Effects of some salts and sodicity on the growth of a Rhizobium leguminosarum bv. viceae strain isolated from a salt-affected soil

Abstract

The effects of sodium (Na+), calcium (Ca2+), magnesium (Mg2+), and boron (B) concentrations and sodicity, as measured by the sodium adsorption ratio (SAR), on the growth of a Rhizobium leguminosarum bv. viceae strain isolated from a salt-affected soil were studied. The rate of growth was measured in a yeast extract-mannitol broth, amended with salts having electrical conductivity (EC) of 4, 8, and 16 dS x m(-1). Each salinity level was prepared to achieve SAR values of 10, 20, and 30 with or without graded B concentrations of 0.5, 1, 3, and 5 mg x L(-1). We found that salinity levels equal to or more than 8 dS x m(-1) had negative effects on Rhizobium growth during the first days of incubation, but the effects became less pronounced after 1 week. Na+ concentrations of more than 1.1 g x L(-1) retarded growth, especially at high SAR values (i.e., at low Ca2+ concentrations). The retardation of growth increased with increases in EC up to 16 dS x m(-1), at all sodicity levels. Mg2+ added together with Na+ or with Ca2+ + Na+ affected growth more negatively than Ca2+ + Na+ alone. The effect of Mg2+ became more pronounced with increased salinities and sodicities. It was concluded that EC of more than 4 dS x m(-1) retarded growth of Rhizobium, but only at high sodicity levels. The relative specific ion effect on growth was in the order Na+ < Ca2+ < Mg2+. The harmful effect of Mg2+ on this strain was accentuated by adding Ca2+ to the cultural medium. When SAR increased from 10 to 30, Na+ had no clear effect on growth, irrespective of the accompanied cations, i.e, Ca2+, Mg2+, or Ca2+ + Mg2+. Growth was reduced by B concentrations as low as 0.5 mg x L(-1), and the B effect was enhanced by increased salinity.

Impact of Soil Salinization on Natural Vegetation and Land Deterioration

“…Moreover, salt accumulation could decrease plant growth and production indirectly through its impact on soil physical and chemical properties, such as soil structure, permeability, porosity, pH and nutrient availability. Also, salt accumulation has negative impact on biotic and biochemical properties of soil and soil microorganisms (17) and impeding the growth of rhizobia through osmotic stress or toxic effect of high concentration of ions (11), or reducing nodules formation, or reducing efficiency of formed nodules (10). High accumulation of salts can cause solid soil crust formation on the surface of the soil, which hinder seedling emergence.…”

أقلمة بعض المجتمعات النباتية الملحية والصحراوية بشرق الجماهيرية

“…) (Zonn and Kochubey, 1978;Selkhozprom Expor, 1980) Faituri et al, 19962001(Drought Nortcliff, 1988 Physiological Drought Mg +2 Page et al, 1982;Wild, 1995(Täckholm, 1974Jafri and El-Gadi, 1977;Boulous, 2002…”