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

ANNUAL PATTERNS OF SOIL CO 2 EMISSIONS FROM BRAZILIAN FORESTSAND PASTURESPaul A. Steudler* 1 , Brigitte J. Feigl 2 , Diana C. Garcia-Montiel 1 , Jerry M. Melillo 1 ,Christopher Neill 1 , Marisa C. Piccolo 2 & Carlos C. Cerri 21 The Ecosystems Center, Marine Biological Laboratory, Woods Hole, Massachusetts,02543, U.S.A.2 Centro de Energia Nuclear na Agricultura, CENA/USP, CP 96, 13416-000 Piracicaba,SP, Brasil.steudler@mbl.edueduardo@cena.usp.brdgarcia@mbl.edujmelillo@mbl.educneill@mbl.edumpiccolo@cena.usp.brcerri@cena.usp.brSoil carbon dioxide (CO 2 ) effluxes and soil physical and chemical properties weremeasured intensively over a 19-month period in two sequences that consisted of forestand pastures ranging in age from four to 41 years old in Rondônia in the southwesternregion of the Amazon Basin. Furthermore, we created a new pasture directly from forestand measured the emission of CO 2 and other properties over 27 months. Maximum soilrespiration rates were measured during the wet season in both forests and pastures. Plantphenology, such as the timing of maximum root biomass and the asynchrony of aboveandbelow-ground litter inputs and subsequent decomposition, may play an important rolein determining the seasonally of the observed respiration rates. Average annual CO 2release from the forests was 1,347 g C/m 2 . Annual releases from the pastures rangedfrom 1,090 to 2,365 g C/m 2 and increased with pasture age for the first six years afterestablishment, but then remained nearly constant at about 1,750 g C/m 2 for the next twodecades. Soil moisture was a strong predictor of seasonal CO 2 emissions from all sites