Underland: A Deep Time Journey

by Robert Macfarlane

The term ‘mycorrhiza’ is made from the Greek words for ‘fungus’ and ‘root’. It is itself a collaboration or entanglement; and as such a reminder of how language has its own sunken system of roots and hyphae, through which meaning is shared and traded. The relationship between mycorrhizal fungi and the plants they connect is ancient – around 450 million years old – and largely one of mutualism. In the case of the tree–fungi mutualism, the fungi siphon off carbon that has been produced in the form of glucose by the trees during photosynthesis, by means of chlorophyll that the fungi do not possess. In turn, the trees obtain nutrients such as phosphorus and nitrogen that the fungi have acquired from the soil through which they grow, by means of enzymes that the trees lack. The possibilities of the wood wide web far exceed this basic exchange of goods between plant and fungi, though. For the fungal network also allows plants to distribute resources between one another. Sugars, nitrogen and phosphorus can be shared between trees in a forest: a dying tree might divest its resources into the network to the benefit of the community, for example, or a struggling tree might be supported with extra resources by its neighbours. Even more remarkably, the network also allows plants to send immune-signalling compounds to one another. A plant under attack from aphids can indicate to a nearby plant via the network that it should up-regulate its defensive response before the aphids reach it....