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Comparing global models of terrestrial net primary productivity (NPP): analysis of differences in light absorption and light-use efficiency

Authors

  • A. Ruimy,

    1. Laboratoire d’Ecophysiologie Végétale, Bâtiment 362, Université Paris-Sud, F-91405 Orsay Cedex, France,
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  • L. Kergoat,

    1. Centre d’Etudes Spatiales de la Biosphère, bpi 2805, 18, Av Edouard Belin, F-31055 Toulouse Cedex, France,
    2. Present address: Laboratoire d’Ecologie Terrestre, 13, Av Col Roche, BP 4403, F-31405 Toulouse Cedex 4, France,
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  • A. Bondeau,

    1. Potsdam Institut für Klimafolgenforschung e.V. (PIK), Postfach 60 12 03, Telegrafenberg, D-14412 Potsdam, Germany
    2. Previous name: A. Fischer.
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  • ThE. Participants OF. ThE. Potsdam NpP. Model Intercomparison

    1. The following participated in the Potsdam NPP Model Intercomparison: A. Bondeau (previous name: A. Fischer), G. Churkina, W. Cramer, G. Colinet, J. Collatz, G. Dedieu, W. Emanuel, G. Esser, C. Field, L. François, A. Friend, A. Haxeltine, M. Heimann, J. Hoffstadt, J. Kaduk, L. Kergoat, D. W. Kicklighter, W. Knorr, G. Kohlmaier, B. Lurin, P. Maisongrande, P. Martin, R. McKeown, B. Meeson, B. Moore III, R. Nemani, B. Nemry, R. Olson, R. Otto, W. Parton, M. Plöchl, S. Prince, J. Randerson, I. Rasool, B. Rizzo, A. Ruimy, S. Running, D. Sahagian, B. Saugier, A. L. Schloss, J. Scurlock, W. Steffen, P. Warnant, and U. Wittenberg.
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Dr L. Kergoat, fax: + 33–5-61558544, E-mail: kergoat.let@cesbio.cnes.fr

Summary

Twelve global net primary productivity (NPP) models were compared: BIOME3, CASA, CARAIB, FBM, GLO-PEM, HYBRID, KGBM, PLAI, SDBM, SIB2, SILVAN and TURC. These models all use solar radiation as an input, and compute either absorbed solar radiation directly, or the amount of leaves used to absorb solar radiation, represented by the leaf area index (LAI). For all models, we obtained or estimated photosynthetically active radiation absorbed by the canopy (APAR). We then computed the light use efficiency for NPP (LUE) on an annual basis as the ratio of NPP to APAR. We analysed the relative importance for NPP of APAR and LUE. The analyses consider the global values of these factors, their spatial patterns represented by latitudinal variations, and the overall grid cell by grid cell variability. Spatial variability in NPP within a model proved to be determined by APAR, and differences among models by LUE. There was a compensation between APAR and LUE, so that global NPP values fell within the range of ‘generally accepted values’. Overall, APAR was lower for satellite driven models than for the other models. Most computed values of LUE were within the range of published values, except for one model.

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