There is an active controversy surrounding the frequency of cavitation with vines. In the last three blog posts, we talked about recent studies to understand vine cavitation. While chapter 2 implies that cavitation may happen all the time in vineyards, chapter 3 suggests that something does not fit with this view.
Interestingly, new technologies have been providing new answers to clarify the debate. Recently, scientists have learnt to rely on the X-ray and the synchrotron method to unravel how water is traveling through the plant. Despite its cost and disadvantage of being destructive, the synchrotron method is really interesting because it is capable of providing real-time views of plant cavitation.
A new view of plant cavitation
Take a look at the two stem sections of an oak tree below. They are obtained by new synchrotron-based Micro CT scan technology.
Stem sections of oak tree at -10 and -60 bars (Source: Sylvain Delzon’s presentation from Vintage Report Napa 2016)
In the left picture, almost all plant vessels remains functional (i.e. full of water) at the pressure of -10 bars. In the right picture, as expected in a situation of drought, water pressure goes down to -60 bars. We can see the presence of many air bubbles (the black dots) inside the vessels. The synchrotron technology reveals where cavitation happens and how widespread it is.
The synchrotron technology is currently used to understand vine resistance to cavitation.
A new view of vine cavitation
What about vines? Brodersen’s and his colleagues (2013) focusing on vines and using synchrotron illustrated what embolism looks like at different water pressure levels from -17 to -40 bars (see below). Authors observed that embolism spreads from inside out through connected vessels.
Representative patterns of embolism spread in grapevines from Brodersen et al (2013). Stem water potential values for A, B, C and D are -17, -21, -19 and -40 bars respectively.
The figure above demonstrates that severe levels of cavitation are not common at typical water potential values observed during the season (ie.generally >-20 bars, as seen in previous blog post – chapter 3).
Using synchrotron Delzon’s team findings also showed that cavitation only happens when water stress is very severe. In fact, cavitation occurs only after transpiration has stopped. In addition, Delzon’s team also observed that vines have the unique capability of recovering from cavitations by refilling their vessels. However, the vessels refilling may only happen under certain environmental conditions. The good news from this observation is that vines are capable of regrowing the next year after having experienced cavitation (unlike other trees). The not so good news is that during the season, those results challenge the view that irrigation can be efficient at refilling the vessels during the season. But this is another controversial story we will discuss later.
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.