Grapevines are more drought-tolerant than thought

The latest word on the grapevine is promising.

During more than a decade of observation, grapevines in Napa, Calif., and Bordeaux, France, never reached lethal levels of dehydration from seasonal drought, researchers report online January 31 in Science Advances. Plant ecophysiologist Guillaume Charrier, at the French National Institute for Agricultural Research in Paris, and colleagues have determined just how resilient the plants are.

Grapevines lost most of their leaves only when their ability to circulate water and nutrients was reduced by 50 percent, due to lower water pressure in their stems and roots. While field conditions never led to water pressures this low, the team found the threshold for leaf loss in greenhouse tests.

Typically, when plants become extremely dehydrated and water pressure drops, air bubbles can develop in the xylem, tissue that carries water up from the roots (SN: 05/14/16, p. 32). In plants, as in humans, an air bubble — also known as an embolism — can prove fatal because it stops the transport of nutrients and can cause leaves to drop.

The team used a technique similar to a CT scan to “look within the stems of grapevines with X-rays without cutting into them” and see if embolisms formed, Charrier says.

Grapevines sacrifice peripheral parts, such as leaves, to preserve water pressure and avoid fatal embolisms. Different grapevine varieties, like Syrah and Grenache, were all similarly resilient, the team found.

“Before, we didn’t have an understanding of … how far we can push these plants until they die,” says study coauthor Paul Skinner, a soil scientist and vineyard consultant in Napa. Knowing grapevines’ response to dehydration could prove crucial as droughts become more severe with climate change. That could help vineyards conserve water with better irrigation strategies, and give wine connoisseurs something to toast.