Little Spheres — What’s Going on With Wine Grapes?

Effects of Climate Change 1.11

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, so either side of the areas impacted by Hadley Cells, which form between 30 degrees north and 30 degrees south. 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.

As shown in the image, Hadley Cells form between 30 degrees north and 30 degrees south. The combination of excessive humidity and precipitation are usually limitations of grape growing in these regions. Photo credit:

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.

Grey mold. Photo credit:

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.

Noble rot. Photo credit:

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. Radiation, of which climate change is impacting, plays a part in wine grape production by increasing anthocyanin in grape skin, which 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 outcome for grapes depends on how much and how frequently the grapevines takes in water since root length for grapevines will vary depending on the availability of water. There may be an intake of water, but since no system is perfect, there are losses.

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?

Bud breaking. Photo credit:

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. As we all know, 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 (volcanic glass), 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. For water, the plant received WD or WI (water deficit or well-irrigated). 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:

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.)

The figure shows us that acidity of the grapes decreased in the water deficit group, except for the 41% clay.

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. Leaf area and dry weight had been reduced for plants in the WD group and decreased the ability of the vine to root. Rooting is crucial for wine grape vines, and so 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, changing our world.

Thanks for reading my double-length post,

Claudia A.


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(link to the Leeuwen paper)

(link to the Leibar paper)

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