June 15 2010 issue
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Rootstocks as an Element of Terroir Natalie Guinovart, CWE
Rootstocks are a vital part of modern viticulture; without them, the wine industry as we know it would not exist. But were wines actually better when all vines were grown on their own roots? It may be romantic to think that before the classic Vitis vinifera varieties were grafted onto phylloxera-resistant American rootstocks around the turn of the 20th century, European wines were more authentic. As Serena Sutcliffe, MW, attests, "They seem to have a different consistency in comparison to wines of today, with the ability to have an extraordinarily prolonged flavor."
Still, how much of that difference can be attributed to rootstocks, and how much is due to other factors such as vine age, developments in viticulture and viniculture, presence or absence of downy mildew, and the use of specific clones rather than field blends? After all, there are many examples of own-rooted vines today in regions unaffected by phylloxera, such as Chile, Argentina, and Australia, where the wines bear no resemblance to Sutcliffe’s description: "The scent from the empty glass that has contained a pre-phylloxera wine can be almost intoxicatingly ethereal." Are these modern wines less authentic in terms of terroir? In Sutcliffe’s opinion, "It would be difficult to say if pre-phylloxera wines showed more terroir difference than today’s wines as, when you taste wines that are now so very old, regional differences tend to be overwhelmed by all sorts of tertiary and other elements."
Although the relative influence of the various elements that make up terroir is often passionately debated, the use of the French word—whose Latin root means "earth" or "land"—implies that perhaps the answer lies beneath, where the roots soak up moisture and nutrients. While some regard terroir as only the soil, with its composition of rocks and minerals, terroir is actually much more than just geology; it involves all the natural elements that affect a vineyard site, including temperature, sunlight energy, precipitation, and topography. When we say we are tasting terroir, what we mean is that this particular combination of natural conditions has produced a wine with distinct qualities that could not be replicated elsewhere. The best expression of terroir tends to occur when vines are carefully tended and best suited to their particular site, and when the grapes are treated with a minimalist approach in the cellar.
EFFECTS OF ROOTSTOCKS ON SCIONS
Vine roots, whether original or grafted, communicate with the fruit-producing, upper part of the vine via the mutual translocation of nutrients, carbohydrates, and hormones, which act as growth regulators. These products are received in the requisite parts of the vine according to signals from climatic and soil conditions, such as temperature or water availability. The process of grafting a scion to a rootstock fuses two pieces of living plant tissue together, so that the vascular systems adjoin and the plant performs its normal functions. Rootstock varieties have different properties, just as vinifera varieties do, each with advantages and disadvantages (see box). Therefore, they are capable of modifying the vine’s natural response system—but does that technically distort the existing terroir?
Of all the elements that make up terroir, temperature has the greatest effect on wine style. Because each grape variety needs a certain total amount of heat to reach full maturity, some varieties perform better in warm climates and others in cooler ones. Early-ripening Pinot Noir has a lower total heat requirement than Cabernet Sauvignon, which needs warmer temperatures to be successful. Using a rootstock that favors early maturity can reduce the total heat requirement of the vine and thus can be helpful in a marginal climate where vines struggle to reach complete ripeness. This impact is small, however, and cannot make up for poor site suitability. In other words, Cabernet Sauvignon grown in too cool a climate will still be disappointing.
Rootstocks vary in their production of the natural hormones that regulate growth and vine physiology. One of these, abscisic acid, can have a critical effect on wine quality. ABA is synthesized when the vine experiences heat or water stress. Because it partially closes the stomata, the vine’s natural reaction is to concentrate its efforts into ripening fruit rather than growing shoots, theoretically improving quality. Drought-tolerant rootstocks such as 110 Richter have been developed with ABA production in mind. They have more efficient rates of transpiration and even encourage the production of fewer and smaller stomata, which is useful in drought-prone regions. But rootstock selection is not the only means of manipulating ABA. An irrigation technique known as partial root-zone drying tricks the vine into thinking it is in water deficit: abscisic acid is activated, shoot growth comes to a halt, and berry concentration kicks in. If rootstocks distort terroir, then irrigation techniques do, too.
A common trait of the best terroirs is low vigor. Vigor is influenced by, among other things, the amount of nutrients available in the soil, especially nitrogen and phosphorus. The capacity of a rootstock to absorb these nutrients will affect vine growth and berry development. The use of devigorating rootstocks can help limit yield, improve quality, and, ultimately, permit a more intense expression of terroir. Even in the virtually phylloxera-free Leyda Valley of Chile, winemaker Francisco Ponce of Viña Garcés Silva says, "We are not using rootstocks in order to adapt to different pH or nematodes. It’s only oriented to control vigor." The estate’s wines, despite being made from relatively young vines, reflect their terroir beautifully, with a natural minerality and a lively spark to balance their immense concentration. Garcés Silva doesn’t have to use rootstocks, but does so in an attempt to achieve greatness in its wines.
