Abstract
Salinity stress causes various physiological dysfunctions in soybean (Glycine max (L.) Merr.). For example, reduced nitrogen (N) uptake due to salt-induced depression of nodule formation severely limits soybean growth and yield. Super-nodulating soybean genotypes were previously identified by their superior N2 fixation and photosynthesis. Here, we have tested our hypothesis that the super-nodulating En-b0-1 genotype is more salinity tolerant than a normal-nodulating genotype. The super-nodulating genotype and its parental normal-nodulating cultivar Enrei were grown in pots and subjected to saline conditions during the pre-flowering and reproductive growth stages. Under saline conditions imposed during pre-flowering, En-b0-1 formed heavier nodules, resulting in greater N uptake, higher photosynthetic activity, and greater biomass production compared with Enrei. Saline treatment increased the concentrations of sodium (Na) and chlorine (Cl) in all plant parts regardless of genotype; but in En-b0-1, the concentrations of these elements in shoots were significantly lower, while those in roots and nodules were higher than in Enrei. When the salinity treatment was imposed during the reproductive growth stages, En-b0-1 maintained higher N uptake, leading to better alleviation of salinity-induced yield reduction than in Enrei. The super-nodulating genotype En-b0-1 was more tolerant to salinity than its parental normal-nodulating cultivar, due to its superior nodulation and prevention of excessive accumulation of Na and Cl in shoots, which were retained in roots and nodules, thus supporting our hypothesis.
