Abstract
The natural 15N abundance of amide‐exporting nodules was compared to that of shoots in 12 plant species. Nodules were statistically less abundant in 15N than shoots in one of three cultivars of Pisum sativum L., in Vicia faba L. and in Medicago sativa L., but the 15N depletion of nodules was very samall. Nodules were statistically more abundant in 15N than shoots in Trifolium pratense L., depending on time during the growing season, Cyamopsis tetragonaloba L. Taub. and 7 Lupinus species, but the enrichment was small except for C. tetragonalova and 6 Lupinus species. Nodules of 3 Lupinus species infected with Rhizobium lupini isolated from Lupinus subcarnosa Hook, were only slightly enriched in 15N, but nodules of two of these species were substantially enriched in 15N when infected with a mix of other Rhizobium lupini strains. The third species, L. texensis Hook., was not infected by this mix of strains. Differences in 15N abundance between nodules and other tissues of amide‐exporting and ureide‐exporting nodules from several studies are tabulated. All ureide‐exporting nodules in this tabulation are enriched in 15N. Amide‐exporting nodules are considerably more variable in this regard. These results confirm that events associated with ureide synthesis or transport cannot be the sole cause of the substantial 15N enrichment seen in nodules.
Published Version
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