If we believe Jacobsen and Pratt’s findings on plant cavitation (see the previous blog post), then logically vineyards would operate with 100% of vessels full of air most of the time! In other words, many vineyards would be dead!
To understand the reasoning, let’s take a look at the figure below in order to get the big picture.
The chart shows the average xylem water potential values using over 25 years of data obtained in Bordeaux (from Cheval Blanc) and various vineyards in California.
Figure 2: Average monthly water potential over multiple years. (Source: Sylvain Delzon’s presentation from Vintage Report Napa 2016)
We observe that between June and October (month 6 to 10), water potential average ranges between -15 and -20 bars. According to Jacobsen and Pratt, when water potential is more negative than -12 bars, more than 90% of vessels are full of air. Consequently between June and October, vineyards would be functioning with 100% of vessels full of air! In other words, vineyards would be dead. Because this does not make sense, something must be wrong with Jacobsen and Pratt’s results unless a mysterious vine specific mechanism keeps refilling vessels after cavitation.
Thus, two new questions arise:
- Is it possible that a measurement artifact existed when results were obtained in Jacobsen and Pratt’s study?
- Is it possible for a vine to refill its vessels during the season even if water pressure is negative?
Because of their economic impact on vineyard sustainability, those two questions have been under a lot of scientific scrutiny since 2012. The results will be really helpful to better assess vine water needs. The story continues and is still being written today. We will soon discuss the most recent findings on the vine cavitation controversy.
Stay tuned: more to come soon.
Since a moderate level of stress has been demonstrated to benefit fruit and wine quality, it is in the best interest of winemakers and vineyard managers to track plant susceptibility to cavitation. The goal is to maintain vineyard health while getting the benefit of a moderate water deficit. If you want to monitor water deficit and avoid cavitation in your vineyard, our product Sap Flow helps addressing that goal while saving significant amounts of water.