Nitrogen Partitioning During Early Development of Supernodulating Soybean (Glycine max [L.] Merrill) Mutants and their Wild-Type Parent

The relative importance of fixed N², cotyledonary N, and nitratefor growth of seedlings of soybean cv. Bragg and two of itsnitrate tolerant supernodulating (nts) mutants (intermediatents 1116 and extreme nts1007) was investigated during symbioticdevelopment in the presence of nitrate (3.0 mol m^–3) using¹⁵N techniques. Newly-fixed N₂ and nitrate were both major sourcesof N for nodule development and nitrate principally supportedearly shoot and root growth in Bragg. In the nts mutants, however,all plant parts and nodules in particular, relied more on Nstored in the cotyledons. This resulted in later nodule maturityand a period of prolonged N-starvation for the seedlings ofthe extreme supernodulator, and could be responsible for theirsubsequently lowered biomass accumulation compared to the parentcultivar. Key words: Nodules, N partitioning, supernodulating soybeans