Ion Distribution Pattern in Various Alfalfa (Medicago sativa L.) Organs Respect to Phytomass under Saline Conditions

A greenhouse research work was conducted to study the patterns of Na+ and K+ distribution in root, stem and leaf during three growth stages of four Iranian alfalfa ecotypes and to find correlation between these patterns and plant salt tolerance. Treatments were replicated three times in a factorial experiment of a completely randomized block design. Based on the threshold of salt tolerance in alfalfa, three levels of salinity (control, 7 & 12 dS/m), were employed as salt stress treatments. The dry weight of roots, stems and leaves were determined and their Na+ and K+ concentrations measured. K+ concentration was reduced by increasing salinity, while Na+ concentration increased. The yield response of alfalfa ecotypes to the salinity treatments varied in various growth stages of the palnt. At seedling stage, Shirazi ecotype and during the second and third vegetative cuts, Hamedani ecotype showed the highest level of phytomass. The highest concentration of K+ in seedling stage was observed in Shirazi ecotype and in the second and third vegetative cuts, this was observed in Hamedani ecotype. When the concentration of Na+ in tissues exceeded the toxic threshold, the hazardous effects of this ion substantially influenced the ecotypes, yields. In both levels of salinity, concentrations of Na+ and K+ diminished strating from root towards shoot in the studied ecotypes. Therefore, Na+ concentration in root was more than those in stem and leaf under saline conditions, which could be attributed to the remobilization of Na+ from the shoot to the root. The lowest rates of Na+ in the studied plant parts at the second and third cuts, were also observed in leaves. The critical role of the leaves in photosynthesis and plant survival may have caused a prevention of Na+ entry into the leaves via various mechanisms. This however was associated with a considerable increase in the ion's concentration in shoot at the second and third cuts, as compared to root. So, regarding the importance of physiological processes in providing the salinity tolerance mechanisms, a study of other physiological characteristics which influence salt tolerance such as carbohydrates and nitrogen translocation from root to the shoot can have their special importance in future studies.