Root Nitrogen Remobilization and Ion Status of Two Alfalfa (Medicago sativa L.) Cultivars in Response to Salinity Stress

Abstract

In a pot experiment the responses of two alfalfa cultivars differing in salt tolerance were evaluated in terms of root nitrogen remobilization rates (RNRR) and their relationship with the ionic status of the plants. A split‐plot design with factorial treatments in three replications was used. Three levels of salinity stress with electrical conductivities (ECs) of 1.2, 7 and 12 ds m−1 were established in irrigation water by using tap water with and without NaCl. The average data taken from plant materials at three defoliations were used for statistical analysis. Each time, plant materials were harvested at the 10 % flowering stage and then 10 days later. From the results observed, it was found that alfalfa shoot growth is highly dependent on RNRR under salinity stress. However, the total N reserves within the roots do not appear to be a limiting factor. The high positive correlation coefficient between shoot K+/Na+ and RNRR (r = 0.77; P = 0.01) indicates that lower demands for N because of diminished metabolic activities within the shoot sink may have reduced the rates of root N utilization. Unlike in some other species, the shoot K+ concentration and contents of alfalfa plants were significantly reduced by increasing salt stress. However, a relatively suitable K+/Na+ ratio of 7.1 is maintained in the shoots at the second level of salinity, as lowering the rates of salt induced an increase in Na+ uptake (Na exclusion). The salt tolerance recognized in the Bami cultivar may be attributed to the 339 % increase in its selectivity rates of K+ over Na+ in ion transport from the soil to the shoots, as the shoot Na+ content did not increase with increasing salt levels.

Emergence, Forage Production, and Ion Relations of Alfalfa in Response to Saline Waters

“…According to this consideration, changes in the selectivity of K + are related with the decreasing shoot K + and decreasing K/Na ratio in the shoots when salinity increases. This decreasing K + with increasing salinity in alfalfa has also been reported in other studies (Ashraf et al, 1986; Grieve et al, 2004; Mohammadi et al, 2008; Rogers et al, 1998). Among the test cultivars, Salado was particularly efficient in maintaining the lowest shoot Na + concentrations, especially up to EC iw 18.4 dS m −1 and consequently the highest K/Na ratio among the cultivars.…”

The effect of salinity (NaCl) on germination and early seedling growth of Lathyrus sativus and Pisum sativum var. abyssinicum

“…abyssinicum, respectively) were from 5 dSm -salinity level, which were statistically different from the control. The present findings are in agreement with the results of other researchers on Alfalfa and Ryegrass (Mohammadi et al, 2008;Pessarakli and Kopec, 2009). …”

Performance of Some Alfalfa Cultivars under Salinity Stress Conditions

“…Studies performed on other species, under saline conditions, show that the growth inhibition is due to a nutrient uptake alteration (Sibole et al, 2003;Mohammadi et al, 2008) or to a toxic Na and Cl intra-cellular concentration occurring in the stressed plants (Sannazzaro et al, 2007). On the other hand, with increasing NaCl concentration (Figure 1), the proline content recorded in shoots of all varieties significantly increased as many researches have already reported (Petrusa & Winicov, 1997;Chelli-Chaabouni et al, 2010;Torabi & Halim, 2010).…”