Agroecology and plant-microbiome interactions

Source:

University of Zurich

Summary:

When trees and soil fungi form close associations with each other, both partners benefit. Many tree species have further enhanced this cooperation by forming a concurrent symbiosis with two different groups of mycorrhizal fungi. Those trees cope better with water and nutrient scarcity, which is an important trait for forestry in the face of climate warming.

FULL STORY

When trees and soil fungi form close associations with each other, both partners benefit. Many tree species have further enhanced this cooperation by forming a concurrent symbiosis with two different groups of mycorrhizal fungi. Those trees cope better with water and nutrient scarcity, which is an important trait for forestry in the face of climate warming.

Despite having enormous root systems, trees often are unable to take up enough water and nutrients from soil to grow in a healthy manner.

That's why most terrestrial plants have formed symbiotic associations with fungi over the course of evolution.

These mycorrhizal fungi, which either wrap themselves around roots or penetrate the cells of root systems, receive part of the sugar produced by plant photosynthesis from trees as a source of energy.

In exchange, trees receive nutrients like phosphate and nitrate as well as water from the fungi in an unromantic marriage of convenience of sorts.

Dual symbioses expand habitat

Using more than 400 different tree species spread around the world as a basis, researchers at the University of Zurich (UZH) and Agroscope have shown that many of them have further improved this cooperation system.

Although most tree species form an association only with a single type of mycorrhizal fungi, "some woody plants form an alliance with two fungus types simultaneously," says Ido Rog from the Department of Plant and Microbial Biology at UZH.

The researchers now show that "bigamy" of this kind improves tree fitness, making trees less sensitive to drought and rendering them better able to cope with nutrient scarcity.

"They thus are able to colonize a much larger territory than tree species that form a symbiosis with only one fungus type can," lead author Rog says.

The broader geographical range and the expanded environmental niche space occupied by those trees are independent of their phylogenetic architecture and evolutionary history.

More resistant to heat and drought

The concurrent associations with two different mycorrhizal fungi enlarge the diversity of trees' nutrient supply because their roots cover a more extensive soil profile and are capable of coping with a more diverse range of soil properties.

"Our findings indicate that polygamy with two fungus varieties served as a strategy enabling trees to adapt to rougher environmental conditions and to thus colonize nutrient-poorer niches and endure harsher climates," UZH professor Marcel van der Heijden says.

So, the distribution of trees with dual symbioses is much more pronounced in dryer areas, for example, than in rainier habitats.

"In forestry, this knowledge could be helpful in the future for selecting tree species specialized in dual fungal associations because they are likely to be better at coping with ongoing global warming and could be used to colonize dry climate zones," van der Heijden explains.

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Journal Reference:

1. Ido Rog, David Lerner, S. Franz Bender, Marcel G. A. van der Heijden. The Increased Environmental Niche of Dual‐Mycorrhizal Woody Species. Ecology Letters, 2025; 28 (5) DOI: 10.1111/ele.70132