Date of Award
Doctor of Philosophy
Nitrogen (N) is present in proteins, enzymes, cell structures, purines and pyrimidines in DNA and RNA molecules, photosynthetic pigments, and several other types of molecules in all living organisms. Nonetheless, even though N makes up more than 78% of the atmosphere, it is reported to be the most frequent deficient nutrient in plants. Nitrate (NO3-) and ammonium (NH4+) are the N forms absorbed by plants from soil, but legume crops can establish symbiotic relationships with rhizobia bacteria, and fix N2 from the atmosphere. In soybean, increasing yield and protein content are raising the crop's N requirement; therefore, enhanced N2 fixation is seen as a reliable path to avoid the use of N fertilizers. In this study, the objective was to perform a comprehensive screening in greenhouse and field conditions of soybean genotypes for traits related to N2 fixation. The purpose was to identify among the soybean genotypes different N2 fixation profiles at early and late stages, as well as to investigate their capacity to accumulate above-ground N and supply carry-over N to following crops. The results showed different profiles among the soybean genotypes for early and late N2 fixation capacity, both in greenhouse and field evaluations. Different traits were correlated to either early or late N2 fixation activity. Soybean and winter-rye shoot dry mass were evaluated in the field to assess above-ground N accumulation and carry-over N, respectively. Soybean genotypes were identified with specific capacities to accumulate N in above-ground biomass or supply N to winter-rye. The patterns of N2 fixation identified in this study, as well as the different abilities to accumulate N above-ground or supply N to following crops, could assist in the selection of superior lines with improved N2 fixation capacity.
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