Plant "excess respiration" not removed from NEP/NPP in FATES

[walkeranthonyp]

Hi team,

In our simulations with FATES at FACE experiments and transient runs at Lambir we've found that the output variables FATES_NEP and FATES_NPP do not include plant excess respiration. Presumably this also affects other NPP output variables.

Excess respiration is respiration in FATES-CNP when allocatable carbon is available but nutrients limit any further growth and carbon storage pools are at their maximum, calculated here.

The FATES_NPP and the plant side of FATES_NEP are calculated here as a function of ccohort%npp_tstep.

ccohort%npp_tstep is calculated here in FatesPlantRespPhotosynthMod.F90. Pretty clear that this is just taking maintenance and growth respiration into account.

Flagging here for thoughts and what to watch out for in any fix. It seems like it could just be done in the history variable processing but excess resp would also need to be calculated with the same indexing as all the various NPP variables.

Are there other things that rely on the ccohort%npp_tstep variable in their calculation? Might it be better to update that in the parteh subroutines when they execute? If yes, presumably this woudl affect the C balance error checking on the ELM side, and maybe FATES too.

Interestingly, both for FATES and Lambir simulations the NPP values without excess respiration removed give a better fit to some of the data. Probably for different reasons. But that's a conversation perhaps for a different thread.

Note: NEE on the ELM side does have excess respiration included. Not checked NPP.
Also note: the C balance checks are fine, this is from running versions of the model with no errors.