Nitrogen mineralization and reorganization in casts of the geophagous tropical earthworm Pontoscolex corethrurus (Glossoscolecidae) |
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Authors: | P Lavelle G Melendez B Pashanasi R Schaefer |
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Institution: | (1) Laboratoire d'Ecologie des Sols Tropicaux, ORSTOM/Université P. et M. Curie, F-93 Bondy, France;(2) Estación experimental San Ramón, INIAA, Yurimaguas, Loreto, Perú |
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Abstract: | Summary Mineral N concentrations ranged from 133.1 to 167.8 g g-1 dry soil in fresh casts of the endogeic earthworm Pontoscolex corethrurus fed on an Amazonian Ultisol; this was approximately five times the concentration in non-ingested soil. Most of this N was in the form of NH
inf4
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. N also accumulated in microbial biomass, which increased from a control value of 10.5–11.3 to 67.5–74.1 g g-1 in fresh casts. During a 16-day incubation, part of the NH
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-N was nitrified and/or transferred to the microbial biomass. Total labile N (i.e., mineral+biomas N) decreased sharply at first (ca. 50% in the first 12 h), and then more slowly. The exact fate of this N (microbial metabolites, denitrification, or volatilization) is not known. After 16 days, the overall N content of the casts was still 28% higher than that of the control soil. Incubation of the soil before ingestion by the earthworms significantly increased the production of NH
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in casts. We calculate that in a humid tropical pasture, 50–100 kg mineral N may be produced annually in earthworm casts. Part of this N may be conserved in the compact structure of the cast where the cast is not in close contact with plant roots. |
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Keywords: | Earthworm Pontoscolex corethrurus Nitrogen mineralization Microbial biomass Casts Ultisol |
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