Opened 7 years ago

Closed 3 years ago

Last modified 3 years ago

#138 closed defect (fixed)

suppress CO2 downregulation for C4 grassland

Reported by: nicolasviovy Owned by: peylin
Priority: major Milestone:
Component: Biogeochemical processes Version: trunc
Keywords: Cc:

Description

In constante_mtc the default value for downregulation_co2_coeff_mtc (which is used to calculate the effect of downregulation of CO2) for mtc 11 (C4 grassland) is set to 0.26 as for mtc 10 (C3 grassland). This is not correct as C4 been saturated at current CO2 there is no reason to apply the downregulation. The result is a large decrease of GPP in the future as the vcmax decrease is not compensated by the CO2 fertilization. So I think this value should be set to 0 for mtc 11 or at least a small value (as in fact there is a small indirect fertilization effect thru increasing WUE. then to take into account for the nitrogen limitation, a small value can be given for instance 0.03
before correcting and close the ticket would like to check if everybody agree ?

Change History (3)

comment:1 Changed 5 years ago by peylin

  • Owner changed from somebody to peylin
  • Status changed from new to accepted

comment:2 Changed 3 years ago by jgipsl

  • Resolution set to fixed
  • Status changed from accepted to closed

Done in the trunk rev [4655]

comment:3 Changed 3 years ago by peylin

The problem has been fixed with

  • setting the value for the parameter "downregulation_co2_coeff_mtc" to 0.03 for the two PFTs that correspond to C4 plants (natural and crops):

Additionally another parameter has been changed: DOWNREGULATION_CO2_BASELEVEL (in constante.f90); Initially this parameter was set to pre-industrial values (280 ppm) while it should be set at 380 ppm which is the atmospheric CO2 concentration that corresponds to "condition" where most Vcmax_25 values are derived (values prescribed to the system).

Philippe P.

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