Fluxes of carbon dioxide and water vapour over an undisturbed tropical forest in south‐west Amazonia

Abstract

1 Carbon dioxide and water vapour fluxes were measured for 55 days by eddy covariance over an undisturbed tropical rain forest in Rondonia, Brazil. Profiles of CO2 inside the canopy were also measured. 2 During the night, CO2 concentration frequently built up to 500 ppm throughout the canopy as a result of low rates of exchange with the atmosphere. In the early morning hours, ventilation of the canopy occurred. 3 Ecosystem gas exchange was calculated from a knowledge of fluxes above the canopy and changes of CO2 stored inside the canopy. Typically, uptake by the canopy was 15 |imol m"^ s"^ in bright sunlight and dark respiration was 6-7 pmol m^^ s"\ The quantum requirement at low irradiance was: 40 mol photons per mol of CO2. 4 Bulk stomatal conductance of the ecosystem was maximal in the early moming (0.4-1.0 mol m^^ s'^) and declined over the course of the day as leaf-to-air vapour pressure difference increased.

Coupled carbon-water exchange of the Amazon rain forest, II. Comparison of predicted and observed seasonal exchange of energy, CO<sub>2</sub>, isoprene and ozone at a remote site in Rondônia

“…The net fluxes of sensible heat, H 2 O, CO 2 , and ozone measured above the canopy have to be corrected by the canopy volume storage flux for a direct comparison with the model predicted "instantaneous" fluxes. The storage fluxes for CO 2 and ozone are calculated according to Grace et al (1995) from the temporal evolution of the diurnally averaged vertical concentration profiles. The empirical relationship of Moore and Fisch (1986), evaluated for RBJ-A by Rummel (2005), was applied to determine the energy storage terms, using the temperature and humidity observed above the canopy.…”

Coupled carbon-water exchange of the Amazon rain forest, I. Model description, parameterization and sensitivity analysis

“…The scheme we developed is mainly a synthesis of the original CANVEG model (Baldocchi and Meyers, 1998), the Lagrangian dispersion approach proposed by Raupach (1989) and the leaf-to-canopy integration scheme described by Leuning et al (1995). As far as we know there exist no further studies that explicitly model the coupled exchange of CO 2 and energy of Amazon rain forest canopies including the Lagrangian approach for turbulent exchange: There is the big leaf approach of Lloyd et al (1995), focusing mainly on CO 2 , and the multilayer soil-plant-atmosphere model of Williams et al (1998), coupling the water flow from the soil to the atmosphere with CFixation by including a detailed soil module. However, both models differ significantly from the CANVEG type since temperature and scalar gradients inside the canopy are neglected (no transport model included).…”

“…CO 2 fertilization) and to separate the influence of environmental and eco-physiological factors on trace gas exchange. Despite large data pools, being available from long-term and intensive regional studies (Grace et al, 1995;Gash et al, 1996;Sellers et al, 1997;Seufert et al, 1997;Halldin et al, 1999;Andreae et al, 2002;Gu and Baldocchi, 2002;Falge et al, 2002) for model parameterization, evaluation and application, only agricultural crops, and broad-leaved and coniferous forests in temperate regions have been investigated within a CANVEG model frame work (see Baldocchi and Harley, 1995;Baldocchi and Meyers, 1998;Baldocchi and Wilson, 2001;Lai et al, 2000a,b;Katul et al, 2003;Baldocchi and Bowling, 2003).…”

A System for the Measurement of Vertical Gradients of CO2, H2O and Air Temperature within and above the Canopy of Plant

“…The canopy storage change has been adequately accounted for as part of the net ecosystem exchange determination (Gu et al, 2005). The importance of CO 2 storage fl ux to the net ecosystem exchange is due to the accumulation of CO 2 within the canopy airspace during a calm night, which may be depleted in the early morning as the turbulence intensity increases (Grace et al, 1995). For the determination of CO 2 storage flux, it is very important to measure CO 2 concentration profile at different heights near the ground level (Gu et al, 2005).…”

“…However, micrometeorological systems made above the forest canopy have limitations. The measurement of CO 2 fl ux using the eddy covariance system does not always represent the net ecosystem exchange during the period of sampling (Ruimy et al, 1995;Grace et al, 1995;Wilson and Meyers, 2001). This is because of the CO 2 storage in the layer of air below the measurement level.…”