Going underground

Amanda Barnes explores the extraordinary underworld kingdom of fungi and how it vitally supports the health of vines - and even what it means for flavours in wine itself.

Hand and soil

We often fall into the trap of only thinking of what is going on above the soil in terms of sustainability. It is easy to consider how vines are treated with sprays and applications, or be reminded of the flora and fauna that roam nearby, or the people that work among the vines. But there is another kingdom at work in the vineyard, one much harder to see, but just as vital — the network of fungi or mycorrhiza below ground.  

In recent years, understanding and respecting the fungi kingdom has become a hot topic in viticulture. As the health world becomes ever more obsessed with the health of our gut microbiome, viticulturists and winemakers are increasingly interested in understanding what is happening in the great microbiome under foot. It is beneath the surface of the vineyard where a complex kingdom of millions of microorganisms interact with the soil and vine roots. The ruler of this kingdom is fungi.  

A short warning: this article is going to get seriously geeky. Simply put, the fungi in the vineyard soil create a web-like fabric that interacts with the vine roots in the rhizosphere, the root system and region where minerals, macronutrients, water and carbon are exchanged in order to allow the vine to thrive above ground.  

This is where the fungi comes in… a healthy and prolific growth of this very fine web-like fungi works in symbiosis with the vine roots — a mycorrhizal association. The fungus colonises the vine roots, as arbuscular mycorrhizal fungi, allowing for a far greater and mutually beneficial exchange of elements. As deeply scientific as it sounds, most of the hard work is naturally done for us — the fungal kingdom is in charge. However, it is only more recently that winemakers have become more focused on respecting the underground kingdom.

Spade and soil

Emiliana, Chile’s first Regenerative Organic Certified® vineyard, has been firmly focused on initiatives to allow the vine’s microbiome to thrive. “In order to increase our biodiversity in the soils, we have 100% of our vineyards planted with different crops between the vine rows,” explains winemaker Noelia Orts.

“We plant different species of plants for their different roles. We plant radishes, for example, so that they bury and break into the soil creating a structure with more air so that more microorganisms can live underground.” When these plants dry out in the summer, they are then cut back and left in the vineyard rows in order “to feed” the microorganisms, Noelia adds. 

As well as diversifying the plant life above ground in order to increase populations of microorganisms underground, Noelia explains that this plant life plays a vital role in creating the ideal temperature below ground. “We have also found that these plants make the soil temperature much cooler — between bare ground and ground planted with cover crops, you can have a difference of 20C!” 

Soil temperatures are natural much higher than air temperatures, due to the soil’s ability to retain heat. Studies suggest that the optimum temperature for mycorrhiza formation is between 18-25C, which is why in summer months (when the air temperature alone can reach 35C) this cover crop plays a vital role in keeping the soils cool enough for the fungi to function. 

Emiliana has also been focusing on their compost to support the fungi. “We have been learning about compost for many years now and know how to make a really great compost, with a combination of grape stems, grape skins, straw and cow manure. The compost provides lots of nutrients which also supports all the fungi.” In addition, Noelia’s team adds a worm compost — a vermicompost. It is applied as a sort of ‘tea’ through the irrigation feed, further nourishing the vine microbiome. 

The communication of fungi is another fascinating topic, still shrouded in mystery although scientists are working to uncover the secret language underground. What we do know is that fungi understand and emit a wide range of chemical signals. “We have a study in our vineyard which shows that there is a 98% coincidence between the bacteria of the soil in our native woodlands on the estate, and the soils of the grape vine parcels close by,” explains Noelia. “This means that there is subterranean communication. These microorganisms generate these chemical reactions leaving available nutrients for the plants to take. All of this ultimately means that the plant is more self-sufficient in nourishing themselves.” 

A dialogue is also happening about the temperature of the soil. “The really fine roots towards the surface are the ones that detect the high temperatures and they are the ones that send the stress signal to the rest of the plant so that it closes its stomata. This is another reason why the temperature of the soil is so important.” 

Although we know that the underworld kingdom of fungi is essential to a healthy vine, does it have any impact on the wine? Noelia believes it does: “The result is that we get far more non-Saccharomyces yeasts on the grapes, which give us a much more complex wine,” she says. “We have been doing a study on this for over two years and in the vineyard we have found some non-Saccharomyces yeasts in our vineyard that are not identified on any other international genetic database… it means our terroir is unique, and it is fascinating to be working on the potential for microbiological terroir!” 

I did warn you this was geeky territory… If you are still following, you can let your inner geek celebrate because it seems we are just at the tip of iceberg when it comes to the power of the underworld kingdom and its impact on complex, delicious wines.  

Amanda Barnes


Amanda Barnes

Amanda Barnes is an award-winning British journalist and editor who specializes in wine and travel writing. She is an expert in South American wine and regions and a regular correspondent for international wine and travel publications (including Decanter, The World of Fine Wine and Wine Enthusiast). She is currently studying to become a Master of Wine and is author of the South America Wine Guide.

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