A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Autotrophic X heterotrophic respiration in Western Amazonia, Acre-BrazilCI Salimon; JW Pereira; Victoria, RL; EA Davidson; AWF Melo; IF BrownConversion of forest to cattle pastures and subsequent abandonment of those pastures isoccurring throughout the Amazon Basin, and although there is a lot of research on theconsequences that come from this land cover change, there are still many questions to beanswered about biogeochemical processes associated with them. In this study we try todetermine the effects of land-use change on soil respiration in pastures, secondary forestsand mature forests near Rio Branco, Acre. Data analyses from June/99 to July/00 showsthat the greatest CO 2 fluxes are observed in pastures and not in mature forests. In searchof a better understanding of these results, we sampled soils for carbon stocks down to60cm depth and conducted some respirometry essays, and also sampled CO 2 fordetermination of its δ 13 C value, by using keeling plots. Carbon stocks are higher inpastures than in mature and secondary forests. Heterotrophic respiration is lower or equalin pasture compared to primary and secondary forests, showing that autotrophicrespiration is probably the main cause of higher fluxes in pastures. δ 13 C of heterotrophicrespired CO 2 in pasture was -15‰. Since δ 13 C from pasture soil is -21‰,microorganisms in the pasture soil are feeding basically on carbon from grasses and notfrom remaining forest carbon.