ELEMENTAL COMPOSITION OF MEDICAGO-SATIVA UNDER SALINE CONDITIONS - RELATION TO BIOLOGICAL NITROGEN-FIXATION

The salinity tolerance of a Rhizobium meliloti strain, used as inoculum, was established by growing the strain for seven consecutive generations in a broth containing 0 - 1.2 % NaCl. Identical generation times and viable cell numbers were observed. Furthermore, the nodulation, plant yield and elemental composition of M. sativa grown on agar slopes responded identically to all inocula, irrespective of the levels of NaCl with which they were grown. The effect,of salinity on the ability of M. sativa to grow and fix nitrogen was tested on apr slopes containing 0 - 1.2 % NaCl. At 0.0, 0.2 and 0.4 % NaCl the induced fixation was identical as indicated by the constant values of nodulation and plant yield. However, a significant reduction at 0.8 and almost a total suppression at 1.2 % NaCl occurred. Commensurate was the effect of inoculation on the elemental composition of M. sativa as a function of salinity at the apr medium. The concentration of Mo, Mn, Sr, Cu and Zn, is clearly affected by fixation while salinity has no effect. Their concentration in the inoculated plants is significantly lower compared to the uninoculated at 0 - 0.4 % NaCl levels, when significant fixation occurred. In contrast, at 0.8 and 1.2 % NaCl their concentration in inoculated and uninoculated plants tends to overlap. On the other hand, the concentration of K, Rb, Br and Cl is affected mainly by salinity. Finally, Ni is affected by neither salinity nor nitrogen fixation.