Capturing Carbon With Tasty Fungus

11:21 minutes

Two bright blue mushrooms, one showing the gills on the bottom of the mushroom cap and one face up with the top of the mushroom to the camera.
Lactarius indigo, the blue milk cap. Credit: Alan Rockefeller, Mushroom Observer /CC BY-SA

This week, a report from the Intergovernmental Panel on Climate Change brought dire warnings about our planet’s climate future and an alert that drastic action is needed—now—to avoid catastrophe. One action the report recommends involves an overhaul of our food production systems to decrease their carbon impact.

Three reddish brown mushrooms of the genus Lactarius growing in a green grassy area.
Mushrooms of the genus Lactarius share similar features with the Russula, in particular the brittle stems. They can, however, be distinguished from Russula by the milky or watery substance they exude when broken, especially around the gills and the stem attachment to the cap. Credit: Wikimedia Commons

Writing in the Proceedings of the National Academy of Sciences, researchers suggest one possible way of sequestering some carbon dioxide might be cultivating certain kinds of edible mushrooms on land that has already been cultivated for agroforestry.   The researchers are working with Lactarius deliciosus, commonly known as the saffron milk cap or red pine mushroom, but other species are possible as well. These  mycorrhizal fungi live in a symbiotic relationship with the roots of the trees, increasing biomass and storing more carbon, while producing food on land that might have otherwise been used only for trees.

In certain climates and with certain trees, these fungi can actually be a carbon-negative source of protein. However, to produce a pound of protein currently requires a lot of land and effort. The researchers are working to make forest fungal farming easier, and to expand the approach to a wider range of trees. 

SciFri’s Charles Bergquist talks with Dr. Paul Thomas, author of that report and research director at the company Mycorrhizal Systems, a company that helps farmers grow truffles. He’s also an honorary professor in the University of Stirling’s Faculty of Natural Sciences in the UK. 

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Segment Guests

Paul Thomas

Dr. Paul Thomas is research director at Mycorrhizal Systems and an honorary professor in the Faculty of Natural Sciences at the University of Stirling in Stirling, UK.

Segment Transcript

CHARLES BERGQUIST: This is Science Friday. I’m Charles Bergquist. This week, another report from the IPCC, the Intergovernmental Panel on Climate Change, brought dire warnings about our planet’s climate future and warnings that drastic action is needed now to avoid catastrophe.

One action the report recommends is an overhaul of our food production systems. Writing in the proceedings of the National Academy of Sciences, researchers suggest one way of sequestering CO2 is cultivating certain kinds of edible mushrooms.

Dr. Paul Thomas is one of the authors of that report. He’s research director at the company Mycorrhizal Systems. They help farmers grow truffles, and an honorary professor in the University of Stirling’s faculty of Natural Sciences in the UK. Welcome to Science Friday.

PAUL THOMAS: Thank you, Charles. Thank you for having me.

CHARLES BERGQUIST: So I’ve seen commercial mushroom farms, especially for things like the standard white button mushrooms that you find in supermarkets, but that’s not what we’re talking about here.

PAUL THOMAS: Yeah, absolutely. So those mushrooms that you see in the supermarket, they’re what we call saprotrophic mushrooms, so they grow off a degrading plant matter, so they’re quite often grown indoors on plant matter, and actually, they use a lot of peat as well in the production of those mushrooms, so they grow in a very different way to the ones that we’re proposing.

CHARLES BERGQUIST: So the ones that we’re talking about now, are these kinds of fungi that people might have encountered before if they’re not a forest forager of some kind?

PAUL THOMAS: Yeah, so these kind of mushrooms actually, there are some species which they may have encountered in restaurants or on supermarket shelves. They include things like chanterelles, or puccini, or king billets. Those are all in this same category of fungi, but normally, they’re not ones that you often find on supermarket shelves, or often in the restaurant, or most specialist places.

CHARLES BERGQUIST: As you mentioned, there are types of fungi that live on rotting wood, and you can even buy those kit logs inoculated with spores if you want to do that at home, but the ones we’re talking about, these are somehow living with the trees in a symbiotic relationship.

