Wood and soil-atmosphere CO2 fluxes from a tropical forest ecosystem / by Evilene C. Lopes.

Tese (doutor)- University of New Hampshire, 2005

Carbon cycling in tropical rainforests is an important component of the global carbon budget. A better understanding of controlling mechanisms and magnitude of CO2 sources from tropical forests will improve our ability to predict future impacts of climate changes. The research presented in this dissertation has focused on determining the magnitude and characteristics of the CO2 flux from tropical wood and soil surfaces. Stem CO2 fluxes were measured in a tropical moist forest at Tapajos National Forest (TNF) in Brazil and in a tropical wet forest at La Selva Biological Station in Costa Rica (LS) using infrared gas analysis methods. Annual stem CO2 fluxes for TNF and LS averaged 1.7 + 0.1 ƒÊmol m-2 s-1 and 1.5 + 0.1 ƒÊmol m-2 s-1, respectively. At TNF wood surface area was calculated (4161 m2 ha-1) and wood CO2 flux extrapolated to ground area resulted in an annual flux of 259 g C m-2 yr-1. Soil-atmosphere CO2 fluxes were measured at TNF using infrared gas analysis methods. Line sampling of soil CO2 fluxes made on randomly placed 30 meters transects averaged 4.7 + 0.2 ƒÊmol m-2 s-1 with higher rates during the wet season (4.9 + 0.3 ƒÊmol m-2 s-1) than during the dry season (4.4 + 0.2 ƒÊmol m-2 s-1). Fluxes were weakly correlated with precipitation and not correlated with soil moisture or temperature. Geostatistical analysis of grid sampling of soil CO2 fluxes indicated that they were not spatially dependent. Fluxes measured during wet season and dry season on grid sampling averaged 5.6 + 0.2 ƒÊmol m-2 s-1 and 4.5 + 0.1 ƒÊmol m-2 s-1, respectively. The estimated annual average of soil surface CO2 flux for the TNF was 1780 g C m-2 yr-1. Assuming that root and heterotrophic respiration each contribute about 50% of soil CO2 efflux, then approximately 890 g C m-2 yr-1 derive from each source. The estimated gross primary photosynthesis for the TNF is 3000 g C m-2 yr-1 (Miller et al., 2004). Therefore, estimated contribution of wood and root CO2 flux to the GPP are respectively 8.7% and 15%.