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On photosynthesis parameters for the A-gs surface scheme for high vegetation

G.J. Steeneveld

A review of plant physiological based surface schemes is presented. For forest, it appeared that the so called A-gs scheme assimilated too fast compared to the MOSES scheme used in the Hadley Centre climate model. In addition, the photosynthesis parameter Ve,max in the A-gs scheme measured in the field appeared to be a factor 2 lower than derived from laboratory experiments.
Field measurements in Scots Pine (C3, Pinus sylvestris) were used to calibrate the ratio of intern to extern COz concentration as function of vapour pressure deficit at leaf surface. Also lemar and
the mesophyll conductance has been calibrated, which resulted in Ve max = 2.0 mg/m'/ and gm = 3.2 mm/s. This is a factor 2 lower than the standard values in the A-gs scheme, but in agreement with literature values based on field experiments. Eventually a new parameter set is proposed for high vegetation for both C3 and C4 plants.
One dimensional model simulation using a tiled representation of the surfade resulted in a quite good simulation of both seasonal and monthly averaged diurnal cycles of latent and sensible heat flux for Scots pine. CO2 flux density calculations showed proper amplitudes, but some phase shift due to the time lag introduced by CO2 storage change.
The robustness of the parameter values across three different forests field data sets was tested in a Monte Carlo approach. A unique parameter combination could not be found within the forest.
Contrary, an area of acceptable parameter sets was present. It appeared that the considered forests did not have a parameter set in common. Especially boreal forests tend to have a dissent parameter set. This may be due to nutrient deficiency.

Bibliografische gegevens

G.J. Steeneveld. On photosynthesis parameters for the A-gs surface scheme for high vegetation
KNMI number: TR-242, Year: 2002, Pages: 79

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