Variable microbial stoichiometry

[wwieder]

The first implementation of MIMICS-cn uses fixed stoichoimetry for MICr and MICK (6 & 10, respectively), resulting in a weak / absent latitudinal gradient that is inconsistent with observations from Xu et al. 2013.

Alternative strategies would be to have microbial C:N be a function of litter quality (see Liu et al. 2019, inorganic N availability (as in C:N pools w/in DAYCENT), or others?

[wwieder]

@melanniehartman I tried adding this feature with these code modifications.
the model seems to be running, do you mind taking a look at the code differences here?
e4ea7f3

[melanniehartman]

Hi Will, Your updates look good to me! I was just wondering about the modification to microbial C:N that is dependent on litter. *mimics_cycle_CN.f90 lines 1595-1595:* So the microbe C:N increases with the metabolic litter fraction? I had been thinking it would increase when microbes consume more structural (high C:N) litter (when fmet decreases). I see you added a new parameter, mimicsbiome%cnModDenom. What kind of value does it have? mimicsbiome%CN_r(npt) = mimicsbiome%CNr * SQRT(mimicsbiome%fmet(npt)/mimicsbiome%cnModDenom) mimicsbiome%CN_k(npt) = mimicsbiome%CNk * SQRT(mimicsbiome%fmet(npt)/mimicsbiome%cnModDenom)

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On Thu, Nov 19, 2020 at 11:17 AM will wieder ***@***.***> wrote: @melanniehartman <https://github.com/melanniehartman> I tried adding this feature with these code modifications. the model seems to be running, do you mind taking a look at the code differences here? e4ea7f3 <e4ea7f3> — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#41 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AJHX3JYKZYHBUK2KRCUHGPTSQVOM5ANCNFSM4T3STZJQ> .

[wwieder]

oh, you're @melanniehartman right I did this the wrong way, leading to increases in micCN with higher quality letter, which was not intended. See fig on the left (with variable micCN, vs. the baseline case)

[melanniehartman]

I imagine you'll just use 1-fmet instead? Looks like the modification makes a big difference. It will be interesting to see the larger impact.

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On Thu, Nov 19, 2020 at 3:16 PM will wieder ***@***.***> wrote: oh, you're @melanniehartman <https://github.com/melanniehartman> right I did this the wrong way, leading to increases in micCN with higher quality letter, which was not intended. See fig on the left (with variable micCN, vs. the baseline case) [image: image] <https://user-images.githubusercontent.com/8031012/99730748-321bee00-2a7a-11eb-8f8c-b4850718a382.png> — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#41 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AJHX3J5Q4JRSSCBKG27CD4DSQWKNBANCNFSM4T3STZJQ> .

[wwieder]

Yep, I just flipped the function result on the left are with the modified C:N, the default is on right.

[wwieder]

target microbial C:N switches too quickly, causing crazy behavior. @melanniehartman what would cause fMET to change so much at a single time? These results are from a single grid cell exhibiting this behavior of the 20th century.

[wwieder]

I think this has something to do with increases slight changes in inorganic N that increase wood decay, resulting in big shifts fMET, which feedback to further increase N mineralization rates. I've tried turning off N limitation of wood decay in casa_inout for MIMICS to test this. then we can discuss...

Here's a figure of global stocks during spinup shoting the accumulation of CWD (as well as wiggles in stocks)

[wwieder]

This whole section of code could be removed if we want wood decay to be unaffected by N availability:
https://github.com/wwieder/biogeochem_testbed_1.1/blob/2352ec4e6307a4d518d834ce5890727bf192cd91/SOURCE_CODE/casa_inout.f90#L1624
@melanniehartman I wonder if the call to casa_nuptake below this line is now incorrect, as we're not applying N limitation to cwd decomposition

[wwieder]

Also needed to but min value on Lignin:N ratios to keep fmet from being too low (or negative) in forests with higher CWDc flux. Currently capped at 40 and ~0.25, respectively.
https://github.com/wwieder/biogeochem_testbed_1.1/blob/2352ec4e6307a4d518d834ce5890727bf192cd91/SOURCE_CODE/mimics_cycle_CN.f90#L652
Updated in mimics_delplant above for consistency too, but needs to be done in mimics_cycle.f90 too...

[wwieder]

Wood dynamics look better with revisions mentioned above and a smoother accumulation of steadystate C pools (here for the last 10k years of a 20k spinup.