Differential Responses in Potassium Absorption and Use Efficiencies in the Halophytes Catapodium rigidumand Hordeum maritimumto Various Potassium Concentrations in the Medium

AbstractThe changes in biomass production, root length, mineral nutrition, potassium absorption efficiency (KAE), and potassium use efficiency (KUE) of the halophytesCatapodium rigidumandHordeum maritimumin 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 Cédria (a Mediterranean coastal area) 30 km south-east of Tunis for four months from the autumn to winter of 2007–2008.H. maritimumbiomass production was not significantly affected by the K+concentration, butC. rigidumgrowth was increased significantly with increasing K+concentration in the medium. Root/shoot dry weight ratio remained constant inC. rigidum, but decreased significantly at 1000 and 3000µM K+inH. maritimum.KAE increased but KUE decreased significantly with increasing K+concentration in the medium in both species. However, KAE was higher inH. maritimumthan inC. rigidumshowing 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 ofH. maritimumto express its optimal growth can be attributed to its higher efficiency to acquire and transfer K+to shoots.