Carbon dioxide transfer over a Central Amazonian rain forest

Tropical rain forests are among the most important and least monitored of t errestrial ecosystems. In recent years, their influence on atmospheric conc entrations of carbon dioxide and water vapor has become the subject of much speculation. Here we present results from a yearlong study of CO2 fluxes. at a tropical forest in central Amazonia, using the micrometeorological tec hnique of eddy covariance. The diurnal cycle of CO2 flux was consistent wit h previous shortterm studies in tropical rain forests, implying that the Am azonian rain forest shows a fair degree of spatial uniformity in bulk ecoph ysiological characteristics. Typical peak daytime photosynthesis rates were 24-28 mu mol CO2 m(-2) s(-1), and respiration rates were 6-8 mu mol CO2 m( -1) s(-1). There was significant seasonality in peak photosynthesis over th e year, which appeared strongly correlated with soil moisture content. On t he other hand, there was no evidence of strong seasonality in soil respirat ion. Central Amazonia has only a short, 3 month dry season, not atypical of tropical rain forest, and it is therefore likely that large areas of Amazo nia exhibit significant seasonality in photosynthetic capacity. The gross p rimary production was calculated to be 30 t C ha(-1) yr(-1). An analysis of data quality is included in the appendix.