WSET Diploma D1 Practice Exam

Potassium is central to how vines manage water status. It influences osmosis and stomatal behavior, which are the main levers controlling water movement and loss. Guard cells use potassium to open and close stomata, directly affecting transpiration and how much water leaves the plant. Potassium also supports cell turgor and the movement of water through the xylem and the distribution of sugars with water in the phloem, helping the vine balance uptake with demand, especially during fruit development. While nitrogen, phosphorus, and magnesium are essential for growth, energy transfer, and chlorophyll, they don’t regulate water flow as directly as potassium.