Regardless of cause, data has proven today’s climate is indeed warming. The planet just had its hottest November on record, and 2020 may end up beating 2016 for the title of the warmest calendar year yet. While there are unnumerable consequences to a warmer climate, food and beverage concerns near the top of the list.
In a race against time, growers are working daily to either outsmart or adapt their crops to climate change expectations. Vintners are no exception, as grapevines are as sensitive to climate as consumers are to the taste of their wine.
While climate change is expected to make many grape-growing regions too hot and dry to produce high-quality wine from traditional varieties, scientists at the University of California, Davis have found a silver lining—wine grape varieties from regions that are more prone to stress have traits that could help them cope with climate change.
The study, published in the Journal of Experimental Botany, focused on how grapevines regulate their stomata, which are tiny pores on the surface of leaves that allow plants to take in carbon dioxide for photosynthesis and expel oxygen. Grapevines are constantly vying for balance when it comes to regulating the stomata—open it to take in the CO2 needed for growth and ripening or close it to reduce evaporation and water stress. A little water stress improves wine by concentrating the flavors and aromas in the grapes; but too much will prevent grapes from achieving their ideal balance of sugars, acids and tannins, creating flat, uninteresting wines.
In the study, lead author Megan Bartlett, a viticulture professor, and research technician Gabriela Sinclair, examined 34 grape varieties across Europe. They found that varieties grown in regions more likely to experience water stress, such as Italy’s Sangiovese and Montepulciano, kept their stomata closed more often than varieties like Sauvignon Blanc, which is grown in cooler, more humid regions. However, contrary to expectations, embolism resistance is impacted more by cool temperatures than dry conditions.
This led Bartlett and Sinclair to conclude that lower maximum stomatal conductance in warm climate grapevines could partly compensate for the effects of a greater evaporative demand. In this situation, the grapevines would maintain a high soil water availability longer over the growing season, but reduce maximum rates for photosynthesis.
“These stomatal traits could also compensate for the longer growing season in warm regions, by downregulating photosynthesis to extend the time to ripening into autumn,” the authors explain in their paper. “Conversely, cultivars in cooler regions could require greater gas exchange to gain sufficient carbon for ripening, since growing seasons are shorter and photosynthesis is potentially limited by cooler temperatures.”
Indeed, according to the study data, Tempranillo vines with higher photosynthetic rates accumulated sugar more rapidly. Meanwhile, Sauvignon Blanc exhibited a higher maximum stomatal conductance than the warmer-climate Syrah.
To adjust to a warmer climate, Bartlett and Sinclair suggest reducing transpiration through canopy management practices, as well as increasing the amount of water available to grapevines through deeper-rooting rootstocks and soil amendments. (Irrigation is restricted in European countries, so increasing water availability through those means is not currently an option.)
Even with these recommendations, the researchers say a water-saving stomal strategy is instrumental in the fight to improve grapevine resilience to climate change. While this study showed osmotic adjustment is a critical trait for vintners to leverage to produce the desired stomatal behavior, additional data is needed to identify more traits that will be crucial to resilience going forward.
“Experimental studies and modeling approaches that account for a wider range of physiology traits are needed to quantify the impacts of the stomatal traits on performance under different climatic conditions, including the future, hotter conditions projected for most wine regions,” Bartlett and Sinclair conclude.