PAUL THOMAS: Yeah, absolutely. So they’re what we call mycorrhizal mushrooms, and what that means is they grow in– yeah, in symbiosis, in partnership with a plant host. And for this group of fungi we’re focusing on here, they grow with woody plants, and what they do is they cover the root system of the tree, and they form an association with that tree called the mycorrhiza, and it’s basically to facilitate the transfer of nutrients and resources, and it creates a big surface area to do that. So like our lungs have a very big surface area for gas exchange.

For the fungi, they create a very big surface area interaction with the tree so they can provide the tree with nutrients. And in return, the tree sends the fungus sugars because the fungus can’t access sugars on its own. So there’s this trade of resources, and they help the tree to grow, the tree helps the fungus to grow, and yeah, it’s a completely symbiotic association.

CHARLES BERGQUIST: You have a company that helps people to set up their own truffle farms, so you have a vested interest in this idea of trees and fungus. Are there places that are already doing this beyond truffles, other types of fungus?

PAUL THOMAS: So I absolutely started with truffles because I became obsessed with the research and the science. I just thought was mind boggling, and we’re looking at applying that technology now elsewhere to use it for other challenges. This kind of technology is being used by a number of researchers, so there are a few groups working on this.

It’s very small, but there’s a handful of people worldwide who are really focusing on it, and most of the progress has been made with a group called lactarius, or the genus lactarius, and they produce a mushroom called the delicious milk cap. Lactarius delicioso, which has got a great name, and obviously hints towards that it’s quite a palatable species, but it’s one that we can produce.

So we can get the mycorrhiza growing on the root system, and it will produce fruiting bodies, sometimes as quick as just 18 months. But what we’re looking at doing to follow on with this project, we want to screen a large number of species and get many species which will grow in different bioclimatic conditions.

CHARLES BERGQUIST: What are the mechanics here? How do you plant the fungus, so to speak?

PAUL THOMAS: Yeah, so it’s different for different species. So some of these mycorrhizal fungi, it’s very hard for us to get them to associate with the tree, and there’s a role for different bacteria, and probably also different fungi in some cases, which all need to be there to form that association. For some of the others, we can use spores. So you can use the cap of the mushroom, grind it up, introduce it to the root system.

And then for others like this lactarius species I mentioned, spores don’t work for some reason we don’t fully understand, so we have to take a piece of the fruiting body and grow it on agar in the lab, so we grow in Petri dishes.

And then when that fungus is growing healthily and happily, we put it in close proximity to the root system of the tree under sterile conditions, and then it forms this mycorrhiza. And in the case of that species actually, it’s this beautiful orange mycorrhiza, and then we can plant that into the field to produce these mushrooms.

CHARLES BERGQUIST: I’m trying to get a sense of scale here. How much edible fungus can one tree produce?

PAUL THOMAS: There’s been very few trials done on this. Some of the trials that have been done, the production figures round about on a hectare basis, which is 100 meters by 100 meters, or 2.47 acres if you work in acres, produces about 1,000 kilos to 3,000 kilos seems to be about the productive range.

But that’s very small data set, and I’m sure with different species and different techniques, we can produce more than that, but we did our analysis based on the lower end of that spectrum, based on producing 1,000 kilos per year per hectare. So it’s a very small volume for the land use area, but even so, if we combined it with current forestry activity that’s occurred over the past 10 years globally, that would be enough to produce enough food output to support 18.9 million people annually, which is huge.

And for China alone, that would be 4.6 million people annually, so it’s– the idea is to use current forestry activities, inoculate the trees with this mushroom, so we’re not taking up more land area for food production, and it also opens up more land area that we can reforest with trees, while still getting a food output from that land because there’s this conflict in land use globally.

CHARLES BERGQUIST: I see. The current paper addresses the sort of climate advantages of doing this. Tell me a little bit about that.

PAUL THOMAS: In the system, because we’re growing it with living trees, we’re planting young trees, so we’re planting new trees which have got the root system covered in this fungus. So as those trees grow, they sequester carbon.

They’re pulling it out the atmosphere, and as they’re doing it, they’re producing this food crop, so it’s one of the few food crops in the world where in production of the food, we’re sequestering carbon, we’re pulling it out the atmosphere, and providing some mitigation towards anthropogenically driven climate change. We compared it to nine other major food groups, and even our most efficient food group, which is the production of pulses and grains.

