XVI International Botanical Congess

Net exchange of water, energy, and carbon dioxide is being measured in lowland wet forest at La Selva, Costa Rica. The eddy covariance system is based on an infrared gas analyzer with the sample inlets and a sonic anemometer mounted on a 42m tower. Concurrent measurements include meteorological factors for energy balance, continuous sampling of carbon dioxide, water,and air temperature at six heights,and primary production in replicated plots. The forest does not appear to light saturate at ambient light levels. Data from the 98 ENSO dry season showed no soil moisture limitation of carbon uptake. Wet season measurements also suggest that vapor pressure deficit does not strongly limit uptake. Daytime uptake increases with temperature. Forest carbon uptake in 1998 was constrained by light and temperature but not water.