MIMICS+ in FATES

[shelby147]

I am working on coupling MIMICS+ with CLM-FATES. This is part of the NorSink project, which aims to improve soil C modeling in Norway, but I want to plan for this to be globally applicable. MIMICS+ simulates soil C and N cycling by bacteria and fungi, including plant N acquisition from mycorrhizal fungi.

Betty (also here at UiO) has been working on coupling CLM with MIMICS+. In her work, mycorrhizal pools are represented on the PFT level of CLM.

The big question we should discuss first is, on what level do we simulate decomposition? (column, patch, cohort)? This has tradeoffs between computational reqs and our representation of ecological processes.

Another important question to consider is how will plants allocated C to mycorrhizae? In Betty's work, C allocation is a function of available C, N stress, and a maximum allocation fraction.

[rosiealice]

Thanks @shelby147! I am scheduling a meeting on this sometime next week or the wek after, but if anyone who isn't on my email thread for that has Thoughts on this matter, then just drop them here and I'll loop you in...

[wwieder]

Thanks for launching into this work @shelby147, I'm excited to see this moving forward.

FWIW the HLM are currently set up to handle soil processes at the column level. I appreciate this introduces challenges if plant C investment in fungal symbionts is supposed to result in N return. That said, we don't handle N competition very well at all right now, and it CLM-FATES is virtually un-tested.

I wonder if there's merit in digging into different formulations of N competition on CLM-FATES (maybe borrowing from RDA / ECA options in ELM-FATES) before diving too far into potential MIMICS+ developments?

[rosiealice]

Just noting for the sake of background (I know most of you know this backwards) but in FATES a 'patch' has different meanings depending on the mode we are using. In no-competition modes, each patch is occupied by only one PFT, with "site, land use, PFT, age" being the tiling hierarchy. And within each patch are cohorts of one PFT of differing sizes.

And in 'full FATES modes the hierarchy is "site, land use, age" and then PFTs compete within patches as cohorts of differing sizes.

So we need to think about how MIMICS+ might work in both these contexts. In an ideal world we'd like it to work in both types of simulation...

On a separate note, it's not completely clear to me that we'd want to directly link mycorrhizal functional type 1:1 with PFTs, because you can imagine that different aggregations of PFT in FATES may or may not break that assumption? Further one can also imagine that we might want mycorrhizae to build up after disturbance, and that age structured pools might be something we want to capture? And in other cases, we might also want to have some PFTs that can benefit from the mycorrhizae but don't contribute to them? Etc...

So obvs. we need to decide what is the set of ecological effects that we are most interested in capturing... and it's also likely that we will need a definition of Fungal Functional Types (FFTs. Please can we those?? 🤩) that is a bit flexible to handle different setups and questions.

On the N competition thing @wwieder, I agree that the CN competition in CLM-FATES hasn't been tested a lot, and so on some level we might be running-before-we-can-walk. Having said that, the ELM-FATES folk have been experimenting with the FATES nutrient model for a while now, and at least one of their model options is more or less the same as CLM's soil BGC (right @rgknox?) so maybe there is something to be gleaned from them to guide us here?

Also, when we add in MIMICS+ the N competition dynamics will all change quite a bit... But I take your point that there is also some (maybe parallel, as not all N uptake is via mycorrhizae) work to be done on ECA-type things? (https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1002/eap.1490 for reference on ECA)

While this MIMiCS+-FATES linkage is Shelby's project/job description, it's really for Shelby & Terje to decide their focus here. This thread here is all for guidance/context :)

[ckoven]

Hi all, and @shelby147 great that you are working on this! One thing to add, just for future-compatibility and extensibility, is that (as many here know) @glemieux is working to add the capability to have dynamic columns that correspond to patches (e.g. #1477 is the first step of this). So while currently we simulate decomposition at the site scale (i.e. averaged across all patches), once this is working and turned on, it would mean that the whole soil environment (including decomposition) is resolved separately for each patch (and thus you could have belowground successional effects). So this might influence how and where to put the mycorrhizae into the structure.

[rgknox]

One potential dynamic that is worth pointing out, is that the FATES CNP hypothesis is compatible with the idea that individual cohorts can produce exudates. The plants maintain stores of both C and N (and potentially P with ELM). We evaluate the ratios of these stores to optimize plant uptake of nutrients, like increase or decrease fine-root mass, or vmax. But it seems reasonable to extend this to spending on exudates as well. If N stores are low, the plant could ramp up exudatation (which would be a nice stabilizing mechanism for the plant-soil system).

[rosiealice]

Reminder of the meeting in an hour or so, and also I have made a google doc to track pros and con's of different approaches, here with a basic table for now (to be populated).