Mycorrhizal Fungi, How Plants Communicate

Next time you are walking in a forest, woodland or just open countryside on undisturbed fertile ground consider that there is more activity and biodiversity below the ground than what you can see above it. Amongst the vibrant range of lifeforms is a mostly microscopic network of fungi. Fungi are a distinct kingdom from plants. The term plants includes trees. The mushrooms we see sprouting out of the ground are in fact the fruit of the fungi. Below the ground the fungal organism lives in the soil interwoven with plant roots as a threadlike hyphae fabric called a mycelium. The mycelium web expands creating a ‘mycorrhizal network’.

Mycorrhizal Network

This network connects individual plants and is used to transfer water, nitrogen, carbon, minerals and nutrients. It can be found in the top ten centimetres of soil and may go as deep as a meter or maybe more. The German forester Peter Wohlleben coined the term ‘wood-wide web’. It is through this wood-wide web that plants communicate. This is an electro-chemical communication similar to that inside human bodies.

The fungi connect to the roots and cells of plants by penetrating them or by creating a net around them thereby also protecting them from pathogens. This underground network is highly resilient as different species of trees connect to each other and to different species of fungi thereby gaining the ability to diversify their responses as necessary. Mycorrhizal networks are made up of thousands of fungal species.

In healthy and long established ecosystems, most, if not all, plants are connected to a mycorrhizal network. This is particularly critical for saplings growing where there is not enough sunlight reaching their leaves to perform adequate photosynthesis. The saplings rely on nutrients and sugar from older and taller trees. A study conducted by the Reading University, England on Douglas fir trees indicated that trees recognize the root tips of their relatives and favour them when sending carbon and nutrients through the fungal network.

Ecologist Suzanne Simard finds the relationship between underground fungal networks and plants to be motivated by both collaboration and self-interest. The mycorrhizal network plays a collection, processing and distribution role that keeps plants healthy in exchange for supplies of sugar and carbon. Trees supply the network with ten to thirty per cent of the sugar that they generate through photosynthesis. This sugar is a life-line for the fungi. The fungi in turn collect mineral nutrients such as potassium, nitrogen, phosphorus and other trace elements and delivers them to the plant roots.

Mycorrhizal Network

Trace minerals are spread out over large areas in the soil beyond the reach of most plants in sufficient quantities. On the other hand spreading out is what fungi do. There is a fungal network in the Blue Mountains of Oregon, USA that is ten square kilometres large.

Plants and fungi have a symbiotic relationship which is a way of saying that they established an intimate, long term relationship during which they are essential to each other for survival. Eighty to ninety per cent of all wild plants globally are in this symbiotic relationship. This collaborative co-existence helps maintain the dynamic equilibrium of ecosystems and distributes nutrients and defensive mechanisms across ecosystems wherever they are needed.

The special relationship between fungi and plants started evolving four hundred million years ago. Scientists have however started joining the dots and understanding its presence and implications only since the 1990s.

This fungal network also derives nutrients and carbon from rotting leaves and insects.

Swiss researchers have observed that some of the trees in a forest had not had new growth in thirty years and still looked green and healthy. Research revealed that the neighbouring plants were supplying them with nutrients and keeping them alive through the fungal network.

The older mother trees are the powerhouses of the forest and woodland systems and are the plants that have the most fungal connections. Their roots are established in deeper soil, and can reach deeper sources of water to pass on to saplings. The mother trees are able to detect distress signals from neighbouring younger trees and send them the necessary substances. This is one of the main reasons why the destruction of old-growth trees has a disproportionately negative effect on ecosystems.

Mycorrhizal Network

Plants and trees have preferences and have a more intense networking with members of the same or related species or with other species where mutual benefit is possible. Several studies show that Paper Birch trees, being deciduous and therefore losing their foliage seasonally, cannot photosynthesis in the season when they are without foliage. During these periods deciduous trees connected to the local mycorrhizal network, are supported through the fungal web by the Douglas fir coniferous trees that are evergreens. When the Paper Birch trees are taller and in foliage, they repay the debt to the Douglas firs.

The mycorrhizal network is a living highway that is not only used for mutual benefit. It is also used by stressed plants to alert the ecosystem of the presence of pests or pathogens; by certain plants to completely live off nutrients from other species without giving anything back; by dying plants to donate the remaining nutrients to their neighbours; by plants to disperse toxic chemicals to discourage unwanted neighbours.

There are striking similarities between the social order existing in wilderness and human societal norms and behaviour. This is not surprising as we are all children of the natural world.

This article was published in the Times of Malta on the 10 November 2021 How Plants Communicate

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