Winegrowing under rising CO2 (Giesco minutes)
Minutes from the Giesco
The XXIth giesco conference took place in Mendoza between November 6 and November 10th, 2017. The 4 days meeting gathered international scientists to discuss advances in the field of viticulture. We would like to share some of the topics discussed during the 2017 edition. Today we summarize some of the talks focusing on rising CO2 effects on wine grape production.
Vine performance and rising atmospheric CO2
Vineyard performances are affected by rising temperatures but also by rising atmospheric CO2. CO2 measurements show an annual increase of 1.5 to 3 ppm and this will affect plant performances such as photosynthesis. But how?
Dr Wolfhart (Germany) discussed whether viticulture is sensitive to elevated CO2. To tackle this question, a project consisting of enriching atmospheric CO2 in open air was started 3 years ago in a german vineyard. The Free Air Carbon Enrichment (FACE) project studies yield and physiological performances for Cabernet sauvignon and Riesling.
FACE projects exist for various crops and consist of increasing atmospheric CO2 locally. Plants surrounded by CO2 emitters thrive in a richer CO2 environment. Those experiments are important to predict the impact of rising CO2 in tree stand (Figure 1) as well as vineyards (Figure 2)
Figure 1: FACE experiment in tree stand : Aerial view of the Oak Ridge experimental site (ORNL photo)
Figure 2 : FACE project in vineyard (photo from Winfried Schönbach, Hochschule Geisenheim University)
What do we expect from rising CO2 onto vine performance ?
Higher atmospheric CO2 is expected to increase yield and vigor. This reflects the fact that higher vine carbon intake is observed in response to higher CO2; which in turn leads to a yield gain and a leaf area gain. Thus, on a practical level, quantifying the effect of higher air CO2 is important topic to optimize leaf area and yield management in the near term. In the context of rising temperatures , rising CO2 and water shortage, winegrowers are faced with two questions:
1) Can higher CO2 levels compensate for the negative effect of high temperature on yield? In other words, could it be that yield losses caused by warmer temperatures – which favor berry dehydration before harvest-, be compensated by a yield gain resulting from higher CO2?
2) How are plant photosynthesis and water use responding to higher CO2? Since CO2 and water go across stomata in opposite directions, maybe less stomata aperture will be needed to assimilate the same amount of carbon….which would reduce vine transpiration hence vine water use?
What can we really predict from vine response to higher CO2?
In order to simulate realistically our atmosphere in the future, Dr Wolfahrt and her team have explored those questions while increasing atmospheric CO2 by 20% above ambient (400 ppm to 500 ppm) under field conditions. Their results show:
- · Lateral leaf area significantly increases
- · Contrarily to what was expected, an increase in sap flow is also observed! This means that higher CO2 levels in the atmosphere can increase water use!
- · Concentration in sugars decreases, but not significantly
- · Total acidity, berry weight and berry number per cluster increase. Consequently, yield increases significantly.
After 3 years, researchers anticipate that higher CO2 levels will increase significantly growth, vigor and yield by its impact on photosynthesis. However, resulting effect of higher CO2 on increasing vine water use are a surprise. Winegrowers and winemakers will need to anticipate how much vine water use is likely to increase to adjust viticultural practices as CO2 rises. On a side note, it is relevant to point that the impact of CO2 on wine production is also a concern for wine composition as noted by wine critics (https://winejournal.robertparker.com/rising-alcohol-in-wines-and-rising-co2-levels). As such, the impact of rising CO2 is a concern not only from a vineyard management standpoint. It should also affect wine consumers and the taste of future vintages.
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