Underground symphony

Text by Rose Lengyel

Out of the blue

Underground symphony

Out of the blue

Underground symphony

Below ground, it is a web of interlacing roots teeming with life.

Underground symphony

A sea of chlorophyll, heaving with a multitude of lovely, fleshy grape bunches, all bluish-black and velvety… such is the tableau that spreads before you when you gaze over the vineyards of Palmer in the late summer. But what about below the surface, deep within the soil riddled with gravel? What does the other side of the vineyard look like, this underground universe as invisible and mysterious as it is vital?

“We force its roots to plunge deep by planting the vines densely, just one metre apart, or 10,000 vines per hectare.”
Sabrina Pernet — Technical Director, Château Palmer

It is often said that a tree’s root system is the reflection of its foliage, as if the surface of the soil were a mirror. Is this also true for the vine, which is not a tree but a creeper? “Not necessarily, because we limit its upward growth by pruning it like a bonsai, while we force its roots to plunge deep by planting the vines densely, just one metre apart, or 10,000 vines per hectare,” answers Sabrina Pernet, Palmer’s technical director. But the image of the mirror seems relevant to her in the functional sense of the term: the lustre of a ripe bunch of Merlot, Cabernet Sauvignon or Petit Verdot owes as much to the vine’s leaves as to its roots. On the one hand, thanks to photosynthesis, the foliage allows the vine to produce sugars, which are accumulated in part in the berries. On the other hand, the roots enable it to draw water and essential nutrients from underground – nitrogen, phosphorus and potassium, as well as trace elements such as manganese and boron. Of course, the roots also anchor the vine stock in the soil, helping it to withstand bad weather. And they act as a reserve of sap and sugars too, a crucial source of energy for the vine’s reawakening in spring.

On a parcel whose eighty-year-old vines were recently grubbed up, lies a majestic vine plant with impressive roots. It had doubtless been of a respectable age, which gave the root system time to become well established, deep-plunging, robust and drought-resistant. All of which, in turn, will allow to produce wines bristling with complexity, expressing the distinctive soul of this great terroir. The bark of the wizened vine stock is a shade between brown and garnet-red. In some places, its sinuous roots curl as tightly as corkscrews. Though in France, this is an American vine: since the phylloxera crisis in the nineteenth century, European grape varieties have been grafted onto American rootstocks, the only kind capable of resisting the sap-sucking aphid. Our imagination is easily carried away by the thought of this interlacing of roots, conjuring images of winding mountain roads, a psychedelic labyrinth, an intelligent network…

“Roots constitute a continuously advancing front line, with innumerable command centres, so that the whole root system guides the plant like a kind of collective brain – or a form of distributed intelligence – which, as the plant grows and develops, acquires information important to its nutrition and survival.” So writes Stefano Mancuso – Italian biologist and founder of the study of plant neurobiology – in his book Brilliant Green: The Surprising History and Science of Plant Intelligence.Every plant has tens of millions of root apexes which form an elaborate sensory organ that functions as a network, capable of exploring the land where they grow, and seeking out water and food and moving closer to it, just as they may move away from possible toxic substances and around obstacles.

In the terroir of Château Palmer, these seeker heads must navigate their way through the gravel, hence the tortuous appearance of the roots and rootlets. They will adapt to the nature of the soil in each plot, plunging more or less deeply to find what the vine needs, sometimes as far as five or six metres, though in the estate’s largest terroirs they are often content to descend only one or two metres to settle into the clayey gravel, which acts like a sort of sponge that provides water drop by drop, while the excess is drained away by the sandy gravel just below. “The roots of the grapevine are particularly adept at searching for the resources present in the soil,” Stefano Mancuso explains. “We know a lot about them, as they were one of the first plants to be domesticated by man. But we still know nothing about how they communicate and exchange with other plants and organisms in the rhizosphere.”

