In the previous blog post, we talked about past research efforts to understand plant cavitations. More recently, Jacobsen and Pratt obtained very surprising results on vine cavitations in 2012. According to the authors, with Grenache vines, every other xylem vessel is blocked by an air bubble once water potential reaches -3 bars. Cavitation gets even worse as water potential reaches more negative values. When water potential reaches -12 bars, every xylem vessel is blocked by an air bubble.
To understand why those results were so surprising and what could be their practical applications for vineyard sustainability and irrigation practices, let’s have a look at the figure below.
Source: Sylvain Delzon’s presentation at Vintage Report Napa 2016 reporting results published by Jacobsen and Pratt, 2012
As you can see if you go from right to left, water potential gradually reaches more and more negative values, which is what you expect as soil moisture availability gradually declines. The data in red suggest that vines have 50% of their vessels cavitating at – 3 bars and 90% of their vessels cavitating at -12 bars. The data in green show that stomata are fully open until water potential reaches – 5 bars. Stomata are gradually closing as water potential decreases between -5 bars and -15 bars. When water potential gets lower than -15 bars, stomata are fully closed.
If true, these results would have a tremendous impact for the wine industry. Indeed, vines would be much less tolerant to drought than we thought previously. Consequently, irrigation should be more frequent to prevent water potential from dropping to values lower than -3 bars and to maintain vineyard productivity. Thus, based on this study, Grenache, a varietal typically planted in arid climates where drought is often severe, would in fact always be cavitating.
As very few vineyards function between 0 and -3 bars, the take home from chapter 1 is that vines are always cavitating – if Jacobsen and Pratt’s results are true.
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 controversies to come soon.
Since a moderate level of water stress has been demonstrated to benefit fruit and wine quality, it is in the best interest of winemakers and vineyard managers to track plant water deficit variations. The goal is to maintain vineyard health while getting the benefit of a moderate water deficit. If you want to monitor water deficit, our product Sap Flow helps addressing that goal while saving significant amounts of water.