Fungi of Aotearoa

A curious forager's field guide

~ Liv Sisson, 2023

How fungi eat

Here are the main ways fungi eat. These help explain both what fungi are and what they do.

Decomposition

Saprophytic fungi, also called 'saprobes, are the classic decomposers. These fungi are the great recyclers of our planet. They break down dead stuff and turn it into usable nutrients and rich soils. They grow on dead or dying organic matter like leaf piles, old wood and distressed trees.

Parasitism

Parasitic fungi grow from a host. The fungi siphon off usable nutrients from the host, or even use the host itself for nutrition, sometimes killing it. These species are fascinating, spooky, and bad news if you're a beetle, an ant or a spider — lots of insects and animals are plagued by parasitic fungi. You may have even experienced it yourself. Ever had, for example... athlete's foot? Fungal pathogens that affect plants, like Myrtle rust, cause disease and also harm their hosts.

Mutualism

Fungi that practise mutualism form a relationship with a plant to secure food. And you've actually already learned about a very famous mutualistic relationship in this book — lichen.

Fungi are hard to put in a box, though. They rarely use just one of the feeding strategies described here. Their relationships are difficult to define and are almost never purely cooperative or purely competitive. Sometimes fungi share, sometimes they steal. Sometimes they help, other times they harm. These relationships ebb and flow. Collaboration, at the end of the day, actually requires cooperation and competition.

The Wood Wide Web

The strange, pale plant Monotropa uniflora shows us that nutrients can move from fungi to plant and from plant to plant via fungi. Almost no one has contributed more to our understanding of this than Suzanne Simard, a forest ecologist at the University of British Columbia. In 1997 she published a fascinating scientific study that illustrated just how complicated and intriguing relationships on the forest floor can be.

In the study, Simard exposed birch seedlings to radioactive carbon dioxide. Two years later she returned to the same patch of woodland and saw that the carbon had passed from the birch seedlings to nearby fir seedlings, which shared a mycorrhizal fungal network — but not to nearby cedars, which did not share the network. And when the fir seedlings were shaded, and their ability to photosynthesise was therefore limited, they received more carbon from the birch tree 'donors' than unshaded firs did. Simard showed that within the forest system, carbon moves from places of abundance to places of scarcity or need. This work challenges the idea that plants are distinct entities that only compete with one another. It suggests that rather than focusing on competing individuals, we need to look at the whole community to understand how a forest 'works'.

Information can also be shared via fungal networks. Simard and her colleagues planted Douglas fir seedlings and ponderosa pine seedlings next to one another, with mesh barriers in between. The mesh prevented the trees' roots from touching but allowed enough space for contact via mycorrhizal mycelium. The researchers then stressed out the fir seedlings by pulling off all their needles. The naked trees then sent a 'warning' signal through the fungal network to the pines, which produced protective enzymes in response.

Simard noted that fungal networks operate like neural networks in our brains, or even the internet. They move resources and information to places where they're needed, when they're needed. On the back of these studies, Simard coined the phrase 'Wood Wide Web' to refer to this sophisticated system that sits at the foundation of our forests.

Simard has also helped to paint a picture of just how buzzy and intertwined the world beneath our feet is — this world we cannot see. In a 30 square metre stand of Douglas fir trees, she mapped out exactly which trees were connected to one another. The most well-connected tree - the 'mother tree'

According to Simard, mother trees look after' seedlings in their network, providing them with extra nutrients as they struggle upwards from the noisy and hyper-competitive understorey. When these great old trees, the keeper of their system's 'memory', begin their long, slow death, they can dump their nutrients into the system and share their remaining resources preferentially with younger trees who are their offspring.

The Mycelial Market

The term Wood Wide Web is catchy and inspiring, but fungi do get a bit lost in there. Within the Wood Wide Web framework, fungi sometimes feel like a passive partner; just a pipeline. But if you look at things from the perspective of the fungi, things get really interesting. This is where the idea of the Mycelial Market comes in.

The Mycelial Market shows us another way to 'know' what mycelium is and what it does. Through this lens, fungi are not just silent middlemen - they are brokers on the forest floor who oversee deals big, small, good, bad, fair and unfair. Their relationships with trees are complicated — it's not one fungus and one tree, sharing equally. Far from it.

Toby Kiers, an evolutionary biologist at VU Amsterdam, sees the Wood Wide Web as a market economy rather than a social welfare system. In one experiment, she saw that fungi could dictate the 'price' of phosphorus. Kiers exposed one mycelial network to two phosphorus supplies - one plentiful, the other scarce. In the plentiful area, the 'price' that trees had to pay for the phosphorus was lower — let's say one unit of tree sugar for one unit of fungi phosphorus. Where the phosphorus was in shorter supply, though, the trees had to make a stronger offer, like two sugars for one phosphorus. The fungal network was also able to transport phosphorus to the area with the better exchange rate, to capitalise on demand. Sound a bit like your Economy 101 course?