Effects of rhizobial bacteria on K, Ca and Na concentration of wheat (Triticum aestivum L.) in saline soils

Soil salinity is one of the major agricultural problems and it is limiting crop productivity in many parts of the cultivated areas all over the world. Saline soils are differentiated by the presence of great ratios of Na/Ca، Na/K، Ca2+، Mg2+، and Cl/NO3 (Gratan & Catherine، 1993) and high levels of neutral salts in the surface layers، which are resulting from the capillary action (Al-Falih، 2002). Osmotic stress occurs when soluble salts increase in the soils and then results in specific ion toxicity (Agarwal & Ahmad، 2010). Therefore، one of the most important side effects of salinity is nutritional disorders. High concentration of NaCl in the root medium usually reduces nutrients uptake and affects the transportation of potassium and calcium ions in plant. (Gratan & Catherine، 1993) reported that the salinity of soils changes ionic strength of the substrate and it can influence mineral nutrient uptake and translocation. Salinity also changes the mineral nutrient availability and disrupts the mineral relations of plants. Hence، the main purpose of this research is to evaluate the effects of rhizobial bacteria inoculation on K، Ca and Na concentration of wheat (Triticum aestivum L.) in saline soils.

Soil sample was collected from Astan Ghodse Razavi farm، Mashhad Iran، and then was dried and passed through a 12-mesh (approximately 2 mm) screen. Soil sample was divided into three parts and then was placed into three containers. Each container was watered by a different proportion of saline water (EC= 10 dS. m-1). Salinity of soils was regularly monitored until three salinities (2، 6 and 10 dS. m-1) came out. Then، a completely randomized design with a factorial arrangement was carried out in a greenhouse condition. The experimental factors included four levels of inoculation (Sinorhizobium meliloti، Bradyrhizobium japonicum and Rhizobium leguminosarum and control) and three levels of soil salinity (2، 6 and 10 dS. m-1) with three replications. Wheat seeds were sterilized in 5% sodium hypochlorite for 2-3 minutes and were washed several times and then were germinated and seedlings were inoculated with bacterial strains. Inoculated wheat seedlings were grown in 1 kg pots. Wheat seedling was watered with sterilized water for one month and was harvested for chemical analysis. Potassium and sodium concentrations in plant tissues were determined by flame photometer and calcium concentration was measured by using Atomic absorption spectroscopy (AAS).

The results showed that the root and shoot dried weight، K and Ca concentrations and K/Na ratio in wheat shoot were significantly decreased with increasing soil salinity. The lowest shoot and root dry weight were observed in high level of salinity (10 dS. m-1). Inoculation of wheat seedlings with rhizobial bacteria had a positive effect on shoot and root dry weight. The highest shoot and root dry weight were obtained when wheat seedlings were inoculated with Sinorhizobium meliloti in non-saline soil treatment (2 dS. m-1). Calcium concentration increased significantly in all levels of salinity when wheat seedlings were inoculated with Rhizobium leguminosarum. Among all tested strains، Rhizobium leguminosarum had a prominent effect on growth of wheat seedlings. With increasing soil salinity، the concentration of sodium increased in shoot and root tissues and K/Na ratio declined dramatically. The lowest K/Na ratio was found in the highest level of salinity (10 dS. m-1). On contrast، the K/Na ratio in wheat shoot was amplified when wheat seedlings were inoculated with rhizobial strains. The highest K/Na ratio was observed in Rhizobium leguminosarum treatment. There are data that show that wheat cultivars having greater leaf K: Na، K ion flux، and growth improve under saline conditions (Mayak et al.، 2004; Morant Manceau et al.، 2004; Yao، 2010). It seems that Rhizobium leguminosarum reduced the detrimental effect of salinity to some extent. Acknowledgements: This research was partially supported by vice president for research and technology of Ferdowsi University of Mashhad. We thank our colleagues who provided insight and expertise that greatly assisted the research، although they may not agree with all of the interpretations or conclusions of this paper.