They still emit carbon in their production, whereas this fungus would do the opposite. When you inoculate the trees with these fungi, they can also sequester more carbon anyway in the ground than the tree growing on its own because you end up with a much larger area of biomass below ground, which is locking that carbon in. So it’s a way that we can pull carbon out the atmosphere, of course, through tree planting, do it on a bigger scale, but in doing so, also still got food crop from that land, so we don’t have to sacrifice forests for our food production.

CHARLES BERGQUIST: Right, but I mean, even given that, this does not seem like a very efficient means of producing food. I mean, inoculating individual trees that need a lot of time and space to grow.

PAUL THOMAS: Yeah, absolutely. What we really need to do is make this a really extensive, quick, cheap, easy system. So we can’t rely on sterile techniques where we need to involve laboratories. Our idea is to slot into current forester activity, so we can inoculate trees very cheaply, very quickly. And “cheap” is the key word really. It needs to be very cheap per unit basis so we can do this on a large scale over a large, large area.

And then in terms of land use, it is relatively inefficient. It’s more efficient than extensive beef production, but that’s quite an inefficient use of land anyway. So it is relatively land inefficient, but it has all these associated benefits. All the conservation, biodiversity, benefits we get with tree planting. You can have a timber crop at the end of the day, and of course, the carbon sequestration, so we should view it in terms of this plethora of benefits, not just how much food is produced per meter squared.

CHARLES BERGQUIST: How much carbon dioxide are we talking about when we’re talking about the climate benefits here?

PAUL THOMAS: So what we did is we looked at all forested areas in the world really. Soil different areas from the subtropics, to the tropics, to boreal areas, and we looked at different land uses, so whether it is primary forests, secondary forest, or planted forest, and the greatest potential is probably in boreal regions, where you can lock up maybe 12 tons of carbon per hectare per year, which is relatively high.

And then actually in the tropics, we showed that in some tropical regions, it could lead to an emission, so it might not have the same benefit. And the caveat to that is the data we used from it was from 637,000 satellite and light form data points, and what they do is they look at aerial images, and they work out the carbon flux of these systems.

And in the tropical regions, we were showing a net emission of carbon, but probably because there was so much deforestation in those regions that it was showing an emission overall. So it’s slightly complicated by the data set, but for sure, different environments have different carbon sequestration potential from 12 tons a hectare downwards.

CHARLES BERGQUIST: So we’ve been talking about this as one way of reducing a carbon impact, but how is climate change affecting fungi overall?

PAUL THOMAS: Like all biological systems, it’s a mixed story. So we see in Europe, for example, if we look at truffles– because I’ve done a lot of work on climate change and truffles– this year in Hungary, so Hungary produces a lot of truffles. Typically produces about 80 tons a year. Their production this year was almost nothing because of the extreme heat events in Europe, and we’re seeing this trend towards declining production because of increasing heat and increasing drought in Europe.

A number of years ago, we published a paper predicting this was going to happen and the extent to which it would happen, and it’s happening now, so a number of species are very vulnerable. Of course, it also means that other species can grow in areas they couldn’t previously because the climate’s got slightly milder, so they can exist in that climate now, and that’s been the case in the UK where we can grow Mediterranean species now, which we couldn’t have done before the Industrial Revolution.

So there’s this change in boundaries, and there’s this vulnerability, but we’re in for some big challenges. I think some big challenges.

CHARLES BERGQUIST: You call the specific species that you’re looking at the delicioso. Are they particularly delicious?

PAUL THOMAS: Yeah, they’re great. They’re great. I really like them, and there’s a related species actually that grows in the US, which is bright blue, which is even cooler, lactarius indigo, and we did a paper on that a couple of years ago, but they’re really good, tasty mushrooms. Yeah, they’re delicious. Everyone should be eating them. Hopefully, we’ll get there. Yeah.

CHARLES BERGQUIST: Dr. Paul Thomas is research director at the company Mycorrhizal Systems and an honorary professor in the University of Stirling’s faculty of Natural Sciences in the UK. Thanks so much for talking with me today.

PAUL THOMAS: Thank you. It’s been a pleasure. Thank you.

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