Efluxo de CO₂ do solo e biomassa de raízes finas ao longo de um gradiente topográfico na Floresta de Caxiuanã-PA

Abstract

The objective of this research was to understand the role of small topographic elevations in the soil carbon dioxide (CO2) efflux comparing different seasonal period in the National Forest of Caxiuanã, oriental Amazon. Were selected two transects with about 17m topographic gradient, the first initiated near the border of a permanent stream and the second standing near an intermittent stream, denominate in this work as Transect1 and Transect2, respectively. In each transect were selected four locations for the collection and measurement of data called lowland, middle lowland, middle plateau and plateau. At these sites were conducted CO2 efflux and soil temperature analysis, and soil samples for organic carbon analysis and fine root (<2 mm) biomass studies at different depth intervals. It was observed a significant difference in the soil organic carbon concentration compared in the soil surface layer (0-10 cm) in lowland topography, where the transect that begins in the board of the intermittent stream had the significantly higher organic carbon content. It was also observed a soil organic carbon reduction with depth, but there were no differences in organic carbon content with topographic variation. Bringing together both transects, the results related to superficial fine root biomass, it was found mean values of 382.47 ± 25.46 g m-2 for the dry months and 298.24 ± 23.50 g m-2 for the rainy months. In general there was a reduction in fine root biomass by increasing the soil depth, and in the surface layer (0-30 cm) is concentrated to greater root biomass with more than 80% of total root biomass for both transects. There were significant differences in root biomass among and within transects. For the same time, it was founded higher CO2 efflux in the lowland topography compared to the plateau. Seasonal variation also has effect on soil CO2 efflux, with the month of August (transitional month) having the highest CO2 effluxes and March (rainy month) the lowest CO2 efflux, independent of topographic position.