ISSN:
1573-5036
Keywords:
Alnus incana
;
Betula papyrifera
;
N-fixation
;
isotope dilution
;
15N
;
reference plant
Source:
Springer Online Journal Archives 1860-2000
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Notes:
Abstract Seedlings ofAlnus incana (nodulated and non-nodulated) andBetula papyrifera were fertilized with varying amounts (0, 10, 25, 50, 100, 250 and 500 μg N g−1 soil) of labelled ammonium-N or nitrate-N (∼ 5.2 A% excess15N as ammonium sulphate or potassium nitrate). After 4 months in the greenhouse,15N excess in the plants were determined and an isotope dilution equation was applied to determine the percent of biomass N fixed by theA. incana/Frankia system. When ammonium was used as the sole N source and birch as the non-fixing reference, N-fixation accounted for 95%, 87% and 60% of the plant nitrogen yields with 10, 25 and 50 μg N g−1 rates, additions respectively. At the 100 μg N g−1 fertilization and above N-fixation accounted for less than 10% of the N yield. Similar results were obtained when non-nodulatedA. incana was used as non-fixing reference. With nitrate as the sole N source, N-fixation accounted for 98%, 97%, 97%, 86%, 56% and 12% of N yield with 10, 25, 50, 100, 250 and 500 μg N g−1 additions respectively. These values were similar for both types of reference plants. The direct isotope dilution method was compared to that of the total nitrogen difference method. There was good agreement between the two methods up to 50 μg N g−1 for ammonium and up to 100 μg N g−1 for nitrate. The difference method produced negative values at high concentrations of nitrogen fertilization. Again similar results were obtained by the two reference plants. The results indicate that birch can be used as a non-fixing control in isotope dilution studies but that care must be exercised in selecting the type and quantity of labelled nitrogen fertilizer.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF02232789
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