Relationship Between Ion Accumulation and Plant Biomass of Alfalfa Under Salt Stress

Salinity is one of the major abiotic challenges influencing plant productivity worldwide. To examine the response of two alfalfa cultivars (Bami and Hamedani) to six levels of water salinity (0, 25, 50, 75, 100, 125 mM L-1 NaCl), a glasshouse experiment was conducted at the College of Agriculture, Shiraz University, Shiraz, Iran in 2008. The results showed that in Bami (which appeared to be more tolerant to salinity), with increasing salt stress from 7 to 125 mM L-1, dry weight per pot was significantly decreased from 15.1 to 10.3 g, while in Hamedani decrease in dry weight was started from 50 mM L-1 salinity level. In both Bami and Hamedani cultivars leaf area per pot was significantly decreased when salt stress was higher than 75 mM L-1. There was a significant difference in leaf relative water content (RWC) between the two alfalfa cultivars in 75, 100 and 125 mM L-1 NaCl salinity levels. With increase in salinity level, the Na+ concentration was increased from 220 to 565 mmol kg-1 dry weight in Bami, and from 238 to 643 mmol kg-1 dry weight in Hamedani. The Cl- concentration in Hamedani (622 mmol kg-1 dry weight in 125 mM L-1 NaCl) was higher than that in Bami (503 mmol kg-1 dry weight in 125 mM L-1 NaCl). The K+ concentration was increased from 203 to 604 mmol kg-1 dry weight in Bami, and from 135 to 571 mmol kg-1 dry weight in Hamedani. Furthermore, phytomass production in Bami was significantly correlated with K+ (r=0.97), and Ca2+ (r=0.96) concentrations, as well as with leaf area (r=0.50) and plant height (r=0.87). Path analysis showed that there were significant direct effects of leaf area (p=0.73), Ca2+ (p=1.02) and K+ (p=0.59) on dry weight in Bami. In Hamedani, there were significant direct effects of K+ (p=0.61) and Ca2+ (p=1.07 on dry weight. Overall, based on both correlation and path analyses, it was concluded that measurements of K+ and Ca2+ concentrations may be appropriate criteria for evaluating susceptibility of cultivars to salt stress. These results may also be used for screening the salt resistant cultivars of alfalfa.