Potassium (K) is the principal mineral solute contributing to osmotic adjustment (OA) in many crop species, and the magnitude of OA under drought stress may be increased by application of K fertilisers. Genotypic differences in either the capacity for OA under drought stress or the efficiency of K uptake and utilisation by wheat have been separately documented. However, it is not known whether genotypic differences in K uptake and utilisation are linked to differences in OA under drought stress. In this study, we quantified changes in OA in response to variable K fertilisation among five wheat genotypes with contrasting efficiency of K uptake and utilisation. Fertilisation with K increased OA for most genotypes by increasing K+ uptake and translocation into shoots and its subsequent accumulation in young leaves when drought stress was imposed. Accumulation of K+ in young leaves accounted for 36-51% of OA among the genotypes. The magnitude of OA achieved by genotypes under K fertilisation was highly correlated with the net content of K accumulated in shoots. With K fertilisation, differences in shoot K+ content accounted for 84% of the difference in OA among wheat genotypes. By comparison, for plants without K fertilisation, K+ accumulation in young leaves contributed only 17-28% of OA. At low K supply, the magnitude of OA achieved by genotypes was independent of the content or concentration of K+ in shoots. Under K-fertilised conditions, genotype Nyabing achieved the highest OA under drought stress, accumulated the highest concentration of K+ in young leaves (-0.87 MPa, accounting for 51% of OA), and had the greatest net K+ content in shoots. Genotype Wyalkatchem accumulated the smallest content of K+ in shoots and the lowest K+ concentration in young leaves (-0.40 MPa, accounting for 38% of OA), and achieved the lowest OA under drought stress. The greatest OA was achieved where high genotypic capacity to take up K was paired with conditions of high soil K availability.
