Unit in the carbon cycle

[byzheng]

The unit in the model is fine (every thing is DM) if we don't have respiration.

However, the unit of carbon cycle is not clear when ConversionEfficiency and MaintenanceRespiration are not equal 1 and 0, respectively. So I will suggest to clarify the unit in the carbon cycle after discussing with @EnliWang .

• Biomass in the structural, storage and metabolic components of all organs: DM
• Maintenance respiration: CO2
• Growth respiration: CO2
• Photosynthesis: CH2O

See here for a diagram about carbon cycle and the conversion in different process.

The changes will not impact on any models without respiration.

@HamishBrownPFR and @EnliWang Any comments about it?

[byzheng]

@hol353. I would like to add extra variables for class Biomass to convert biomass unit from DM into other units (e.g. C, CO2, CH2O) for carbon cycle. I think the best places to add these codes are in the class Biomass. However, It will require an extra parameter CarbonConcentration which is different for each organ.

My question is how I should pass the organ specific parameter CarbonConcentration into Biomass class. Do you have an alternative way to implement this?

[hol353]

I would like @hut104 to comment on this as well.

[byzheng]

After discussion with @EnliWang, we proposed to move Maintenance Respiration into CanopyPhotosynthesis, i.e. deleting all codes related Maintenance respiration in all organs. This method is similar with Gaudriaan and Van Laar (1994). @HamishBrownPFR Let me know if you have any comments.

1. Goudriaan, J.; Van Laar, H. H. Modelling Potential Crop Growth Processes; Current Issues in Production Ecology; Springer Netherlands: Dordrecht, 1994; Vol. 2; ISBN 978-0-7923-3220-6.

[hut104]

We should probably had a discussion on all of this after the Christmas break. There is talk of the biomass class being used by non-crop models (ie soil models), and we need to think about oil crops soon, and I'm not entirely sure what the impacts will be for information passing to the canopyphotosynthesis model. The potential simplicity of the approach is tempting though. It might be good, and might simplify the arbitrator. However, I'd be keen to talk it over to see if it is not too simple, or has impacts in other places.

[byzheng]

Thanks Neil. Can organise a meeting after New year to discuss it. When Enli and I discussed about the implementation, we already consider the oil crops. I may start to implement our thoughts and test what's impact for other components.

[HamishBrownPFR]

@byzheng, I can think of applications where you would want to have maintenance respiration on an organ but not use the canopy photosynthesis model. For example the lucerne model will need root respiration to model seasonal patterns of root biomass but we are not planning to use the canopy photosynthesis model yet.
Generally we try to put stuff where it logically belongs and maintenance respiration is in the organs rather than in the function of canopy photosynthesis so it seems cleaner to put it there. However, pragmatism is good too.

[EnliWang]

It would be good to have a discussion after the Christmas break. What I suggested is to do the Maintenance respiration after photosynthesis, but before calculating the biomass growth rate of the organs, so that the remaining assimilates can be used for growth. Maintenance respiration should not be part of the canopy photosynthesis function. Maintenance respiration may still remain on an organ, but is calculated before rather than being subtracted from organ growth rate.

[HamishBrownPFR]

Ok, that makes sense. The best way to do that would be to include maintenance respiration as a step in the arbitrator, before other biomass allocation is done. Will be good to discuss this further in the new year.

Hamish

[rcichota]

I like the way this is going, separating photosynthesis and respiration is great for several reasons; if we can put the code in the places were is logical, then all the better. The scheme shown in the figure above is used in several models and is the case for AgPasture. To simplify the units there the photosynthesis, the two respirations, and the net growth were considered as units of Carbon only (g/m2 or kg/ha). The later isthen converted to DM and the simulation goes on. This seems simpler that using CO2 and CH2O...