Mineral uptake determines more than vine vigor and depends on more than just the root system. Vinifera varieties accumulate minerals differently, and there are indirect effects on mineral absorption from mycorrhizal associations. Climatic conditions can also alter mineral content; for example, higher rates of transpiration (commonly seen in warm, dry conditions) are associated with higher levels of potassium, which can result in wines with higher pH and generally lower quality. Viticulture has an effect, too. Canopy-management techniques such as leaf stripping and vertical shoot positioning reduce shade and expose fruit to sunlight, lowering potassium levels. A winegrower in a warm, dry, sunny climate such as Chile’s Maipo Valley can leverage viticultural techniques to help keep potassium levels in check and thus improve wine quality without relying on rootstocks. Neither application is wrong, and neither distorts terroir; rather, they magnify it.
As I discussed this theme with winegrowers from around the world, in both areas that have phylloxera and those that do not, it became apparent that the relationship between rootstocks and terroir is a question not so much of science as of philosophy. Claudio Mestre, who oversees vineyard operations for Bodega Escorihuela in Mendoza, Argentina, believes that "vineyards that have own roots express the terroir totally, and nothing disturbs that transmission."
But if the wine isn’t any good, terroir is irrelevant, argues Eric Pooler, winegrower at DeLoach Vineyards in Santa Rosa, Calif. "Planting a vine on its own roots may indeed provide the best reflection of the conditions present within a given site," he says, "but this won’t necessarily result in the best grapes from this site." He finds that the expression of terroir is maximized by "farming practices that limit our need for outside inputs by enhancing the diversity of life within our vineyards. Through organic and biodynamic techniques, we are able to avoid pesticide, fertilizer, and other additions that may mask the natural expression of our site through our vines." Rootstocks are merely a factor in the equation, in his view: "Matching the correct rootstock to the correct conditions should be recognized as a part of terroir. If the terroir includes soils with high magnesium, for example, and the characteristics of the scion don’t tolerate this condition, fruit quality won’t be maximized by own-rooting."
Pierre Vincent of Domaine de la Vougeraie, who crafts magnificent, terroir-driven wines from an array of grand cru sites in Burgundy, also believes in biodynamic farming to achieve the purest expression of terroir. Like most French vignerons, he emphasizes the importance of soil quality. "The role of any roots is to absorb minerals in the ground," he says; "thus, I do not think that it changes fundamentally the typicity of terroirs." Who could argue that the best wines of Burgundy lack typicity or terroir? These vines are all grown on rootstocks.
In Neuquén, Argentina, another area where phylloxera is not an issue, winemaker Leonardo Puppato notes that Familia Schroeder is the only producer in the valley to have planted over to rootstocks. He estimates the extra cost to be $3.50 per vine; at a density of some 10,000 vines per acre over a total of 300 acres, that really adds up. Puppato believes that the long-term benefits will outweigh the initial investment, due to the effects of nematode infestation on both yield and quality. Other wineries in the region have maintained that nematodes are not a concern. On my recent visit, however, Familia Schroeder’s wines were the most refined, balanced, and interesting wines I tasted and seemed to best reflect the unique conditions of the Patagonian terroir.
MARKETING VERSUS TERROIR
In today’s saturated market, you’ve got to distinguish yourself from the competition. Trumpeting own-rooted vineyards in a wine world affected by phylloxera is one way of establishing an image, particularly at a time when perceived authenticity may offer a commercial advantage. Unfortunately, some of the producers who cite a connection between original roots and authenticity tend to make wines that do not resonate with terroir. These commercial wineries, by and large, do not practice organic farming or minimize intervention in the cellar. Their wines from large "single-vineyard" plots of overripe fruit are overextracted, flabby, and generic-tasting, with high levels of alcohol and too much new oak. They may be good, marketable wines, but authentic they are not.
Clonal selections, yeast strains, canopy management, and oak programs all have the ability to either muffle or amplify the voice of terroir, regardless of whether a vineyard is on its own roots or grafted onto rootstocks. Unsuitable rootstock choices can also mar the expression of terroir. Rootstocks can’t compensate for poorly drained soil or a gloomy, sunless vintage, but when selected appropriately, they can help vines achieve balance and produce exquisite fruit. Like proper site selection and judicious irrigation, rootstocks can help maximize quality and provide a conduit for terroir. But where terroir is not exceptional to begin with, or where farming or winemaking practices are not conducive to its enunciation, rootstocks are inconsequential. The ability of the roots to work in harmony with all the other natural elements is essential to the expression of terroir.