Plants transfer massive amounts of carbon to fungi

It’s commonly acknowledged that Mother Nature has her own rules, proving time and again that she plays by her own playbook. And today, we’re diving into one such fascinating realm, which presents an opportunity to revise long-held scientific viewpoints on plants and fungi.

We often think of plants as stationary fixtures, hinged to the ground by their roots, twirling their leaves in sync to the rhythm of the wind. But plants, it seems, are silent movers and shakers, involved in a vast annual movement of carbon.

Remarkably, each year, they shift a whopping 3.58 gigatons of carbon to mycorrhizal fungi – their partners in the underground realms. For visualization’s sake, were this carbon a solid mass like ice, it would suffice to lay a slick sheet over 112 million NHL hockey rinks.

The market perspective

Previously, scientists, akin to economists, have viewed this hefty carbon transfer as a kind of marketplace transaction. The understanding was fairly straightforward – in this unique marketplace, carbon was traded for essential nutrients delivered by those fungi residing underground.

It seemed like an equitable exchange, neatly governed by market principles of trade. But, as it happens in the world of science, not everything is as it seems.

A team of researchers, including Professor Justine Karst of the University of Alberta, suggest we need to reassess how these eco-critical systems function.

The experts argue that market principles are not universally applicable, particularly not in the case of this unique plant-fungi relationship. “We found no evidence of trade,” said Professor Karst.

Link between plants and fungi

Mycorrhizas are essentially symbiotic relationships between plants and fungi that operate underground. The constant shuttling of resources between plants and fungi, seen as a hallmark in biological market models, is well established.

Herein, mycorrhizal fungi happily accept carbon in the form of lipids and sugars from their botanical partners, reciprocating with a supply of essential nutrients such as phosphorus and nitrogen.

However, this economic analogy has shrouded our understanding of mycorrhizas, according to the researchers. They argue that it might have made us blind to other possible functions of mycorrhizas.

An alternative perspective

An alternative theory titled the “Surplus C” hypothesis recently surfaced, proposing that plants often manufacture more sugars than they require for growth.

As per this theory, the excess carbon simply finds a home in the mycorrhizal fungi. This implies the volume of carbon handed over to a fungus isn’t dependent on the delivery of nutrients to the plant.

Leaning toward the new theory

The team’s comprehensive review of multiple scientific studies failed to produce convincing support for the biological market models.

The experts found no empirical evidence of a direct regulatory function and hence dissed the idea of “prices” – the ratio of carbon units to nutrient units – controlling the carbon handover to fungi.

Delving further into the mycorrhizal link, they discovered that plant growth was associated with nutrient uptake, not carbon transfer. Interestingly, what curtails plant growth is not the quantum of carbon sent to mycorrhizal fungi but the volume of nutrients delivered by the fungi.

It appears that the carbon handed over to mycorrhizal fungi is not costly for the plant. The research findings leaned more towards backing the Surplus C theory rather than the market models.

Rethinking relationships between plants and fungi

The researchers’ observations encourage us to set aside narrow economic models and explore the essential interactions between plants and mycorrhizal fungi.

According to Professor Karst, the key is in understanding the carbon flow from plants to fungi, given its potential in benefiting the environment – especially with respect to carbon sequestration.

The review also highlights the need for more targeted research to get to the heart of what determines the carbon transfer from plants to mycorrhizal fungi.

Finally, while a direct link between carbon and nutrient transfer may still be waiting in the wings to be discovered, the researchers caution against over-reliance on economic models to make sense of it all.

“The idea of markets is familiar to us, but the inner workings of mycorrhizas are not, so we need to stay open to other ways of understanding how these systems work,” said Professor Karst.

The study is published in the journal New Phytologist.

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