Nutrient competition

[jinmuluo]

Hi everyone,

I have one question about the nutrient competition with FUN open in the CLM.
I noticed that in the "SoilBiogeochemCompetitionMod.F90" module where CLM calculates the N competition between plant uptake, immobilization, nitrification and denitrification has two different variables that describe the nutrient to the plant. one is <sminn_to_plant_vr>, and the other one is < sminn_to_plant_fun_vr >, obvious, the latter one is the flux we use if we open the FUN model.
But in the code itself, it looks like < sminn_to_plant_fun_vr > is not the product flux after the nutrient competition but just from the FUN model patch level. I do see in the code, CLM only pass this module when < sminn_to_plant_fun_vr > is smaller than <sminn_to_plant_vr>, but does this mean the FUN model always predicts smaller plant uptake flux than the standard uptake scheme after nutrient competition?

 

[wwieder]

Hi Jinmu, I find these parts of the code confusing too. See what you think of this interpretation.

In src/soilbiogeochem/SoilBiogeochemCompetitionMod.F90, looks like if FUN is on then plants get a fraction of the NH4 that's available, after modifying for "actual" immobilization and nitrification fluxes. Then the same thing happens for NO3, with actual heterotrophic nitrate uptake and denitrification removed

Then FUN figures out how much it has to pay for taking up the available N in src/biogeochem/CNFUNMod.

Finally the N that FUN takes up is summed into sminn_to_npool here CTSM/src/biogeochem/NutrientCompetitionFlexibleCNMod.F90 at a5ef062adeeee560b1d3f3982f588da6b288e802 · ESCOMP/CTSM

I don't really know how to answer your question about FUN vs. the "standard uptake scheme", mainly because FUN is the standard uptake scheme for CLM5. Maybe you can ellaborate about what you're interested in figuring out here?

 

[jinmuluo]

Hi Jinmu, I find these parts of the code confusing too. See what you think of this interpretation.

In src/soilbiogeochem/SoilBiogeochemCompetitionMod.F90, looks like if FUN is on then plants get a fraction of the NH4 that's available, after modifying for "actual" immobilization and nitrification fluxes. Then the same thing happens for NO3, with actual heterotrophic nitrate uptake and denitrification removed

Then FUN figures out how much it has to pay for taking up the available N in src/biogeochem/CNFUNMod.

Finally the N that FUN takes up is summed into sminn_to_npool here CTSM/src/biogeochem/NutrientCompetitionFlexibleCNMod.F90 at a5ef062adeeee560b1d3f3982f588da6b288e802 · ESCOMP/CTSM

I don't really know how to answer your question about FUN vs. the "standard uptake scheme", mainly because FUN is the standard uptake scheme for CLM5. Maybe you can ellaborate about what you're interested in figuring out here?

Hi Will,

Thank you so much for your answer, the "standard uptake scheme" I meant in the initial question is the "plant_ndemand" which I thought was not from the FUN module.
My first guess was CLM calculates the "plant_ndemand" in the NutrientCompetitionFlexibleCNMod.F90, and then passes this "plant_ndemand" to the nutrient competition module to determine if "plant_ndemand" needs to be scaled down (where we get sminn_to_plant_vr ). At the same time, "plant_ndemand" has also been passed to the FUN module to determine the cost of N uptake and get the sminn_to_plant_fun_vr . Finally, I got the conclusion sminn_to_plant_vr is not equal to sminn_to_plant_fun_vr.
So I still don't know how the competition module affects FUN, could you help to answer this question? Thank you so much.

Best,

Jinmu