Response of Soybean to Salinity::III. Water Status and Accumulation of Mineral Ions

Our previous studies indicated that soybean genotypes displayed wide genotypic variations in their salt tolerance. The present experiment was initiated to analyze the pattern of changes in accumulation of different mineral ions and water relation traits associated with salinity in two soybean genotypes, differing considerably in their relative salt tolerance. AGS 313 (salt-tolerant) and Shohag (moderately susceptible) were grown in pots filled with soil and treated with 0, 50 and 100 mM NaCl solutions till maturity. Grain yield and yield associated characters, accumulation of mineral ions, such as Na + , K + and Ca 2+ in different plant parts and water relation traits, such as relative water content (RWC), water retention capacity (WRC), leaf water potential and exudation rate (ER) at 15, 30, 45, 60 days after treatment imposition and at harvest were measured. NaCl salinity affected markedly the grain yield and yield associated characters of the two soybean genotypes. However, Shohag was more affected by the salinity than AGS 313. The grain yield of the genotype AGS 313 was 56% and 32 %, whereas that of Shohag was only 22% and 13% at 50 mM and 100 mM NaCl, respectively. The grain yield reduction by salinity was attributed to the reduction in the number of pods per plant, number of seeds per pod and 100-grain weight. However, the number of pods per plant was most affected compared to the other characters. Salinity increased the content of Na + while it decreased that of K + and Ca 2+ in all the plant parts. The increase in Na + content and decrease in the accumulation of the other mineral ions due to salinity became larger with the plant age. Except for roots, Na + accumulation in different plant parts of Shohag was much higher than that of AGS 313 in all the measurements. However, K + and Ca 2+ accumulation in different plant parts of AGS 313 was substantially higher than that in Shohag. Moreover, under saline conditions, in AGS 313, the values of RWC, WRC, leaf water potential and ER were higher at all the levels of salinity and plant age than Shohag. It was concluded that the relatively high salt tolerance of AGS 313 was associated with the limited accumulation of sodium and high accumulation of different mineral ions in different plant parts, as well as the maintenance of better water relations under salinity than in the case of Shohag.