How an invisible fungal alliance helps forests thrive

When you look at a forest, the variety of trees you see above ground is only part of the story. Beneath the soil, vast networks of fungi influence which trees thrive, which coexist, and how forests respond to the challenges of climate and geography.

A new study led by researchers from Purdue University and Peking University has revealed how these underground fungal allies shape tree diversity across the globe. Their influence varies depending on latitude, moisture, and environmental stress.

Fungi hidden beneath forests

Jingjing Liang, an associate professor of quantitative forest ecology at Purdue, co-led the study with Zhiheng Wang from Peking University.

“What we can see above ground is governed to a large extent by what is happening belowground,” said Liang.

The experts analyzed data from over 442,000 forest plots worldwide and focused on two main groups of mycorrhizal fungi: ectomycorrhizal and arbuscular mycorrhizal fungi.

Both form partnerships with tree roots, trading nutrients for carbohydrates, but they do so in different ways that profoundly influence forest diversity.

“The loss in tree species diversity may damage the ecosystem services provided by forests,” Wang said. “Understanding the mechanisms driving the maintenance of tree species forest diversity is fundamental for the conservation of tree species diversity.”

Solving a forest diversity puzzle

For years, scientists have debated how fungal partnerships impact tree species diversity, proposing three competing hypotheses. This comprehensive global study found that all three are valid, depending on environmental context.

“Our findings reconcile inconsistencies regarding how mycorrhizal symbiosis influences tree species diversity,” Wang said.

Using precise forest inventory data collected worldwide, the team applied advanced statistical methods to filter noise from complex ecological data, revealing hidden patterns.

“With this data, we were able to very accurately capture this relationship between different types of mycorrhizal fungi and forest tree species diversity,” Liang explained.

Fungal effects shift with climate

University of Michigan ecologist Peter Reich, a senior co-author, highlighted the value of the study’s comprehensive approach.

“This insight would have been impossible to detect without the comprehensiveness of this dataset, which allows us to test across large gradients of temperature, moisture, and latitude,” he said.

Reich explained that ectomycorrhizal fungi often dominate in cold, nutrient-poor regions that naturally have fewer tree species. Without a broad dataset, this dominance could obscure the fungi’s more nuanced effects.

“But by being able to tease apart temperature and moisture, we can see that when conditions are generally good,” he said. “The more abundant the ectomycorrhizal are, the more they do to reduce tree richness.”

The process is complex. While dominant tree species naturally suppress less competitive species, root pathogens usually check the dominance, allowing diversity.

Ectomycorrhizal fungi suppress these pathogens, enabling dominant trees to thrive unchecked, which can reduce species diversity.

Harder climates, stronger alliances

The study also found that under stressful conditions – such as low moisture or cold climates – the combination of both fungal types fosters greater diversity.

In these environments, resource-sharing partnerships help more tree species survive, while pathogen suppression plays a smaller role.

“Both ways of influencing tree diversity are real, but their relative balance and magnitude of impacts vary with environmental context,” Reich said.

Healing forests from below

Liang emphasized that understanding the hidden fungal networks in forests is akin to treating a patient holistically.

“We should not just look at the surface symptoms. We should look deep down, literally to the roots of the problems, and that is belowground mutualism,” he said.

This work, supported by the Global Forest Biodiversity Initiative and its Science-i platform, demonstrates how global collaborations can untangle complex ecological questions.

Forest conservation and fungal networks

The findings open pathways for further research: How do these underground alliances affect carbon storage in forests? Can fostering specific fungal partnerships enhance forest resilience in a changing climate?

 “And what can we do to enhance the health of our forest ecosystem by not just seeing what is on the surface, but what is belowground?” Liang asked.

By revealing the profound influence of underground fungal networks on forest diversity, this research underscores that the key to healthier forests – and perhaps a healthier planet – may lie hidden beneath our feet.

The study is published in the journal Science Advances.

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