Young Reproductive Structures Promote Nitrogen Fixation in Soya Bean

In many legumes the transition from the vegetative to the reproductivephase of development is associated with a marked increase inthe rate of symbiotic nitrogen fixation. In soya bean [Glycinemax (L.) Merr.), the removal of reproductive parts at differentstages of their development showed that the increase in nitrogenfixation rate was primarily due to the presence of flower buds.The increase in the fixation rate of intact reproductive plantswas accompanied by a rapid increase in the weight of noduleson lateral roots and it is suggested that these nodules areresponsible for much of the nitrogen fixation which occurs duringreproductive growth. Maintaining plants in the vegetative stateprovided evidence which suggests that it is the flower budsand not the flowering stimulus which are responsible for theincrease in fixation rate. The marked effects on vegetativegrowth of removing reproductive parts suggests that the mechanisminvolved in the promotion of nitrogen fixation may be hormonal. Glycine max (L.) Merr., soya bean, nitrogen fixation