For all organisms, heat means a state of stress and thus also for plants like grapevine. Rising temperatures due to climate change lead to lower productivity of important crops. Heat upsets cell metabolism and impairs photosynthesis, which almost stops at over 40 °Celsius. Extreme heat can even be fatal for plants. That is why plants have developed a variety of reaction mechanisms. Just like humans, plants also try to protect themselves from heat by evaporation, which leads to relatively rapid cooling. This process, called transpiration, is controlled by the stomata (stomata ) of the leaves.
In combination with low humidity, dry wind and strong sunlight, however, this leads to additional water stress. With rising temperatures, respiration (supply of energy for growth) also increases strongly, during which the malic acid is decomposed. The result is wines that are low in colour and acidity and taste bland. The breeding of new heat-tolerant grape varieties is becoming increasingly important in the context of these developments. Foam cress (Arabidopsis) is often used to study the heat reactions of plants. The genome of this plant is comparatively simple and has already been completely decoded. See also under drought.
The glossary is a monumental achievement and one of the most important contributions to wine knowledge. Of all the encyclopaedias I use on the subject of wine, it is by far the most important. That was the case ten years ago and it hasn't changed since.Andreas Essl