There Ain’t Mushroom Inside It

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A Short Ecology Lecture

Just a quick one from me. A few days ago Mark linked to an essay about mycorrhizae on the BBC, “Friendly fungi help forests fight climate change.” Naturally I read it, and have a few in-line comments and excerpts to share.

A Brief Primer

If you have never heard of mycorrhizae, that’s not surprising. But you will have seen mushrooms and toadstools: some of these are the fruiting bodies of a certain kind of mycorrhiza, “ectos.” Ectomycorrhizae. (Hard name to remember? Not really. Ecto, outside, mycor, fungus, rhiza, root. Fungus that lives outside the root. Geddit? There are “endos” too, which…. you guessed it.

Fungi come in a variety of forms, many of which we encounter day to day, sometimes without realising quite what they are: yeast that makes bread rise is a unicellular fungus. The black pin mould that later causes the demise of the same bread is also a fungus. Dry rot* is a fungus, and so is athlete’s foot. Those fungi with large obvious fruiting bodies we call mushrooms and toadstools get their carbohydrate in a variety of means – from consuming dead wood to destroying living wood (honey fungus as a good example) to actually getting a tree to give it to them in exchange for inorganic soil nutrients.

Ectos are in the latter group. They surround tree roots and set up with them a little swap shop. Who brings what? What does each party want?

Well, the tree has an excess of simple carbohydrates and is wanting nutrients like phosphorus. The ecto has access to plenty of soil phosphorus via its vast network of hyphae. It could of course engage in chemical warfare for what it wants, via the production of destructive enzymes. But a mutualistic enterprise seems to work better in some circumstances.

Figure 2-1 from Jackson & Mason 1984

A classic ecto is fly agaric, a familiar toadstool to anyone who has set foot in a woodland or watched Fantasia.^ According to wiki, this either gets its name from its use as a primitive insecticide, or owing to the fact that if you eat it your mind feels as if it is full of bluebottles. And contrary to good sense, people do actually eat it. Wiki describes its use as an “entheogen,” not a term I had heard, but you can guess what it means by its parts and their use in other words. In a perhaps overenthusiastic attempt at recycling, some folk would drink the urine of those who had earlier eaten the fly agaric. My question: did they take it warm, or let it get cold first? (I cannot abide clearing up warm cat sick, so whenever one of our furries has an accident, I cover it with a paper towel and wait for it to go cold first.)

The Essay

So with that as a primer, with some perhaps interesting but non-essential info added, let us move on to the essay itself.

Its second sentence is:

While we know that forests play a major role in countering global warming – acting as reservoirs for carbon – what is less well understood is how tiny organisms that dwell hidden in the soil help lock away our greenhouse gas emissions.

Here I would like to draw your attention to the way this is put. The use, or perhaps misuse, of active verbs immediately set my teeth on edge. Do forests counter global warming? Do soil organisms help to lock away carbon? If these things happen (and see below for a discussion about that) they have no beneficial intent. They have no intent at all, save to reproduce. That is ecology lesson #1. Nature has no motivation. It is callous, indifferent, ruthless, red in tooth and claw, amazing, beautiful, etc. Nothing that Nature does is for us.

Trees photosynthesise, and:

This is how trees naturally combat the planet-warming greenhouse effect. In the last 20 years, the Amazon rainforest alone is estimated to have taken in 1.7 billion metric tons of carbon dioxide.

Trees combat the greenhouse effect? No. Trees just rollin’. Is that 1.7 billions tonnes a real figure? I don’t know. In any case, is it net? Let us also in passing note that the Amazon rainforest has about the hottest average temperature on the planet.

Trees though do not act in isolation; they are entangled with – and work alongside – a vast community of micro-scale fungi.

A 2016 study led by researchers from Imperial College London revealed that one particular type – ectomycorrhizal fungi – enables certain trees to absorb CO2 faster (and therefore grow faster) than others. This is known as the “CO2 fertilisation effect”.

Aha, now in come the ectomycorrhizae. Unfortunately the association described was known about decades before this Imperial College study. It was discovered long ago that trees grown without their ectos – er, well, they didn’t grow. And when I say long ago… I mean 1917, roughly a century before 2016. This was when Melin discovered that seedlings of pine and spruce in newly-drained bogs only grew normally in the presence of ectomycorrhizae. Naturally, this discovery transformed the practice of forestry. But it didn’t happen in 2016.

