The relationship between N isotopic fractionation within soybean and N2 fixation during soybean development.
The contribution of N(2) fixation to overall soybean N uptake has most commonly been quantified by N isotope-based methods, which rely on isotopic differences in plant N between legumes and non-fixing reference plants. The choice of non-fixing reference plants is critical for the accuracy of isotope-based methods, and mismatched reference plants remain a potential source of error. Accurate estimates of soybean N(2) fixation also require information on N isotopic fractionation within soybean. On the basis of a previous observation of a close correlation between an expression of N fractionation within soybean and the proportion of plant N derived from atmosphere (%Ndfa) determined by (15) N natural abundance, this field study aimed at assessing the relationship between various expressions describing intraplant (15) N or N partitioning and %Ndfa during soybean development. Starting from a late vegetative stage until beginning senescence, the N content and N isotopic composition of shoots, roots and nodules of nodulated and non-nodulated soybeans was determined at eight different developmental stages. Regression analysis showed that %Ndfa most closely correlated with the difference in the N isotopic composition of shoot N minus that of root including nodule N, and that this relationship was similar to that obtained in a previous multi-site field study. We therefore consider this expression to hold promise as a means of quantifying %Ndfa independent of a reference plant, which would avoid some of the external sources of error introduced by the use of reference plants in determining %Ndfa.
Bio Forschung Austria, A-1220, Vienna, Austria.
Peter
P
Schweiger
Michaela
M
Hofer
Johann
J
Vollmann
Wolfgang
W
Wanek
D005591:Chemical Fractionation; D009584:Nitrogen / Q000378:metabolism*; D009586:Nitrogen Fixation; D009587:Nitrogen Isotopes / Q000032:analysis; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism; D018520:Plant Shoots / Q000254:growth & development / Q000378:metabolism; D053204:Root Nodules, Plant / Q000254:growth & development / Q000378:metabolism; D013025:Glycine max / Q000254:growth & development / Q000378:metabolism*
D009587:Nitrogen Isotopes; D009584:Nitrogen