Characteristics of Na+, K+ and free proline distribution in three xerophytes of Stipagrostis pennata, Calligonum polygonoides and Hammada salicornia, in Yazd province

Potassium, sodium and free proline play important roles in adaptation of plant species to arid conditions. Distribution of Na+, K+ and free proline in desert plants is not clear. In this study, the accumulation of Na+, K+ and free proline was investigated in three species namely, Stipagrostis pennata, Calligonum polygonoides and Hammada salicornia. These species are naturally distributed in Irano-Turanian region. Six plants were selected from each species in similar conditions, during dry summer of 2010. Soil humidity measurement showed that all plants were in drought conditions. Half of the plants were irrigated. The quantities of Na+, K+ and proline were determined in the roots and stems of all samples. Results showed that the concentrations of free proline in the stem and root of S. pennata were significantly higher than that of other two species and irrigated S. pennata. Furthermore, the concentration of K+ in the stem of H. salicornia was significantly higher than that of other two species and irrigated H. salicornia. Also, the concentration of K+ in the root of H. salicornia was higher than that of other species, but this concentration was not significantly different from the irrigated species. Sodium, like potassium content was higher in H. salicornia, but significant difference was not observed in its quantity between irrigated and unirrigated species. C. polygonoides after H. salicornia accumulated large quantities of Na+ in its stem. Sodium content was higher in the root of H. salicornia and C. polygonoides in comparison with S. pennata. Results also showed that K/Na ratio was less in roots of unirrigated species in all three species, particularly in S. pennata while it was high in stems of S. pennata H. salicornia compared to irrigated species. Consequently, it was concluded that the three species use different strategies to cope with drought.