Effects of Climate Factors on Daytime Carbon Exchange From an Old Growth Forest in Costa Rica

Abstract

Eddy covariance measurements of CO₂, H₂O, and heat were conducted in tropical lowland wet orest at the La Selva Biological Station in Costa Rica. The system was based on a closed-path infrared gas analyzer with the sample inlets and sonic anemometer mounted on a 42-m tower. Prevailing winds were easterly from the Caribbean with little anthropogenic influence. The tower footprint was primary upland forest. Concurrent measurements included standard micrometeorological sensors for energy balance and six levels of continuous canopy profile sampling for CO₂, H₂O, and air temperatures. Canopy roughness at the site is very high and may contribute to mixing at low wind speeds. Data are presented for 39 days of daytime CO₂ fluxes. Carbon dioxide fluxes at high irradiances ranged from —10 to —20 μmol m² s⁻¹. The response of CO₂ fluxes to solar radiation was curvilinear and did not saturate under ambient irradiance regimes. No effects of vapor pressure deficit on ecosystem carbon exchange were detected during the study period. Temperature, however, appeared to affect daytime carbon exchange slightly. The results suggest that solar radiation input is the primary limiting climatic factor for carbon uptake.