Nitrogen availability patterns in white-sand vegetations of Central Brazilian Amazon |
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Authors: | Sílvia Fernanda Mardegan Gabriela Bielefeld Nardoto Niro Higuchi Marcelo Zacharias Moreira Luiz Antonio Martinelli |
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Institution: | 1. Instituto Nacional de Pesquisas da Amaz?nia, Avenida André Araújo, 2936, 69060-001, zip code: 478, Manaus, AM, Brazil 2. Centro de Energia Nuclear na Agricultura, Universidade de S?o Paulo, Avenida Centenário, 303, Piracicaba, SP, 13416-000, Brazil
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Abstract: | Addressing spatial variability in nitrogen (N) availability in the Central Brazilian Amazon, we hypothesized that N availability
varies among white-sand vegetation types (campina and campinarana) and lowland tropical forests (dense terra-firme forests) in the Central Brazilian Amazon, under the same climate conditions.
Accordingly, we measured soil and foliar N concentration and N isotope ratios (δ15N) throughout the campina-campinarana transect and compared to published dense terra-firme forest results. There were no differences between white-sand vegetation
types in regard to soil N concentration, C:N ratio and δ15N across the transect. Both white-sand vegetation types showed very low foliar N concentrations and elevated foliar C:N ratios,
and no significant difference between site types was observed. Foliar δ15N was depleted, varying from −9.6 to 1.6‰ in the white-sand vegetations. The legume Aldina heterophylla had the highest average δ15N values (−1.5‰) as well as the highest foliar N concentration (2.1%) while the non-legume species had more depleted δ15N values and the average foliar N concentrations varied from 0.9 to 1.5% among them. Despite the high variation in foliar
δ15N among plants, a significant and gradual 15N-enrichment in foliar isotopic signatures throughout the campina–campinarana transect was observed. Individual plants growing in the campinarana were significantly enriched in 15N compared to those in campina. In the white-sand N-limited ecosystems, the differentiation of N use seems to be a major cause of variations observed in
foliar δ15N values throughout the campina–campinarana transect. |
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Keywords: | Nitrogen stable isotopes Nitrogen availability White-sand vegetation Campina Campinarana |
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