Summary of "Aerenchyma Transport":

Aerenchyma Transport in the Community Land Model (CLM)

Gaseous Diffusion
- Aerenchyma transport is modeled in CLM as gaseous diffusion driven by a concentration gradient between the soil layer and the atmosphere.
- Vertical advection with the transpiration stream can also contribute to the transport.
- The diffusive transport is represented by an equation that considers factors like gas diffusion coefficient, gas concentration, root length, porosity, aerenchyma area, and aerodynamic resistance.

Aerenchyma Porosity
- Baseline aerenchyma porosity values are set to 0.3 for grass and crop plant functional types (PFTs), and 0.1 for tree and shrub PFTs.
- The specific aerenchyma area is calculated based on annual net primary production, belowground fraction of NPP, and aerenchyma radius.

Methane Emission
- CLM simulates the direct emission of methane from leaves to the atmosphere via transpiration of dissolved methane.
- This flux is calculated using the simulated soil water methane concentration and the predicted transpiration for each PFT, assuming no methane oxidation inside the plant tissue.