In uptake experiments from water cultures K+-influx in roots of sunflower (Helianthus annuus L.), cucumber (Cucumis sativus L.), birch (Betula verrucosa Ehrh.), lingonberry (Vaccinium vitis-idaea L.), and pine (Pinus silvestris L.) was related to the K+-contents of the roots. However, due to genotypic variation, no universal “optimum” K+-state of the roots for maximum K+-influx could be defined.
Ranking of Rb+ (K+-influxes into high K+ and low K+ roots of 11 cultivars of barley (Hordeum vulgare L.) brought the same sequence but the varietal differences were relatively greater in the high K+ roots.
Net K+ fluxes in barley roots were not related to K+-influxes due apparently to varietal differences in K+ effluxes from the roots.
Dry matter production per weight unit of K+ present in the plants (K+ use efficiency) was not related to the K+-influxes of the roots in the barley cultivars.
It is concluded that several both morphological and physiological plant parameters must be evaluated and combined before selecting varieties for efficient mineral nutrient exploitation is possible.