fungal wood respiration

[rgknox]

Description:

This set of changes introduces a new heterotrophic respiration loss applied to coarse woody debris. This loss pathway is designed to mimic fungal wood decomposition, prior to entering the decomposition cascades in the host model. This is applied to the fragmented loss fluxes. A portion of the fragmented carbon loss from wood is sent to the hosts for further decomposition, and a portion is lost to the atmosphere now as this fungal respiration term.

This change was motivate through discussions and brainstorming by the NGEET nutrient: including Anthony Walker, Charlie Koven, Xiaojuan Yang, Matthew Craig, Daniela Yaffar, Mingjie Shi, myself and others.

New FATES parameter: fates_cwd_hrfrag_frac

This sets the fraction of carbon that is lost to fragmentation that ends up as fungal respiration flux. Note that the higher the value of this term, the lower the C/N and C/P ratio (i.e. higher nutrient concentration) of the fragmentation flux into the host.

Control of total fragmentation rate remains unchanged, and is still based on a maximum rate set by the parameters: fates_frag_maxdecomp

This parameter is most useful in nutrient limited simulations. Moreover, we have found that this parameter is important to keeping C/N ratios of the total litter pool at lower and reasonable levels.

Collaborators:

Conceptual design:
@walkeranthonyp, @ckoven, Xiaojuan Yang, @rgknox

Expectation of Answer Changes:

These changes should not impact C-only runs, aside from specific output variables related to litter composition. C-only dynamics should not be affected by this change.

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
• FATES-CLM6 Code Freeze: satellite phenology regression tests are b4b

If satellite phenology regressions are not b4b, please hold merge and notify the FATES development team.

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:

FATES baseline hash-tag:

Test Output:

[ckoven]

This looks awesome @rgknox, thanks! Everything here looks great to me. The only comment I have is that we should probably pass this information on the fungal respiration flux through a bc_out field to the host model, so that it can be added into the HR, NEE, and NBP history variables as well. Not sure if that should come with this PR or a separate one though.