Makie Kokubun, Tohoku University, Sendai, Japan and Yukiko Yasuta, Graduate School of Agricultural Science, Tohoku University, Sendai, Japan
Salinity causes various physiological dysfunctions of soybean (Glycine max L.); the reduction in nitrogen (N) uptake due to salt-induced depression of nodule formation is a major process limiting its growth and yield. Super-nodulating soybean genotypes were previously characterized by superior N2 fixation and photosynthesis. We attempted to verify a hypothesis that super-nodulating genotype is more tolerant to salinity than normally nogulating genotype. A super-nodulating genotype En-b0-1 and its ancestral normally nodulating cultivar Enrei were grown its pots, and subjected to saline conditions during a pre-flowering stage and a reproductive growth stage. Under saline conditions during a pre-flowering period, En-b0-1, compared to Enrei, formed heavier nodule weight, resulting in a larger amount of N uptake, higher photosynthetic activity and greater biomass production. The saline treatment increased the concentrations of Na and Cl in all the plant parts regardless of genotype; but in En-b0-1, their concentrations in shoots were significantly lower, while those of root+nodules were higher than in Enrei. When the saline treatment was imposed during a reproductive grown stage, En-b0-1 maintained its N uptake higher, leading to an alleviation of salinity-affected yield reduction than Enrei. Thus our hypothesis was verified; the supernodulating genotype En-b0-1, compared to its parental normally nodulating cultivar, was more tolerant to salinity, due to its capacity of superior nodulation as well as the prevention of an excessive accumulation of Na and Cl in shoot, while withholding them in root+nodules.