Testing a Mechanistic Model of Forest-Canopy Mass and Energy Exchange Using Eddy Correlation: Carbon Dioxide and Ozone Uptake by a Mixed Oak-Maple Stand

Abstract

A big-leaf model of C3-canopy mass and energy exchange was used to predict hourly C02 and O3 uptake by a mixed deciduous Quercus-Acer (oak-maple) stand in central Massachusetts, USA. The model is based on canopy-radiation interactions, leaf mesophyll metabolism (photosynthetic electron transport, carboxylation and oxygenation of ribulose 1,s-bisphosphate [RuP2] by RuPz carboxylase/oxygenase [Rubisco], and respiration), physical transport conductances of mass and heat above and within the canopy, conductances of mass at the leaf surface and in the mesophyll, and mass and energy exchange at the soil surface (forest floor). Predictions of hourly C02 and O3 uptake were compared to independent whole-forest C02 and O3 exchange measurements made by the eddy correlation method during a 68 day period in the summer and early autumn of 1992. Predicted hourly C02 exchange rate was strongly correlated (r --+0.91) with measured hourly COz exchange, but mean day-time predicted whole-forest C02 uptake was c. 13% (c. 1.13 pmol C 0 2 m-2 s-') greater than C 0 2 uptake measured by eddy correlation. The model tended to overpredict C02 uptake during late afternoon, but was accurate during the rest of the day. Predicted and measured O3 uptake rates also were positively correlated (r * +0.76). The diurnal patterns of predicted and measured O3 uptake indicated that stomata1 conductance (g,) was accurately predicted during the morning, but in the afternoon the model overpredicted g,. This pattern was consistent with the overprediction of afternoon C 0 2 uptake, and suggested that a feedback inhibition of photosynthesis occurred in the afternoon. This might have been related to source-sink imbalance following several hours of photosynthesis. On the whole, and in spite of the simplifications inherent in the big-leaf representation of the canopy, the model is useful for predicting forest-environment interactions and for interpreting mass and energy exchange measurements.

Environmental controls on the photosynthesis and respiration of a boreal lichen woodland: a growing season of whole-ecosystem exchange measurements by eddy correlation

“…We developed a mechanistic model of forest carbon assimilation following the approach outlined by Amthor et al (1994). We parameterized the carbon assimilation module of the Amthor model for the Schefferville site using field observations from a nearby stand, and compared model results with the eddy flux measurements.…”

An analytical model of non‐photorespiratory CO2 release in the light and dark in leaves of C3 species based on stoichiometric flux balance

“…Photosynthesis is usually predicted in C3 plants by the model of Farquhar, von Caemmerer & Berry (1980) (FCB), whereas respiration is usually predicted empirically, for example, as a function of leaf nitrogen or ribulose 1·5-bisphosphate carboxylase/ oxygenase (Rubisco) content (Williams et al 1996;de Pury & Farquhar 1997), as a constant fraction of gross carbon gain (Waring, Landsberg & Williams 1998;DeLucia et al 2007), as a function of tissue pool size (Running & Coughlan 1988) or in relation to phenological state, based on empirical partitioning of respiration into growth and maintenance terms (Thornley 1970;Amthor et al 1994). …”

Assessing the Impact of Canopy Structure Simplification in Common Multilayer Models on Irradiance Absorption Estimates of Measured and Virtually Created Fagus sylvatica (L.) Stands

“…These radiation transfer models simulate the effect of canopy geometry and structure on light interception and can link individual leaf light capture to gross photosynthetic assimilations [3][4][5][6][7]. However, because of the difficulties in acquiring detailed stand structure information, most of these models simplify the canopy structure, by using either big-leaf models [8][9][10] (single leaf assumption), or multi-layer models [11][12][13][14] (homogeneous horizontal and vertical layers containing the same amount of leaf area). These simplifications may lead to inaccurate simulations of light interception at the canopy and subsequently at the leaf level [15].…”