The deep roots of terroir

Dienstag, 14. November 2017 - 9:45

Jungle roots/DirkvdM

Until recently, a forest was considered “a large area dominated by trees”, as Wikipedia puts it, as if it were just a patch of land sprouting plants. But new research has shown that forests are, in fact, super-organisms, whose individuals are connected to one another by their roots. 

Professor Suzanne Simard from the University of British Columbia has detailed how trees use the mycorrhizal fungi on their roots to pass information, nutrients and water to one another. By communicating through the mat of fungi under the forest floor, trees warn each other of insect attacks, pass on nutrients, and even nurture seedlings. It’s a phenomenon that’s been dubbed ‘the wood wide web’ and it’s crucial to forest health.

There’s more. In The Hidden Life of Trees (2015), Peter Wohlleben discusses research that suggests beech trees in undisturbed forests synchronise their photosynthesis. “Whoever has an abundance of sugar hands some over; whoever is running short gets help,” he writes. “Once again, fungi are involved. Their enormous networks act as gigantic redistribution mechanisms. It’s a bit like the way social security systems operate to ensure individual members of society don’t fall too far behind.”

Could something similar be happening below ground in a vineyard? If so, could it explain why some vineyards produce exceptional grapes?

The vine web
Associate Professor Miranda Hart from the University of British Columbia Okanagan studies soil biodiversity, to better understand soil microbial communities. She says there’s no reason vine roots shouldn’t communicate through their fungal networks, as grape vines are “highly mycorrhizal. The fungi that I study associate with almost everything out there, but grapevines particularly depend on them.” Do they also exchange information and nutrients? “Yes, all the time.”

What about the idea that some vineyard soils might be in such poor shape, that they’re effectively sterile? Meaning that the lines of communication are disrupted. Dr Hart says this isn’t likely, though she adds that “soil biodiversity is definitely suppressed in conventional agricultural systems”.

Yet even vineyards treated with herbicides and fungicides contain distinct microbial communities. “We’re only just learning about this,” she says. “Until recently, we thought microbes were the same everywhere in the world, but now we have better techniques to study them and we know they vary regionally.” Significantly, different microbial communities will cause “plants to express genes in different ways”. Theoretically, then, the same vine clone could express itself very differently depending on where it was planted, not only because of the soil and microclimate, but also because of its microbiome.

“Microbes stimulate plant defence mechanisms,” adds Dr Hart, explaining that this is particularly important for wine grape vines, because the “flavour chemicals that people are excited about – the flavonoids and antioxidants – are secondary metabolites,” produced when plants experience stress. “So I don’t think it’s a question of if fungi are important for terroir; we need to understand how they are.” She says that while researchers have been diligent about exploring abiotic stresses on vines (such as water deprivation or salinity), “we’ve ignored the biotic stressors,” such as those induced by microbes. “Plants have a very elaborate immune system and they’re either deterring herbivores or creating antimicrobial agents,” and the chemistry of that is very important to the grape’s sensory profile.

Teasing out the relationships won’t be an easy task. “We know that plants are connected to mycorrhizal fungi and we know they’re exchanging nutrients, but we don’t fully understand the relationship, because a lot of the time it’s not beneficial to the plants.” 

Terroir in a jar?
Do specific rootstocks – Dijon clones, say – come with specific communities of microbes, regardless of where they’re planted? Dr Hart says plants acquire microbes from the environment they’re in, so the “same rootstock in five different places would culture significantly different communities”.

Even so, will the day come when an enterprising microbiologist could create a ‘terroir kit’ to mimic the great terroirs? “It’s complicated,” replies Dr Hart. “Companies are trying to profit off these kinds of ideas, such as making specific microbes as growth enhancers. I don’t know about terroir enhancers, but we’re getting closer to identifying which microbes can elicit specific chemical production in wine. Whether or not you can ‘compose’ artificial microbial communities from this information is dubious.”

The mere idea bothers her. “We know how invasive species have destroyed so many ecosystems. It’s a risky proposition.” In any case, when it comes to the fungi which live on vine roots, it’s “much more beneficial if they have co-evolved. My research shows that commercial inoculants are almost unequivocally bad for the plant.”

One thing is for sure: a vineyard is not just a place where vines grow, any more than a forest is just land with trees. And there’s still so much more to discover.
Felicity Carter

This article first appeared in Issue 5, 2017 of Meininger's Wine Business International. For more free articles, sign up for our newsletter.