Diurnal CO 2 exchange and photosynthesis of the Samoa tropical forest

The exchange of CO 2 between the atmosphere and tropical forest ecosystem of American Samoa was continuously monitored for 3 days in December 1988. The island was modeled as a simple wind‐ventilated respiration chamber with CO 2 input concentration, CO 2 output concentration, and residence time as measured variables. Net ecosystem production rates were calculated by incorporating Gaussian vertical diffusion into the model. Nighttime respiration averaged 0.34 (±0.06) g C m −2 h −1 ; peak midday uptake was 0.85 (±0.23) g C m −2 h −1 . Thirty‐nine percent (±30%) more carbon was assimilated by the ecosystem during the day than was released at night. The diurnal net ecosystem production averaged 1.5 g C m −2 d −1 . The daytime CO 2 exchange rate varied as the logarithm of incident solar radiation over a range of 30 W/m 2 to 900 W/m 2 , with r 2 = 0.87. Total ecosystem respiration equaled photosynthesis at a radiation intensity of 72 (±14) W/m 2 . The saturation intensity was 600 W/m 2 .