keep up with, and the consequences of losing these specialized fungi could reshape the ecosystems we rely on.