9315697 Sternberg Isotopic composition and concentration of water vapor and ambient carbon dioxide will be determined at various heights in two tropical rain forests, (a seasonal and an aseasonal forest), during the day and night. Isotopic values of these gases will be compared with that of potential sources: soil respiration, and atmospheric for carbon dioxide; and soil evaporation, transpiration, and atmospheric for water vapor. These measurements will answer the following questions about carbon dioxide and water cycling in the Amazonian rain forest: What levels of the soil profile provide water for tropical trees in the Amazonian forest? What is the contribution of soil evaporation, transpiration, and atmospheric moisture to the ambient humidity in the forest? What is the amount of respired carbon dioxide refixed by photosynthesis? How is the oxygen isotopic composition of ambient carbon dioxide influenced by equilibration with leaf water during photosynthesis? The answers to these questions will advance our knowledge on the dynamics of carbon dioxide and water cycling in the largest stand of continuous forest in the world; the Amazon.
