Abstract
The influence of three potassium:rubidium (K:Rb) ratios (6:0, 5:1, and 4:2) on the xylematic transport of solutes in cucumber plants cv. Medusa supplied with both nitrate (NO3 ‐) (60%) and ammonium (NH4 +) (40%) was studied in greenhouse conditions. In the xylem sap of plants grown with a K:Rb ratio of 4:2, there was an increase in the transport of NO3 ‐, phosphate (H2PO4 ‐), calcium (Ca2+), magnesium (Mg2+), sodium (Na+), manganese (Mn) and boron (B) while that of organic‐N, organic‐P, K+, zinc (Zn), organic acids, and carbohydrates decreased, if compared with the sap of the plants supplied with K alone. The translocation of NO3 ‐, H2PO4 ‐, Ca2+, Mg2+, and Mn was enhanced and that of K+ and organic acids decreased when the plants were supplied with a K:Rb ratio of 5:1. The K:Rb ratio detected in the xylem sap was the same K:Rb ratio as in the solutions. However, in the cucumber plant substituting 33% of total K by Rb resulted in an alteration in the transport of solutes, probably due to a competition between Rb and K rather than between the latter two and NH4 +.