Merlin Sheldrake's new book “Entangled life: how fungi make our worlds, change our minds and shape our futures” has been published to great acclaim. As fungi live largely underground, we notice only fruiting bodies such as mushrooms and may not be conscious of the great extent and size of their underground webs. Sheldrake describes the world's largest living organism, Armillaria, a honey fungus in Oregon weighing hundreds of tons and extending over 10 hectares, between 2000 and 8000 years old.
Beneath a forest Sheldrake describes a “wood wide web”, fungal hyphae linking multiple varieties of trees and plants via connections with their roots. Signals, both electrical and chemical, may be passed from plant to plant, as well as nutrients given up to the plants, or fed back to fungi. Fungi express a great variety of olfactory molecules, for example the scent of truffles which attracts animals to eat them and spread their spores. It is attractive to speculate that there are grape flavours linked to the underground mycorrhizal web of individual vineyards, expressing a particular terroir.
Vine nutrition is enhanced by symbiosis between vines and arbuscular mycorrhizae. The fungi increase grapevine growth and nutrition by giving better access to soil nutrients and by activating uptake of phosphorus, nitrogen and other elements. They also protect plants from abiotic stresses such as lack of water, salinity, and heavy metal toxicity, and biotic stresses such as root diseases.
Grapevine root architecture is described as having relatively low density of large diameter fine roots, so that mycorrhizal fungi are highly beneficial by extending the volume of explored soil.
Junctions between vine roots and fungal hyphae are called arbuscules, where hyphae penetrate inside the roots, allowing reciprocal exchange of nutrients. There are two main families which may colonize vines, the Glomerales family which primarily colonizes roots from hypha, whereas root colonization from the Diversisporales family starts from spores. In the vineyard, both are profoundly affected by soil management techniques. A diverse collection of multiple mycorrhizal species provides greater benefit than having only one or a few species present. The variety of species associated with vine roots is affected by the range of plants in inter-row vegetation.
Out of sight, but not out of mind, vineyard mycorrhizae are an essential background to expression of vineyard terroir. Much remains to be learned, and for the moment we must consider minimizing disturbance of soil by cultivation, and provision of multiple symbiotic partners by encouraging a diverse plant population in the vine inter-rows.