Trade tactics of plant-fungal networks made visible

By tracking florescent nanoparticles across plant-fungal networks, researchers discover that fungi cope with extreme resource inequality by transporting nutrients to areas where plant partners are willing to pay more. The researchers from the Vrije Universiteit Amsterdam reveal this in a publication in the journal Current Biology.

06/06/2019 | 4:29 PM

When faced with resource inequality across their complex networks, fungi increase trade with their host plants. But they do it in a way that improves their payoff: moving resources across their networks to where they potentially gain a better price from plant buyers. The research, led by Toby Kiers, Professor of Evolutionary Biology at the Vrije Universiteit Amsterdam, has implications for understanding how economic systems can, and have, evolved.

By developing a technique to tag nutrients with fluorescent nanoparticles of different colors, the team could track how fungi bargain with plants under different market conditions, including environments of extreme inequality. The findings are in line with a growing awareness of the complexity and sophistication of the earth’s oldest and largest subterranean market.

Fungi and the economics of inequality
The world’s resources are spread unevenly. Organisms in nature must evolve ways to cope with relentless variation in access to resources. But unlike trade deals employed by humans, the trade strategies between plants and fungi have been tested and shaped over hundreds of millions of years of evolution.

Plant roots form trade partnerships with mycorrhizal fungal counterparts: the plants provide essential sugars and fats to the fungal networks, and the fungi provide nutrients such as phosphorus in return. Like savvy traders on Wall Street, both sides employ cunning strategies to maximize gains. But what drives their flexible trade tactics remains unknown.

Shining a light on trade
Until now, studying resource exchange in these subterranean markets has been problematic due to difficulties in accurately tracking the spatial movement of nutrients. To overcome this, the team developed a technique to tag phosphorus with highly fluorescent nanoparticles, called quantum-dots. They then exposed the fungal network to varying concentrations of the fluorescing nutrient in different colors, mimicking patches of abundance and scarcity across an artificial landscape.

Using high-resolution video, the authors measured speeds of particles being transported across the fungal network, observing complex flow patterns towards and away from the root. They developed imaging techniques to quantify the transfers of these fluorescent nanoparticles into host roots, and used techniques with laser beams determine when and where the fungus stored the resources across the network.

Sophisticated fungal trade strategies
Toby Kiers was surprised by the sophistication and plasticity of the fungal tactics, which included resource hoarding under stable conditions; accelerated trading in areas of scarcity; and active resource transfer from rich to poor patches to improve trade returns. “There is a striking elegance to the way these complex fungal networks deal with exposure to resource inequality”, Kiers said.

Intriguingly, this behavior allows the fungus to realize the benefits of trade -whether it faces a difficult trade environment, or a relatively stable distribution of resources. Given that fungal networks can be meters long in nature, how they exactly can coordinate these trade strategies remains an open question.

Not much room for pity
Referring to a recent popular book ‘The Hidden Life of Trees’, she notes that underground partnerships are not as harmonious as some believe. “There is disagreement as to whether trees use the networks to send resources to dying trees, for example.” She adds: “Economics in nature doesn't leave much room for pity.”

Trade Futures
As a next step, Kiers’ team is primed to study how fungi deal with economic crashes in nature. By physically severing the fungal network in half, she can mimic a severe, abrupt loss of resources. Given the fungi-plant trade partnership has survived for over 450 million years, she hopes the results will hold lessons for long-term economic resiliency.

A purple hyphal network