Effect of Cations on the Growth of Fluorescent Pseudomonad Isolates from Spinach Roots Grown in Soils with Different Salinity Levels

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Effect of inorganic ion concentrations in culture solution on the growth of Pseudomonas putida and P. fluorescens isolates from spinach roots grown in soils with high-salinity(H-soil)and low-salinity(L-soil)levels was investigated. Both H- and L-soils were taken from the topsoil of a greenhouse for spinach cultivation and a nearby fallow field, respectively. In the H-soil inorganic ions had accumulated due to the high rates of application of fertilizer. Among the ions, the concentrations of Ca^<2+> NO_3^-, and SO_4^<2->in the H-soil were significantly higher than those in the L-soil. Among the inorganic ions tested (K^+, Na^+, Ca^<2+> Mg^<2-> Cl^-, NO_3^-, and SO_4^<2->), Ca^<2+> was found to be the most inhibitory on the growth of isolates. In addition, the isolates from the H-soil were more Ca^<2+>-tolerant than those from the L-soil. Consequently, the growth tolerance to Ca^<2+> stress of the total 80 isolates, 40 each from the H-soil and L-soil, was compared at 150 mM Ca^<2+>. Most isolates from the H-soil showed a significantly higher tolerance. The higher tolerance to Ca^<2+> of the isolates from the H-soil may have been acquired through selection under increasing Ca^<2+> stress in the field. The Ca^<2+> tolerance of the fluorescent pseudomonad strains may account for their survival and root-colonizing activity in soils with Ca^<2+> accumulation.
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