Accumulation of potassium in grapevine rootstocks (Vitis) as affected by dry matter partitioning, root traits and transpiration

Background and Aims: A high concentration of potassium (K) in grape juice can lead to high juice pH (e.g. > 3.8) and, in turn, wine of lower quality. The concentration of K in grapevine can be controlled by rootstocks. However, the differences between rootstocks in the accumulation of K in grapevines and mechanisms of regulation of K are not well known. The current study addresses these issues. Methods and Results: Rootstocks (on own-roots) Freedom, Schwarzmann, 1103 Paulsen, 110 Richter, 140 Ruggeri and 101-14 Millardet et de Grasset were grown in sand for 56 days in a glasshouse and watered daily with 3 mM K. At Day 56, rootstock 1103 Paulsen had the highest total K uptake, while 101-14 Millardet et de Grasset and 140 Ruggeri had the highest concentration of K in shoot and roots, respectively. Total K uptake in rootstocks was positively related to the dry weight of the whole grapevine, relative growth rate, total root length and total root surface area. Translocation efficiency of K in rootstocks was positively related to shoot : roots dry weight and shoot demand for K per unit root weight. Total K uptake and accumulation of K into the shoot were not affected by transpiration, but concentration of K in the shoot was positively related to the concentration of K in the xylem sap. Conclusions: The results show genetic differences between grapevine rootstocks in K uptake and transport, and highlight the importance of growth, dry matter partitioning, root traits and root pressure, and the lack of significance of transpiration, in the accumulation of K.