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Wednesday, June 20, 2012

Effect of Heat Wave on Grape Leaf Stomata

We are in for a heat wave in the Northeast and may be setting some record temperatures. I wondered what effect this will have on the grapevines. I learned in the UConn Master Gardener course that when the temperatures get too high, this adversely affects sugar accumulation. When I first heard that I was really puzzled. In order to understand this conundrum, I needed to learn about the functions of the grape leaf stomata. The image on the right shows the stomata which are located on the underside of the grape leaf.1 The stomata functions in the evaporation of water as well as in gas exchange. Carbon dioxide entering through the stomata is converted to carbohydrates via photosynthesis. When temperatures approach 100o F, the stomata on the leaves close in order to conserve water and the translocation of carbohydrates to the grapes stops. We may actually be okay because I believe that the grapes are currently in the lag phase of their growth. (See Vine Growth) However, if the grapes are in veraison, even 3-4 days of excessively high temperatures (>105o F) may retard ripening. Once temperatures have returned to normal, sugar accumulation can resume.2
1. Regents Biology Chapter 19
2. Nick Dokoozlian Grape Berry Browth and Development

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