Stem diffusion sub-model

[rgknox]

At the NGEE-Tropics all hands meeting, Kolby Jardine kicked off a discussion about stem respiration. The NGEE tropics project has dendrometer measurements and CO2 effflux measurments on the stem surface. Estimating stem respiration is typically tricky because the co2 diffuses through the tissues, gets dissolved and transported in the xylem water. But I think we could really dial in on better stem respiration parameterizations and model hypothesese if we could predict surface co2 fluxes and compare to data.

There are various ways we could go about this.

There could be a forward model, where we simply predict stem efflux. These model predictions combined with sapfllow predictions would help us run calibration or sensitivity analysis on stem respiration. I suppose there could be inverse models too, where we drive the submodule with estimated efflux and sapflow and generate respiration rates or some other co2 metricc (such as internal concentrations), but this would be something that stands alone.

Other groups have done some really interesting modeling work on this subject. "TreSpire" does various cool things: https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.16174 Along with estimation of growth and maintenance respiration, hydraulics (stuff fates does), it does have a diffusion and transport submodule.