Wine grapes in dry regions have a strategy to conserve water

In the near future, climate change is expected to make many grape-growing regions hotter and drier. Wine grapes are very sensitive to climate, which means it could become difficult to produce high-quality wine from traditional varieties. 

But now, a new study from UC Davis reveals that wine grapes from regions that are most susceptible to climate change have built-in defenses that may save them from rising temperatures. 

The researchers discovered that grape varieties grown in warmer, drier regions have traits that conserve water. This strategy evolved so that the vines have the water they need throughout the growing season.

Study lead author Megan Bartlett is an assistant professor in the Department of Viticulture and Enology at UC Davis. 

“The relationships between grape varieties and regions have historically been based on wine, without considering traits that affect drought or heat tolerance,” said Professor Bartlett. “These findings show these varieties could be more resilient to climate change than expected.”

The experts investigated how grapevines regulate their stomata­, tiny pores found on the surface of leaves. The functioning of these pores determines how much carbon dioxide is taken in for photosynthesis and how much water evaporates from the leaves. 

Grapevines must strike a balance between opening their stomata to take in CO2 for growth and ripening and closing the stomata to reduce evaporation and water stress.

Some of the desired fruit characteristics, such as the flavor of the grapes, are enhanced when the vines experience a small degree of water stress. However, too much water loss can prevent the grapes from achieving their desired flavors. 

The researchers examined traits for 34 grape varieties, and established the associations between grape varieties and regions. The study was focused on European regions, where irrigation is widely restricted, to gain a better understanding of the direct effects of changes in local climate.

The experts found that grape varieties grown in regions that experience more hot and dry conditions, such as the Sangiovese and Montepulciano varieties of Italy, kept their stomata closed more than varieties like Sauvignon Blanc from cooler, more humid regions. “This strategy would help these varieties save water,” said study co-author Gabriela Sinclair.

Professor Bartlett warned that these traits may have unintended consequences as heatwaves become more extreme. By restricting evaporation too much, the grapevines could allow their leaves to reach damaging temperatures, reducing their ability to photosynthesize and limiting the sugars available for ripening.

“We have more work to do to understand how these traits will affect grapevines as the climate reaches new extremes,” said Professor Bartlett. “These findings show that traits will be important to consider when we predict what will happen to different wine regions.”

The study is published in the Journal of Experimental Botany.

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By Chrissy Sexton, Earth.com Staff Writer