Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 6 7 2009 10.5194/bg-6-1247-2009 http://www.biogeosciences.net/6/1247/2009/ http://www.biogeosciences.net/6/1247/2009/bg-6-1247-2009.html http://www.biogeosciences.net/6/1247/2009/bg-6-1247-2009.pdf 1247 1272 2009-07-28 Modelling basin-wide variations in Amazon forest productivity – Part 1: Model calibration, evaluation and upscaling functions for canopy photosynthesis L. M. Mercado lmme@ceh.ac.uk J. Lloyd A. J. Dolman S. Sitch S. Patiño Centre for Ecology and Hydrology, Wallingford, Oxon, OX10 8BB, UK Max Planck Institute for Biogeochemistry, 07745 Jena, Germany School of Geography, University of Leeds, LS2 9JT, UK Free University of Amsterdam, 1081 HV Amsterdam, The Netherlands Met Office Hadley Centre, JCHMR, Wallingford, Oxon, OX10 8BB, UK Instituto de Investigación de Recursos Biológicos Alexander von Humboldt, Diagonal 27 No. 15-09, Bogotá D.C, Colombia Given the importance of Amazon rainforest in the global carbon and hydrological cycles, there is a need to parameterize and validate ecosystem gas exchange and vegetation models for this region in order to adequately simulate present and future carbon and water balances. In this study, a sun and shade canopy gas exchange model is calibrated and evaluated at five rainforest sites using eddy correlation measurements of carbon and energy fluxes. <br><br> Results from the model-data evaluation suggest that with adequate parameterisation, photosynthesis models taking into account the separation of diffuse and direct irradiance and the dynamics of sunlit and shaded leaves can accurately represent photosynthesis in these forests. Also, stomatal conductance formulations that only take into account atmospheric demand fail to correctly simulate moisture and CO₂ fluxes in forests with a pronounced dry season, particularly during afternoon conditions. Nevertheless, it is also the case that large uncertainties are associated not only with the eddy correlation data, but also with the estimates of ecosystem respiration required for model validation. To accurately simulate Gross Primary Productivity (GPP) and energy partitioning the most critical parameters and model processes are the quantum yield of photosynthetic uptake, the maximum carboxylation capacity of Rubisco, and simulation of stomatal conductance. <br><br> Using this model-data synergy, we developed scaling functions to provide estimates of canopy photosynthetic parameters for a range of diverse forests across the Amazon region, utilising the best fitted parameter for maximum carboxylation capacity of Rubisco, and foliar nutrients (N and P) for all sites. Aranibar,~J N., Berry,~J A., Riley,~W J., Pataki,~D E., Law,~B E., and Ehleringer,~J R.: Combining meteorology, eddy fluxes, isotope measurements, and modeling to understand environmental controls of carbon isotope discrimination at the canopy scale, Glob. Change Biol., 12, 710–730, 2006. 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