Isotopic composition of plant and soil nitrogen on a precipitation gradient in the Brazilian Amazon Forest
Gabriela
Bielefeld
Nardoto, CENA/USP, gbnardot@carpa.ciagri.usp.br
Jean
Pierre
Ometto, CENA/USP, jpometto@cena.usp.br
(Presenting)
James
Ehleringer, University of Utah, jim@biology.utah.edu
Luiz
Antonio
Martinelli, CENA/USP, martinelli@cena.usp.br
Soil and foliar 15N-natural abundance and N concentration were evaluated in three terra-firme forests over Oxisols with annual rainfall ranging from 1950 mm to 3300 mm along the Brazilian Amazon Basin. The studied sites are located at FLONA-Tapajós (Santarém, PA - 2,85 S; 54,95 W), ZF-2 Reserve (Manaus, AM - 2,50 S; 60,0 W) and National Park of Pico da Neblina (São Gabriel da Cachoeira, AM - 0,48 N; 66,50 W). Regardless the site, a large increase in delta15N values was observed in the first 50 cm deep of soil. There was a significant positive correlation between foliar delta15N and N concentration. Soil and foliar delta15N values systematically decreased with increasing mean annual precipitation. The pattern of higher soil and foliar N concentration in the drier site (Santarém), together with the progressively enriched delta15N signature in vegetation, suggest that nitrogen cycling is more open at the drier site where an increasing fraction of ecosystem N losses should be probably 15N-depleted forms (NO3, N2O and NO). Ecosystems under higher precipitation regime appear to be more efficient in the recycling and conserving of mineral N. The difference between delta15N(foliar) and delta15N(soil) increased with increasing mean annual precipitation, suggesting a systematic change in the source of plant-available N (NH4 versus NO3) with climate. Nitrogen isotopes can reflect time integrated measurements on the controls of N storage in undisturbed areas that are critical for predictions of how these ecosystems would respond to human-mediated disturbances of the global N cycle.
Submetido por Gabriela Bielefeld Nardoto em 17-MAR-2004
Tema Científico do LBA: CD (Armazenamento e Trocas de Carbono)