PR for dynamic L2FR

[sharma-bharat]

Vegetation decline in CNP spinups: Is resetting of L2FR value after senescence a probable reason?

Description:

We see that the GPP, NPP, and LAI were declining rapidly during the AD Spinups during the RD and ECA runs both for evergreen needleleaf and cold-deciduous plant functional type but not for Carbon only runs (see Fig 1).

Increasing the initial period of supplemental N supported vegetation productivity but the decline in productivity happens when supplemental N is stopped.

Partial improvement was seen by commenting the call to dynamic L2FR for initial few decades. We see an increase in vegetation productivity but it was low. Commenting the call to dynamic L2FR throughout the AD spinup lead to increase in GPP but it was still much lower than expected (Fig 2).

We think that Fineroot biomass (FR) is dropping to near zero during the winter in the CNP simulations, especially in deciduous PFT when leaf-off is triggered (Fig 3). Near-zero winter FR might be preventing uptake of available N during periods of no leaves (or close enough). The big increase in FR each year will add a significant amount of real N demand (i.e. what's required for growth), contributing to the rapid depletion of the store.

We also noticed that the L2FR was resetting to default parameter L2FR after every senescence event. Thus, L2FR value of previous timestep was not used in resource allocation (as intended by subroutine CNPAdjustFrootTargets) in following timestep.

In summary,

• L2FR in each cohort's data structure is initialized with the value from the parameter file, the biomass targets in the CNP allocation routine are initially set here, before a first round of growth happens in CNPStatureGrowth, which happens before dynamic l2fr and target FR biomass is updated in another later second round of growth in CNPAllocateRemainder.

• L2FR is reset after every senescence event.

• Solution (results in Fig 4):

  • turning the dynamic L2FR off during the supplemental N period by conditional call to CNPAdjustFRootTargets on this line (see Code 1 below).

  • Change how l2fr is read in physiology code from this to Code 2 below.
    Code 1:

call get_curr_date(yr, mon, day, sec)                                       
if (spinup_state == 1 .and. yr .gt. nyears_ad_carbon_only) then             
    call this%CNPAdjustFRootTargets(target_c,target_dcdd)                   
else if (spinup_state /= 1) then                                                                                                                                                                                   
    call this%CNPAdjustFRootTargets(target_c,target_dcdd)                   
end if 

Code 2:

l2fr = currentCohort%l2fr

Figures

Fig 1: GPP, NPP, and AR in ad spins for cold deciduousPFT during Carbon only (top) and RD run (bottom). Similar plots are for needleleaf evergreen PFT.

Fig 2: GPP, NPP, AR in ad spins for cold-deciduous PFT during RD Run with dynamic L2FR (default) and without dynamic L2FR.

Fig 3: Leaf, Fineroot, and Store Carbon during the first 30 years of ad spinups for Carbon only (top), RD (middle), and ECA (bottom) runs for cold-deciduous PFT.

Fig 4: GPP, NPP, and AR in ad spins for RD using cold deciduous PFT (top) and needleleaf evergreen PFT (bottom). Similar plots are for ECA.

Collaborators:

Anthony Walker, ORNL (@walkeranthonyp)

Expectation of Answer Changes:

Checklist

If this is your first time contributing, please read the CONTRIBUTING document.

All checklist items must be checked to enable merging this pull request:

Contributor

• The in-code documentation has been updated with descriptive comments
• The documentation has been assessed to determine if updates are necessary

Integrator

• FATES PASS/FAIL regression tests were run
• Evaluation of test results for answer changes was performed and results provided

Documentation

• Technical Note update:
• User's Guide update:

Test Results:

CTSM (or) E3SM (specify which) test hash-tag:

CTSM (or) E3SM (specify which) baseline hash-tag: v2.1.0-13087-ge9afb7cb13

FATES baseline hash-tag: sci.1.68.2_api.31.0.0

Test Output: