New film captures mycorrhiza in motion for the first time

The story so far

AM fungi call plant roots their home, providing the crossroads between soil and plants. They scavenge essential minerals from the soil far better than plant roots can. The fungi trade these below-ground resources for above-ground ones: the plants’ supply of carbon, fats and sugars, gleaned from sunlight the fungi will never see. Often, the plants and mycorrhiza rely entirely on each other to survive.

The centre of this exchange are the arbuscules – branching tendrils that squirm and explore with a strange energy. It’s the arbuscule pulse that McGaley captured with her microscope.

The fungi have remained largely unchanged for the last 450 million years. Researchers now think the fungi were crucial for plant evolution: by acting as a root system, they gave algae a foothold to escape the sea. 

The relationship is so successful as to be ubiquitous. The fungi actually enter into plant cells, inflating a space like a water balloon, without killing their hosts. 

In some ways the relationship is like a mother and her child inside an amniotic sac, where nutrients can pass from one to the other across a membrane. Once the fungus leaves, the plant cells return to normal – quite how it manages to reorganise afterwards is a mystery.

Mycorrhiza in motion

In The Crop Science Centre, researchers are probing this mysterious life of plants. On each floor, you’ll find scientists zooming into plants at different scales. Some probe the machinery within cells, others focus on the larger structure of botanical bodies.

On her floor, McGaley has prepared a periscope for the underground.

After years of failed prototypes, she created a method that works: a 3D-printed chamber for the plant and fungi to call a home, with a window on one side. To peek in, McGaley uses a normal confocal laser-scanning microscope, but flipped upside down to unearth what usually lies below. 

By implanting fluorescent markers into specific plant genes, she can observe the flow of their inner lives without laying a finger on them. When McGaley beams a certain wavelength of light onto the plant roots, the markers illuminate and reveal themselves. She’s colour-coded the different transporters, so she can track how the fungus shifts nutrient passengers around the plant like London Underground lines.

What’s surprised McGaley is the diversity in AM fungi – both within individual networks and between species.

“We knew they were quite short-lived,” McGaley says. “Some don’t even last 8 hours. But when you observe different parts of one fungus, you can see some branches lasting 2 or 3 times longer than others. The whole process is completely dynamic – they never stop growing until they collapse.

“It’s almost like an apartment block of fungi occupying different parts of the root. The plant membrane divides these fleeting residents into their own compartments. Some of them will be better at taking up nitrogen, some phosphorus.

“My next goal is to time-lapse multiple species, and see how they interact within a plant root.”

Because AM fungi exist in such an unfamiliar world, we’ve neglected them for a long time. McGaley seeks to align the fungal timescale with our own, bringing their behaviour before our eyes.

“I love when people watch the films and say: it’s alive!” McGaley smiles. “If more people could see what was happening in the soil, they’d treat it better.”

It was an undergrad lecture from Professor Uta Paszkowski – Director of the Crop Science Centre – that first turned McGaley towards mycorrhiza. After her first summer lab working at the Centre, she was hooked. 

McGaley follows a rich history of fungi researchers at Cambridge – including Merlin Sheldrake (Clare 2007), whose bestselling book Entangled Life brought the public’s attention to the wonderful world of fungi. 

Cambridge’s current network of AM fungi researchers is thriving too, with nutritious connections in the Sainsbury Laboratory, the National Institute of Agricultural Botany (NIAB), the Botanic Garden, as well as other groups based in the Department of Plant Sciences.

A fungi-friendly future

Scientists are still uncovering the vital importance of AM fungi to our ecosystems.

It’s known that fungi can help plants become more drought resistant and increase their chances of survival in harsh conditions. But researchers also think that AM fungi play a crucial role in mitigating climate change, in their drawing down of atmospheric carbon into the soil. By some estimates, over a third of all human emissions end up in AM fungi’s networks. 

By accounting for fungal needs in restoration and plant breeding, we can increase our chances of success. If we overuse fertiliser, plants can over-rely on artificial means for their nutrients, and the plant-fungi symbiotic magic has no chance to get started. 

Elsewhere in the Cereal Symbiosis Lab, Dr Emily Servanté (Newnham 2015) is helping to test mycorrhiza-based bio-fertiliser, which could boost rice yields by 5 to 15%.

More widely, McGaley urges us to reduce our use of fungicides, artificial fertilisers and heavy tilling to ensure that AM fungi can do their work. The good news is that fungal spores are usually ready and waiting in the soil, eager to help the crops we plant. 

There are easy ways you can help fungi too: not disturbing soil, learning more at Plant Sciences’ community events, and keeping a wild and untidy garden would be a great start.

We are a long way from understanding AM fungi. Scientists are still figuring out how they integrate so much information over their whole network. We don’t yet know how they make decisions about where to focus their resources and which parts to grow. 

We also don’t know how the plants decide to end this relationship: if they keep tabs on whether the fungus is still offering a worthwhile trade, or if there are limits on how many nutrients can course through its roots. The line between being a parasite and a partner is constantly negotiated.

Finally, fungi challenge our core ideas of what it means to be an individual. Where is the boundary of the self in such a distributed but intermingled species?

In aiming toward such questions, McGaley keeps an open mind: “My method is to watch closely. We don’t know enough about these fungi to put them into a framework yet.”

Thanks to McGaley’s method, we can now watch what AM fungi are up to, and find better ways for them to flourish – for our mutual benefit.

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