Soil fungi could help us with global warming

It’s not enough anymore to simply cut back on the CO₂ we’re pumping into the atmosphere: to address climate change we need to reduce the amount that’s already present there. Though many strategies to reduce greenhouse gas (GHG) emissions are needed, soil carbon sequestration – a major part of the Australian Government’s plan for net zero emissions by 2050 – can make an important contribution.

The 2018 SCINEMA International Science Film Festival Best Documentary and People’s Choice Award Winner Grassroots follows a journey to bring one such strategy to the world: using fungi to remove carbon dioxide from the air and store it in agricultural soil. Almost four years since the film’s debut, where is this strategy now?

What is soil carbon sequestration?

Soil carbon sequestration works by removing CO₂ that’s already present in our atmosphere and then converting it to a stable form of carbon that can then be stored in the soil long-term. There are different approaches to achieving this, but the one covered in Grassroots explores using endophytic fungi to turn Australia’s vast agricultural land into our largest potential carbon sink.

“Soil is the largest terrestrial carbon sink on the planet, managed by the people with the most to lose from climate change; farmers,” said agronomist Guy Webb, featured in Grassroots, to Australia’s Science Channel in 2019. “We are hoping that our trials will show that it can be easy and economical for them to transfer carbon from the air and secure it in their soil.”

In the film, the strategy promised to be a quick, globally scalable carbon removal solution that also provided huge benefits to the growers implementing it. But how does it work?

How does carbon sequestration with fungi work?

The strategy is not unlike the already common agricultural practice of inoculating pulse and legume crops with Rhizobia bacteria that fix atmospheric nitrogen into the soil.

Instead, a farmer coats their seeds with a microbial inoculum before sowing. This coating contains melanised endophytic fungus, a type of symbiotic fungus that then grows in the roots of the plants after they germinate.

As the plant soaks up CO₂ from the atmosphere and produces simple sugars in the soil (in a process called photosynthesis), the fungi work to convert these into melanin – a complex and longer-lasting carbon compound. It’s deposited safely into tiny, compressed particles of soil called microaggregates where, once trapped inside, carbon is stable within the soil and can be stored long-term.

“Endophytic fungi potentially have a role to play, especially in converting carbon to more stable, melanised forms of carbon that will resist decomposition and stay in the soil longer, thereby enhancing sequestration,” says Dr Michael Crawford, Chief Executive Officer of Soil CRC, who has over 25 years of experience in research and science management in areas related to soil science.

However, not only do you get the benefits of climate change mitigation by removing excess CO₂ from our atmosphere, but soil conditions also improve when enriched with carbon – resulting in increased water retention, nutrient availability, and improved soil structure for root growth.

This is particularly important to Australian growers as agriculture takes place on land that faces challenges with soil quality and water scarcity. But how far has this technology come in the past four years? And is it close to being widely available?

What’s happened since Grassroots?

There have been some exciting developments in the four years since Grassroots was released. Progressing in leaps and bounds, the startup Loam Bio (previously Soil Carbon Co) has raised $50 million from investors since it was formed.

Co-founded by Guy Hudson, Tegan Nock, Frank Oly, Mick Wettenhall, and Guy Webb – names you might recognise from Grassroots – the start-up is based out of Orange in the Central Tablelands of New South Wales. They now employ more than 35 people across four different laboratories and 25 field sites in Australia and the United States.

Loam Bio has been busy researching which inoculum is best at sequestering carbon, taking thousands of fungal samples from all over Australia and sifting through a library of more than 1,500 microbes to put them to the test.

Using bioinformatic analysis to study the microbial genomes, as well as extensive field testing, they’ve also been figuring out which combinations of fungus and bacteria are the most optimal to go to market, so that the product that reaches shelves can be accessible to all farmers.

However, according to Crawford, there are many challenges that need to be addressed if endophytic fungi are going to be effective in practical farming.

“The comparison with inoculation with Rhizobium bacteria is relevant to an extent, but fungi have many critical differences to bacteria  – size, morphology, life cycle etc,” he says. “Success is dependent upon the ability to introduce live microorganisms into a soil environment that experiences an extreme of conditions (wet/dry, hot/cold, acid, sodic etc), and for that fungi to successfully compete for resources against the microorganisms that are endemic (and adapted to) that environment.

“Obviously, conditions need to be optimum for the endophytic fungi to be introduced successfully such that they survive and prosper. This won’t always be the case.

“More field trial results are required to determine the consistency of benefits, across a range of soil type, climates, farming systems etc. to better understand the feasibility of implementation. This is starting to happen.”

So, it looks like for now we’ll have to wait and see whether the technology can overcome these hurdles. Luckily, we might not be left waiting for long; In 2021 Tegan Nock, Chief Product Officer at Loam Bio, told ABC News that the company was aiming to have a product widely available on the shelves by 2023.

How does using fungi compare to other carbon sequestration practices in Australia?

According to Crawford, saying that endophytic fungi could singlehandedly avert global warming is hyperbole – there is simply no silver bullet when dealing with climate change. Instead, it’s important that we build a larger repertoire of practices, of which carbon soil sequestration with endophytic fungus could make up just one of many strategies.

“It is critical that research into technologies such as this continue, especially given the emphasis on a technology-led response to climate change,” says Crawford. “In reality, it is likely that practices such as melanised endophytic fungi will make a contribution to soil carbon sequestration, along with practices such as zero tillage, stubble retention, summer cropping, double cropping, perennial pastures, intercropping, removal of soil constraints etc, but it won’t be the sole solution.

“Irrespective of the climate change benefits, any practice that leads to higher levels of organic matter in the soil will also result in increased water infiltration and retention, improved soil structure, enhance biological activity and nutrient availability in the longer term, and will be good for soil health and farm productivity more generally.

“Which is a very good thing.”