Little Spheres — What’s Going on with Wine Grapes?
Impacts of Climate Change on Wine Grapes
By: Claudia Althoen
Edited by: Katherine Hill, Katie Kelly
Wine grapes can’t drink their way out of climate change. In a Nov. 2016 paper published in the Journal of the Science of Food and Agriculture, researchers Leibar et al., researched the effects that conditions in a 2100 world impacted by climate change could have on grape yield. Before going into the specifics of the study, let’s peel back the skin of these grapes and learn the basics of wine grapes.
Grapes are well-adapted for where they’re grown and this makes them quite sensitive to climatic changes. According to Leeuwen et. al., it is nigh impossible to produce high-quality wines in subtropical or tropical locations due to the combination of excessive humidity and precipitation. However, there is also the problem of winter and spring frosts, and there can sometimes be a loss in bud fertility if temperatures are too low. Nevertheless, wine grapes are most successfully grown between 30 and 50-degree latitude south and north of the equator. This explains why some of the top exporters of wine are France, Italy, Spain, Chile, Australia, the United States, Germany, New Zealand, and so on. Grape growers know only too well the struggle of growing healthy grapes.
For grape growers, too much rain may ruin a significant portion of their crop. The fungus Botrytis cinerea causes the disease Grey Mold on grapes. The fungus loves humid conditions, and so growing grapes in such conditions would be considered a risk. The fungus appears and infests plants such as wine grapes during periods of excessive humidity. As a result, crop yields are lower, and the grapes usually oxidize more quickly, leading to a loss of aroma and can cause the wine to taste nutty. However, there is a flipside to this fungus.
In distinct white grape wine varieties, Botrytis cinerea is actually beneficial. In these cases, it is called ‘Noble Rot.’ Noble Rot is a rare occurrence, but when the right conditions do occur, the grapes can take on a sweeter form. The fungus enters through the skin of the grapes and steals water from the grapes. The result is overall less acidic grapes. How else are grapes altered by environmental conditions? As mentioned earlier, temperature plays a significant role in grape maturation.
Wine grapes are driven by temperature . Bud breaking, flowering, and ripening — or véraison, the French word for ‘onset of ripening’ or change in grape color — are all temperature dependent. Therefore, the higher the temperature, the more quickly grapevine phenology occurs. Phenology refers to the study of growth stages that recur in accordance to the temperature, day length, etc., related to specific seasons. Climate change is resulting in the extension of specific seasonal characteristics, such as higher temperatures and drier conditions, therefore resulting in expedited growth for grapes. As a result of a thinner ozone layer, there has been more surface radiation present. Radiation plays a role in wine grape production by increasing anthocyanin in grape skin. Too much radiation can result in a sunburn on the grapes, and could result in atypical aging. Also, a higher latitude results in higher exposure to radiation, meaning that vineyards at higher latitudes are more impacted. Anthocyanin are water-soluble pigments that turn blue, purple, or red depending on the pH of the plant. Anthocyanin has some health benefits, such as improving blood circulation and vision and treating hypertension and liver disease. The wine style produced (red or white), depends on how much and how frequently the grapevines takes in water. Red grape varieties generally need less water compared to the white variety types. Root length for grapevines varies depending on the availability of water, and so if there is more water available less root growth may be needed. However, since no system is perfect, there are losses when it comes to water retention.
Evapotranspiration, a measurement that can be used to determine soil water loss to the atmosphere, is the combination of the loss of water from the ground surface and the loss of water from the plant leaves, or transpiration. This measurement can be used to determine an irrigation schedule for grapes by knowing how much water the grapevine uses. Knowing specific tools used for grape production is useful in understanding the overall picture of grape yields and climate change.
Now that we have a basic understanding of wine grapes, let’s explore the impacts, both positive and negative, of climate change on wine grape crops. Climate change results in higher global temperatures overall, and for wine grapes, this means lower acidity. What are some of the other impacts?
On Nov. 14, 2016, a new study was published in the Journal of the Science of Food and Agriculture. In this study, Leibar and his team examined what would be an average grape yield and quality in the year 2100. For their simulation, they used Vitis vinifera, also known as the common grape vine. Rooting of the grape vine was induced using indole butyric acid, and a month later, they were all put into 2-L plastic pots that contained a mixture of perlite, peat, and vermiculite.
The grapes were put into two different growth chambers to determine the changes in grape yield, growth, and overall grape characteristics. One chamber contained CO2 resembling the emission levels we find today, along with current temperature, relative humidity (RH) conditions. RH refers to the ratio of how much water vapor is present in the air compared to how much could be in the air at a specific temperature. The second chamber was fitted with conditions that were predicted using a climatic simulation model. Based on the model predictions for the year 2100, the researchers used 700 umol CO2 mol-1, which is originally measured in ppm, but is then converted to micromolars. According to NOAA, each unit of umol mol-1 is equal to 10–6 mol CO2 per mol of dry air. In the study, the climatic model also predicted 4-degree Celsius increase in temperature, and a reduced humidity level.
The researchers also varied water and soil conditions. The plants were either well-irrigated or water-deficit. For soil, three different soil textures were tested (8, 19, or 41% clay). Overall, they tested grapes by altering glasshouse conditions, water availability, and soil textures.
Photo credit: http://onlinelibrary.wiley.com/doi/10.1002/jsfa.8086/full
In the figure on the left, volume of malic acid for each grape vine was measured against each soil texture. Malic acid is one of the primary acids present in wine grapes. It’s also found in other berries and fruits as slightly different type. Excessive malic acid, for example, can result in a sour-tasting grape. However, tartaric acid also plays a significant role in grape acidity, and so both acids are often measured. The figure shows us that acidity of the grapes decreased in the water deficit group, except for the 41% clay. A reason for lowered acidity for two of the three groups may be because of the cluster thermal effect, which is often caused by reduced vegetative growth.
In the study, the grapes were harvested when they all had the same sugar content. They found that the simulated conditions for 2100 resulted in shortened time between “fruit set and veraison and between fruit set and maturity” by seven to ten days. Fruit set occurs when the flower produces a berry. This shortened time may be a result of more arid conditions, which tends to be favorable for grapes. Leaf area and dry weight had been reduced for plants in the WD group and decreased the ability of the vine to root. They also found that soil texture affected root growth, but not grapevine growth. Rooting is crucial for wine grape vines since their roots can spread horizontally for some distance, but not grow very deep vertically. This may be important to consider for growers to adjust to future conditions.
FCC (forced climate change) reduced color intensity and anthocyanin concentration. However, soil texture didn’t necessarily affect growth since it’s possible that the amount of water available could have impacted the roots instead. The researchers did find that with greater macroporosity (allows for flow and transport of solutes) of the soil, such as sand, there was more root growth. Their results show that it’ll be difficult — and it is currently — to obtain a precise acidity desired, and it will only become more complicated to do so as climate change increases the extremes. Grape growers will have to plan and adapt to future conditions by considering all factors in grape growing, such as soil type, water availability, radiation. As climate change progresses, it may become more expensive and difficult to produce certain wine varieties, resulting in reduced yields.
References
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Leibar, U.; Pascual, I.; Morales, F.; Aizpurua, A.; Unamunzaga, O. Journal of the Science of Food and Agriculture 2016.
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*(link to the Leeuwen paper) https://www.cambridge.org/core/services/aop-cambridge-core/content/view/...
*(link to the Leibar paper) http://onlinelibrary.wiley.com/doi/10.1002/jsfa.8086/full
