A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

An attempt to model Manaus k34, k14 and Caixuana eddy covariance data witha big-leaf and sun/shade modelLina Mercado 1* , Jon Lloyd 2 , Bart Kruijt 3 , Yadvinder Mahli 4 and Antonio Nobre 5 .1,2Max Planck Institute for Biogeochemistry, Jena,Germany.Carl-Zeiss-Promenade 10, 07745 Jena, Germany*Author for correspondence: lmercado@bgc-jena.mpg.de2e-mail : jon.lloyd@bgc-jena.mpg.de3 Alterra, University of Wageningen Research, Wageningen, The Netherlandse-mail : B.Kruijt@Alterra.wag-ur.nl4 University of Edinburgh, Institute of Ecology and Resource Management, Edinburgh, Scotlande-mail: ymalhi@srv0.bio.ed.ac.uk5Instituto Nacional de Pesquisas da Amazônia, Manaus, Amazonas, Brazile-mail: anobre27@yahoo.comEddy covariance data from the Manaus K34 (1999-2000), K14 (1995-1996) and Caixuana(1999) towers in the Brazilian Amazon have been used in an intent of parameterization of twoecosystem gas exchange models. Those models use the big- leaf (Lloyd et al, 1995) and a sunand shade (De Pury and Farquhar, 1997) approaches for canopy photosynthesis modeling.The main difference between these two models lays in the way they represent the response ofcanopy photosynthesis to irradiance. The big leaf model assumes that the distribution ofphotosynthetic capacity is proportional to the profile of absorbed irradiance. In the sun/shademodel, the sunlit and shaded fractions of the canopy change during the day making theirradiance absorption and the photosynthetic capacity of both fractions to change as well.However, the goodness of fit with the sun/shade model did not improve very much comparedto the big-leaf model using the Manaus K14 data.Parameterization of the models for the Manaus K14 data during 1995-1996 seem to indicateseasonality of the photosynthetic parameters for canopy rubisco activity (Vmax ) and the lightsaturatedelectron transport capacity (Jmax ). Vmax and Jmax present a decrease during the dryseason. But it is not clear if this is attributable to changes in leaf area, photosynthetic capacityor both.Calibration of the models against Manaus K34 data has been problematic due to a lot ofscatter in the data together with some none yet explainable measurements of very low valuesof Net ecosystem exchange at high irradiances.Caixuana data fit well to both model types without requiring any seasonality in thephotosynthetic parameters observed for the Manaus K14 data.ReferencesLloyd, J., Grace, J., Wong, S.-C., Miranda, A.C., Meir, P., Miranda, H.S., Wright, I.R.C., andMacIntyre, J.A.(1995). A simple calibrated model of Amazon rain forest productivity based on leafbiochemical properties. Plant, Cell and Environment 18, 1129-1145.De Pury, D.G.G., and Farquhar, G.D.(1997). Simple scaling of photosynthesis from leaves to canopieswithout the errors of big-leaf models. Plant, Cell and Environment, 20, 537-557.