Effect of NaCl on the growth and the ionic balance K+/Na+ of two populations of Lotus creticus (L.) (Papilionaceae)

AbstractLotus creticus (L.) is a major pastoral and forage legume in the arid climate of Tunisia where salinity is a serious production problem. A laboratory experiment was carried out to assess the physiological behaviour of two populations of L. creticus (Msarref (Msf) and Oued Dkouk (Odk)) in a solid substratum in the presence of salt. The tested concentrations vary from 0 to 400 mM NaCl. It has been shown that the two populations of L. creticus are fairly tolerant to salt at growth phase. The growth productions are recorded in absence of salt, mainly at the population of Oued Dkouk. The presence of salt in the medium affects growth of the whole plant for both populations. Compared to root biomass, the aerial one was more affected by salt. For all treatments, plants of both populations remain able to produce and to allocate dry matter to the different organs. However, the salinity generated a disruption at the level of water feeding of plants of the two populations. Compared to root organ, water contents in aerial organ proved to be the least affected by salt. The survey of the relation of water content of leaves according to its production in biomass showed that the expression of growth potentialities is associated with a better leaves hydration until 100 mM of salinity. It seems then that the decrease of growth under saline stress is not associated to a water (osmotic) effect. The survey of the Na+/K+ ratio showed for both populations an increase of Na+ contents in aerial and root organs, with an excess of accumulation of these ions in the aerial organ particularly more marked at the population of Msarref. In spite of the predominance of the Na+ ions, the two populations, mainly Oued Dkouk, remain able to assure K+ selectivity. This selectivity is ensured mainly at the level of roots where high potassium content is recorded compared to the aerial organ. The tolerance of the two populations is probably acquired by their better faculty to assure K+ selectivity and to compartmentalize Na+ ions in leaves. Such a mechanism reflects probably an inclusive behaviour towards salt. This behaviour justifies the faculty of plants to maintain their growth even in very hard salinity conditions