Terroir and Other Myths of Winegrowing by Mark A. Matthews

Author:Mark A. Matthews
Language: eng
Format: epub, azw3
ISBN: 9780520276956
Publisher: University of California Press

FIGURE 33. THE TRANSITION FROM HUMUS THEORY TO CONTEMPORARY PLANT MINERAL NUTRITION. (A) In the Humus Theory, plants consume organic matter (humus) as food particles. (B) Today, we know that plants absorb dissolved mineral nutrients from the soil solution. The mineral nutrients are derived from organic and inorganic sources in the soil, and the plant does not distinguish among the sources of those nutrients.

An Important Role for the Aerial Environment in Making Winegrapes

Once it is understood that berries are not made by a plant “eating” soil, the question “What makes a berry?” becomes more complicated—and interesting. A berry is comprised of about 5 percent “ash”—a catchall term for the incombustible mineral content derived from the soil. For plants to utilize essential soil nutrients efficiently, the additional factors of light, heat, and water must be adequately supplied. Some of those inputs are used in nutrient uptake, but most are involved in creating the rest of the plant (including the berry) using the products of the process of photosynthesis in leaves. Photosynthesis extracts carbon dioxide from the atmosphere (and releases oxygen) to create the building blocks of sugars, and from those amino acids and other compounds comes the stuff of berry growth and ripening. But recognizing this process was a long time coming. Andrea Cesalpino was a contemporary of van Helmont and an important early botanist, who, in De Plantis Libri (1583), claimed the function of the leaves was to provide shade for the rest of the plant (others thought the leaves might excrete waste). It was not until the 1700s that it began to be suspected that leaves might have a role in plant nutrition.

In Vegetable Staticks (1727), Stephen Hales demonstrated that plants absorb air, and suggested that plants derive nourishment from the atmosphere through leaves: “May not light also, by freely entering surfaces of leaves and flowers contribute much to ennobling principles of vegetation.” The roles of light, air, carbon dioxide, and water in photosynthesis were slowly resolved by the work of many European scientists. In 1780, the English chemist Joseph Priestley conducted a series of experiments that revealed that plants could “restore to a considerable degree of purity air that had been injured by the burning of candles.”63 The prevailing theory at the time was that flames are extinguished in airtight space because the air saturates with “phlogiston” (an imagined kind of bad substance). So, too, when a mouse was sealed in a jar, the air saturated with “phlogiston” and the mouse would weaken or perish.

Priestley placed a mint plant into an upturned glass jar of phlogistinated air for several days. He found that with the plant present “the air would neither extinguish a candle, nor was it all inconvenient to a mouse which I put into it.”64 Benjamin Franklin visited, and from experiments they conducted together, he noted, “We knew before that putrid animal substances, when added to the earth, produced sweet vegetables; and now it seems putrid air when mixed with plants similarly produce sweet vegetables.”65 By

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