The CO2 fertilisation effect, meanwhile, has nothing at all to do with ectos, and everything to do with the higher concentration of CO2 in the atmosphere making it easier for plants to photosynthesise.

Ectomycorrhizal fungi have also been found to slow down the process of rotting; decomposition breaks down all that locked-away carbon and releases it into the atmosphere. So the fungi, in effect, have two methods of fighting global warming.

I have no data on this, but it seems unlikely. It might refer to the fact that a symbiotic relationship is better for the tree than a pathogenic one.

Now is perhaps the moment to mention that decay in woodland is generally rather fast. Certainly litter does not survive long, hardly even from one autumn to the next. In the absence of permanent waterlogging or desert-level dryness, wood will also be devoured in a handful of years. What this means is that unless the above-ground biomass is increasing, there is no net fixing of carbon going on. In other words, a growing plantation fixes carbon but a mature forest does not. Of course, if you cut down the plantation, turn it into pellets and burn them, you can hardly say that a plantation fixes carbon either. The only way this can happen is if you make permanent use of the wood (e.g. by making it into a table). Probably sinking logs to the bottom of the ocean would have a similar effect.

Research conducted into planting one particular variety – Arbuscular mycorrhizal fungi, or AMF – in soil has shown how it can not only help enrich soil fertility, but also reduce CO2 levels in the atmosphere.

OK, so consider a modern farm: what sort of thing do we spray on the farm or coat our seeds with… well, fungicide to name but one thing. Kill them mycorrhizae thar! Oh, and pour a load of PNK over the soil to make it easier for the plant to get these nutrients, so they don’t need the symbiosis anyway. This much is obvious. It is not obvious to me how this would reduce CO2 levels in the atmosphere, unless the writer is referring to the reduced production of fertilisers.

Research has also shown a link between the loss of soil fungi and a reduction in carbon content of forest soil. Meanwhile, deforestation, which annihilates the fungi along with their host trees, disrupts this whole underground, climate change-fighting ecosystem.

Climate change-fighting ecosystem? (Picture me making a sour expression here.) As I have just explained, mature forests are not a carbon dioxide sink. Gone are the halcyon days that gave rise to the coal measures, because there are now saprophytic fungi that gobble up fallen timber as soon as it hits the ground.

These fungi might be tiny and hidden beneath the ground, but they form a network that is protecting our planet. Scientists who study them say we can do more – particularly through sustainable farming methods – to protect them.

Well, the fruiting bodies are not hidden, except for truffles. [Unlike fly agarics, the spores of truffles are not wind-dispersed. They get about thanks to the efforts of things like wild boar. Truffles are, however, ectos.]

As to the idea that any “protecting our planet” is going on, well, it’s erroneous.


A+ for the essay, simply because the author is only 14. Were she 41, the mark would have been C-.

The idea that Nature is working for the benefit of humanity is as erroneous as the idea that climate change activists are working for the benefit of humanity. But at least in the former case, coincidental advantages sometimes result.

Notes and References

*The latin name of dry rot is Serpula lacrymans, which as I translate it means “creeping weeping one.” (It used to be called Merulius lacrymans, which sounds like it has something to do with crying blackbirds, dunno.) Anyway, this rather fine beast, once established on damp wood, is able to grow on even if the wood subsequently dries out, hence the common name. It makes its own water by digesting the wood’s long-chain polysaccharides and eventually “weeps.” Nemesis to humanity’s hubris, its destructive power seems to be unrivalled. There was an outbreak after World War 2, following (among other measures) the stopping up of ventilation bricks to prevent the ingress of poison gas. Insulation authoritarians beware.

^I read that Walt Disney sent a still of the ring of fly agarics in Fantasia (one such is the featured image) to Chiang Kai-Shek, inscribed “From Fantasia. To Chiang Kai-Shek – In admiration. Walt Disney.” This was back before Pearl Harbour, when the US was neutral-ish; what Generalissimo Chiang Kai-Shek made of the gesture, I don’t know, nor what became of the still.

Richard M. Jackson & Philip A. Mason (1984). Mycorrhiza. The Institute of Biology’s Studies in Biology no. 159. Edward Arnold, London. Available at

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June 24, 2022

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