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Nitrogen mineralization and nitrification in terra firme forest and savanna soils on Ilha de Maracá, Roraima, Brazil

Published online by Cambridge University Press:  10 July 2009

R. H. Marrs
Affiliation:
NERC, Institute of Terrestrial Ecology, Monks Wood Experimental StationAbbots RiptonHuntingdon PE17 2LSEngland
J. Thompson
Affiliation:
Department of Biological ScienceUniversity of Stirling, Stirling FK9 4LA, Scotland
D. Scott
Affiliation:
Department of Biological ScienceUniversity of Stirling, Stirling FK9 4LA, Scotland
J. Proctor
Affiliation:
Department of Biological ScienceUniversity of Stirling, Stirling FK9 4LA, Scotland

Abstract

Soil mineralization and nitrification rates were measured in (1) undisturbed and felled gaps of varying size in terra firme forest, and (2) along a forest – savanna transect, on Ilha de Maracá in northern Brazil. Both rates were similar to those found in studies of other forests with a marked seasonal rainfall pattern. However, rates were much lower than those of tropical forests where there is little seasonality in rainfall. A major finding was that the highest rates were during the transition between dry and wet seasons, implying that wetting and drying may be an important initiator of soil nitrogen flux. Felling had little effect on either process up to a gap size of 2500 m2. In the forest-savanna study, nitrogen mineralization was lower in the savanna in all seasons, but in the wet season when the savanna soils were water-logged NH4+-N was immobilized. Experimental additions of nutrients identified two important results; first that added NH4+-N was quickly immobilized rather than nitrified – this may be an important nutrient conservation mechanism, and second that soil calcium appeared to be a limiting factor, either directly or through a pH effect.

Type
Research Article
Copyright
Copyright © Cambridge University Press 1991

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