The effect of salt stress on the growth and sUl"lival of fou introduced
Sinorhizobium me/ifoti strains in the rhizosphere of alfalfa Medicago sativa L. was
studied. Response to inoculation with these strains and the competition among them
and against native rhizobia were investigated in two salt affected soils ith different
salt concentrations of 10 and 36 dS m", Results showed thai none of th introduced
rhizobial strains was affected by the soil salinity up 10 36 dS m' as they ere abte to
grow and survtve in the rhizosphere of alfalfa plants. However. nodule formation by
both native and introduced rhizobial slrains was negatively affe,ted by salt
concentration. This indicates thai the first step in nodule formation is extremely
sensitive to salinity. likely due 10 Ihe effect of salinity on the root infection sites but not
on the survival of rhizobia. Acetylene reduction of nodulated roots at'd nitrogen
accumulation were adversely affected by salt concentration in the soil. This may show
the negative effect of salt stress on plant growth and subsequently nod Ie function.
Patterns of rhizosphere COlonization by the introduced rhizobia! straims declined
markedly with increased salt concentration of the soil. Data show;d thai the'
introduced rhlzoblal strains could grow. survive and fix nitrogen at salt concentrations
inhibitory to the growth of alfalfa. Therefore, we recommend that the futur~ studies on .
the effect of salinity on symbiotic N2 fixation should focus more on aspects related to
the symbiosis rather than the study of each separate partner.