Aerial root nodules in the tropical legume,Pentaclethra macroloba |
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Authors: | Cynthia A. Walter Amos Bien |
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Affiliation: | (1) Department of Biology, University of Chicago, 60637 Chicago, IL, USA;(2) Department of Ecology and Evolution, State University of New York at Stony Brook, 11794 Stony Brook, NY, USA;(3) Present address: Department of Biology, St. Vincent College, 15650 Latrobe, PA, USA;(4) Present address: Rara Avis, Apartado 8105, 1000 San Jose, Costa Rica |
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Abstract: | Summary Symbiotic nitrogen fixation in angiosperms normally occurs in buried root nodules and is severely inhibited in flooded soils. A few plant species, however, respond to flooding by forming nodules on stems, or, in one case, submerged roots with aerenchyma. We report here the novel occurrence of aerial rhizobial nodules attached to adventitious roots of the legume,Pentaclethra macroloba, in a lowland tropical rainforest swamp in Costa Rica. Swamp sapdings (1–10 cm diameter) support an average 12 g nodules dry weight per plant on roots 2–300 cm above water, and nodules remain in aerial positions at least 6 months. Collections from four swamp plants maintained linear activity rates (3–14 moles C2H4/g nodule dry weight/hr) throughout incubations for 6 and 13 hrs; excised nodule activity in most legumes declines after 1–2 hrs. Preliminary study of the anatomy and physiology suggest aerial nodules possess unusual features associated with tolerance to swamp conditions. High host tree abundance and nodulation in the swamp compared to upland sites indicate the aerial root symbiosis may contribute more fixed nitrogen to the local ecosystem than the more typical buried root symbiosis. |
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Keywords: | N fixation Legume-Rhizobium symbiosis Aerial nodules Pentaclethra macroloba |
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