Young Reproductive Structures Promote Nitrogen Fixation in Soya Bean

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Abstract
In many legumes the transition from the vegetative to the reproductive phase of development is associated with a marked increase in the rate of symbiotic nitrogen fixation. In soya bean [Glycine max (L.) Merr.), the removal of reproductive parts at different stages of their development showed that the increase in nitrogen fixation rate was primarily due to the presence of flower buds. The increase in the fixation rate of intact reproductive plants was accompanied by a rapid increase in the weight of nodules on lateral roots and it is suggested that these nodules are responsible for much of the nitrogen fixation which occurs during reproductive growth. Maintaining plants in the vegetative state provided evidence which suggests that it is the flower buds and not the flowering stimulus which are responsible for the increase in fixation rate. The marked effects on vegetative growth of removing reproductive parts suggests that the mechanism involved in the promotion of nitrogen fixation may be hormonal.