Differential Responses in Potassium Absorption and Use Efficiencies in the Halophytes Catapodium rigidum and Hordeum maritimum to Various Potassium Concentrations in the Medium

The changes in biomass production, root length, mineral nutrition, potassium absorption efficiency (KAE), and potassium use efficiency (KUE) of the halophytes Catapodium rigidum and Hordeum maritimum in response to potassium availability were assessed under natural conditions. Plants were cultivated in the greenhouse of the experimental station of the Biotechnology Centre of Borj Cedria (a Mediterranean coastal area) 30 km south-east of Tunis for four months from the autumn to winter of 2007-2008. H. maritimum biomass production was not significantly affected by the K(+) concentration, but C. rigidum growth was increased significantly with increasing K(+) concentration in the medium. Root/shoot dry weight ratio remained constant in C. rigidum, but decreased significantly at 1000 and 3000 mu M K(+) in H. maritimum. KAE increased but KUE decreased significantly with increasing K(+) concentration in the medium in both species. However, KAE was higher in H. maritimum than in C. rigidum showing a contrasting response to K(+) concentration between the two species. Overall, the maintenance of a cationic balance may be explained by cation antagonism. The lower K(+) requirement of H. maritimum to express its optimal growth can be attributed to its higher efficiency to acquire and transfer K(+) to shoots.