“How exactly is the vine – through its root system and the life teeming all around it – able to soak up the soil, and to express this soil? This question fascinates us,” confides Thomas Duroux, CEO of the estate. “Because it is fundamental: you can have the greatest terroir in the world in theory, but if there is no connection between the vine and its terroir through an efficient, living root system, nothing happens.”

“If there is no connection between the vine and its terroir through a living, efficient root system, nothing happens...”
Thomas Duroux — Director, Château Palmer

Ultimately, attempting to unravel this rooty enigma can only lead the wines of Palmer towards still greater depth, elegance and complexity. Hence the decision to co-finance the thesis of a doctoral student from the University of Rennes, Marine Biget, who is working to lift a corner of the veil on what is called the “microbiological terroir” of the vine, to understand better why certain parcels of the same estate produce great wines and others do not. The researchers from Rennes have advanced the hypothesis – which their study seems to confirm – that there are differences in the composition of each vine’s microbiota, i.e. in the specific blend of the various communities of microorganisms (bacteria, fungi, viruses etc.) which exist in all living beings. In the same way that we as humans harbour, among other things, the now-famous intestinal microbiota, plant tissues harbour a microbiota as well.

“We focused on the inside of the roots, because this is where the relationship between the microbiota and the vine is most intimate,” explains Marine. The roots of Château Palmer’s vineyards contain no less than 500 species of fungi – including mycorrhizae – and more than 1,200 species of bacteria. It is thanks to them that the vine is able to nourish itself, to “drink” and to withstand environmental stress and pathogens. Plants build their root microbiota “mainly by recruiting microorganisms from the soil. Therefore what is contained in the roots more or less mirrors what is contained in the soil, only less complex,” explains the researcher, whose highly innovative work is based on techniques developed in environmental genomics.

TO CONSIDER THE SOIL AS AN INERT SUBSTRATE – to be sprayed with herbicides and other pesticides whose function is to obliterate anything that is not “useful”, while the plant is fed with chemical fertilisers – is the hallmark of so-called “conventional” agriculture. “When I first arrived at Palmer, which was then still using conventional agriculture, I was struck by the manganese deficiencies in certain plots,” recalls Sabrina Pernet. “Since the château went organic and biodynamic in 2014, we no longer see that anywhere. Perhaps when you care for the soil with your own compost, and when you encourage an environment that is conducive to their development, the roots are enabled to take care of themselves.”

Today, all of Palmer’s vineyard practices are focused on a common goal: respecting the balance of nature and the vitality of the soil. That entails preparing “home-made” compost, prepared with a healthy dose of love, vine shoots from the vineyard, grape stalks from the harvest, manure from the estate’s cows and green waste from the upkeep of the estate grounds. It means spraying herbal treatments made from cow dung, nettle or calendula. And it also means growing cover crops between the vine rows, as well as wild plants and fruit trees. In the winter, sheep graze on the natural grassing and convert it into nitrogen, which is then left behind in the soil. The result? Microbial life, organic matter and soil oxygenation are further enhanced, which nourishes the plant and stimulates its own defences.

For now, these benefits have yet to be proven scientifically, beyond empirical observation. But this is also the purpose of Marine Biget’s thesis, which has established “that in bare soil there is less diversity of microorganisms that can be ‘recruited’ by the vine to resist certain stresses than in soil that is grassed over”. A second line of research asks: do biodynamic treatments provide additional microorganisms which help the vine to stimulate its defences, avoiding the need to fight diseases afterwards? Here again, the researcher realised that “the profusion of microbes in these biodynamic solutions is highly enriched in bacteria capable of producing antibiotics. It can be assumed that these organisms help the vine to cope with attacks.” The scope of enquiry is vast, and the secrets of the root system remain far from fully unveiled, with a multitude of questions still unanswered.

“Living soils help vines become more resilient in the face of climate change.”
Thomas Duroux — Director, Château Palmer

In the meantime, Thomas Duroux is already convinced: “Having living soils, and therefore a healthy and efficient root system, encourages a form of resilience in the vines in the face of climate change.” Trusting and respecting nature, even in its most tiny, subterranean, invisible forms...