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

Soil properties and carbon sequestration along a toposequencein central Amazonia forestRegina C. C. Luizão; Lucinéia S. Souza, Fabiane L. Oliveira & Flávio J. LuizãoDepartamento de Ecologia, Instituto Nacional de Pesquisas da AmazôniaCaixa Postal 478, 69011-970, Manaus, AM. rccl@inpa.gov.brAbstractRecent studies suggest that soil topography and texture might be influencing the amount ofC being sequestred by the forest as measured by eddy flux. Carbon dioxide measured bythat technique also does not identify the gas source, wether from soil or from plants.Aiming to contribute in filling this gap, the present study made a physical-chemical andbiological characterization of the soil along a toposequence in the surrounds of theclimatological tower in order to relate them with the CO2 measurements from the tower.The study was carried out in the ZF-2 Reserve, located 60 km north of Manaus. Along thetoposequence, three replicate plots were selected in each topographic position: plateau,slope and valley. In each plot, three composite samples made up of five soil cores werecollected from the topsoil (0-12 cm). Soil measurements included texture, pH, soil organicmatter, moisture, microbial biomass carbon and nitrogen transformation rates. Clay contentwas the most distinct factor varying along the toposequence with 65% in the plateau, 43%in the slope and 5% in the valley, a pattern followed by the soil organic matter with 6%, 3%and 1,5% and soil moisture with 28%, 21% and 15% respectively in these positions.Despite these differences, soil biological properties such as soil respiration, microbialcarbon and nitrogen did not change significantly along the toposequence. For soil pH andmicrobial transformations of nitrogen the differences were only related to the valleyposition, with significantly lower nitrate and rates of nitrification even though the soil pHwas higher when compared with the other two topographic positions. Relationship betweenthese soil properties and carbon sequestration by the forest measured by eddy flux will bedicussed.