A simple calibrated model of Amazon rainforest productivity based on leaf biochemical properties

Abstract

A simple 'big leaf ecosystem gas exchange model was developed, using eddy covariance data collected at an undisturbed tropical rainforest in south-western Amazonia (Brazil). The model used mechanistic equations of canopy biochemistry combined with an empirical stomatal model describing responses to light, temperature and humidity. After calibration, the model was driven using hourly data from a weather station at the top of the tower at the measurement site, yielding an estimate of gross primary productivity (annual photosynthesis) in 1992/1993 of about 200 mol C m~^ year"\ Although incoming photon flux density emerged as the major control on photosynthesis in this forest, at a given PAR CO2 assimilation rates were higher in the mornings than in the afternoons. This was attributable to stomatal closure in the afternoon in response to increasing canopy-to-air vapour pressure differences. Although most morning gas exchange was clearly limited by the rate of electron transport, afternoon gas exchange was generaWy observed to be very nearly co-limited by both Rubisco activity (V^^^) and electron transport rate. The sensitivity of the model to changes in nitrogen allocation showed that the modelled ratio of V^^^^ to electron transport (•/max) served nearly to maximize the annual carbon gain, and indeed, would have resulted in almost maximum annual carbon gain at the pre-industrial revolution atmospheric CO2 concentration of 27 Pa. Modelled gross primary productivity (GPP) was somewhat lower at 27 Pa, being about 160mol C m~^ year"'. The model suggests that, in the absence of any negative feedbacks on GPP, future higher concentrations of atmospheric CO2 will continue to increase the GPP of this rainforest, up to about 230 mol C m"^ year' at 70 Pa.

Response of central Siberian Scots pine to soil water deficit and long‐term trends in atmospheric CO2concentration

“…However, for aerodynamically rough needle leaf canopies, it can be expected that r b and r à b are relatively low. Making the assumption that r b and r à b can be ignored, as is effectively done in the simplified models of Lloyd [1991], Berninger and Hari [1993], and Lloyd et al [1995], allows considerable simplification. Equation (A3) then becomes…”

“…To estimate the values of these parameters we utilized data from eddy flux measurements of whole forest and ground CO 2 and H 2 O fluxes that have been conducted since 1998 at Zotino (see Table 2). Canopy values for the input parameters could be derived by fitting the combined conductance-assimilation model to data of forest photosynthesis [Arneth et al, 1999;Lloyd et al, 1995] that were obtained from the difference between measured whole forest-atmosphere CO 2 exchange minus ground CO 2 flux (Table A1). Data from 5 days collected between May and July 1999 were chosen to fit the model Wirth et al [1999].…”

Inverse estimation of Vcmax, leaf area index, and the Ball‐Berry parameter from carbon and energy fluxes

“…As several research groups point out [Lai et al, 2000;Lloyd et al, 1995], most models have converged on approaches that use (1) a mechanistic biochemical model of leaf carbon fixation [Farquhar et al, 1980] with variations provided by Harley and Tenhunen [1991], (2) an empirical model of stomatal control, especially the widely validated BallBerry equation [Collatz et al, 1991], and (3) often a mechanistic physical treatment of radiation penetration and absorption at the canopy level where energy balance is considered [de Pury and Farquhar, 1997;Norman, 1993;Sinclair et al, 1976;Wang and Leuning, 1998]. …”

Analyzing latent heat fluxes of coniferous forests with fuzzy logic

“…For evapotranspiration only a widely used approach is the combination of the Penman-Monteith equation with the Jarvis-Stewart canopy conductance model [Jarvis, 1976;Stewart, 1988]. This latter approach and also models that use simplified versions of elaborate bottom up models are constructed from the "single big leaf' concept, which considers a forest canopy as a giant leaf for which the same influencing variables and responses exist as for a "normal" leaf [Lloyd et al, 1995].…”