Summary:

**Vertical Distribution and Transport of Decomposing C and N Pools**

The article discusses the additional terms needed to calculate the vertically-resolved soil C and N budget in the Community Land Model (CLM):

1. Initial Vertical Inputs:
   - Aboveground inputs (leaf, stem) use a single exponential distribution with a default e-folding depth of 0.1m.
   - Belowground inputs (root) are distributed according to rooting profiles based on the Jackson et al. (1996) exponential parameterization.

2. Vertical Mixing:
   - Achieved through an advection-diffusion equation to account for slow, solid- and adsorbed-phase transport due to bioturbation, cryoturbation, and erosion.
   - Faster aqueous-phase transport is not included in CLM, but has been developed as part of the CLM-BeTR suite of parameterizations.
   - The default value of the advection term is 0 cm/yr, resulting in purely diffusive transport.
   - Diffusive transport rates differ between permafrost and non-permafrost soils:
     - For permafrost soils, a parameterization based on Koven et al. (2009) is used, with a constant diffusivity in the active layer and a linear decrease to zero at a depth of 3m (default).
     - For non-permafrost soils, the default diffusivity is 1 cm2/yr.

In summary, the article outlines the methods used in CLM to account for the initial vertical distribution of C and N inputs and the subsequent vertical transport of these decomposing pools through diffusive processes, with differences in the parameterization for permafrost and non-permafrost soils.