Improvement/Tuning of the modelling of the Autotrophic Respiration

[nvuilsce]

Since the inclusion of the N cycle into the trunk, the tuning of the autotrophic respiration has to be done, as it has been done with the version prior to ORCHIDEE_2.0 few months ago.
One particular focus should be put on the contribution of the labile C, which is partly respired, when it is in excess. Is it a feature/process one wants to keep or not ? If not, what do we do when labile C is excessively high ?

[luyssaert]

Possible solutions for this problem has been implemented in CN-CAN first.

• Growth and maintanance respiration have been rewritten in line with the available literature on the topic see r5959 and r5960.
• This rewrite requires that Rm is reparameterized. A first order estimate of acceptable parameters for coeff_maint_init is given in r5967 and r5968 (but these still need to be refined and tested over larger spatial domains see ticket #559).
• A control of the sugar loading in the labile carbon pool on NUE is proposed in r5976
• Following r5976 the transfer from carbon between the labile and reserve pool was revised in r6010. This may be the most disruptive change related to this ticket.
• r6010 has the sugar loading as a function of the labile and reserve pool. This helps to stabilize the approach.
• r6010 externalized the parameter root_reserve. At the same time some minor inconsistency were fixed (sometimes the parameter was used (= 1), sometimes a hard coded value (=0.3) was used.
• r6010 also fixed some bugs in turnover but most of those are likely limited to CN-CAN.
• The above revisions have been implemeted and tested in ORCHIDEE-CN-CAN. They still need to reviewed and transferred into the trunk.

• Limiting the labile carbon exposed problems with gtemp in stomate_growth_fun_all (see #561). The current solution uses the entire labile pool at every time step. This seems acceptable but implies that we no longer decouple GPP and NPP as is the case in CN, DOFOCO and the current trunk. Strictly coupling the GPP and NPP goes back to an older modelling approach that assumed a strong coupling between GPP and NPP.

[aducharne]

Réunion ticket du 21/11/2019:

Ces problemes touchent toutes les PFTs. Une partie peut etre réglée par un patch en cours de test par Nicolas Vuichard, dont l'analyse doit etre approfondie avant d'envisager un committ.

Autres pistes :

• lien possible avec l'excès de bois, cf ticket #546
• peut-on exsuder une partie de ce carbone au niveau des racines

[nvuilsce]

A control of the sugar loading impacting on the Nitrogen use efficiency has been implmented in the trunk version (r6445), following developments done in CN-CAN (see r5976, r6010). This feature will replace the extra autotrophic respiration due to an excess of labile carbon.

Two adjustments have been done compared to the implementation in CN-CAN:

• this feature can only negatively impact on NUE (ie a reduction of NUE). Thus the default parameter setting for sugar_max is now 1.0. It is set to 1.1 in CN-CAN.
• the functionality is based on the ratio between the labile+reserve pools and targeted values of these 2 pools. To avoid abrupt changes, we compute a weekly-smoothed value of this ratio. Then, based on this ratio, we compute a function by applying only a low and high thresholds to this ratio (resp. 0.3 and 1.0). In the trunk, instead of computing a weekly-smoothed value of the ratio, we directly compute weekly-smoothed value of the function. This should potentially avoid to keep a long-term legacy of periods where labile+reserve pools are excessively low compared to the targeted values.

Preliminary tests have been done with revision 6342 of the trunk.

[jgipsl]

Said by SL during ORCH meeting today: this ticket should be closed by NVuich or SL.