Summary:

## Decomposition in the Community Land Model (CLM)

The article describes the representation of decomposition of organic matter in the Community Land Model (CLM). Key points:

### Decomposition Modeling
- CLM allows the user to choose between two different decomposition submodels:
  1. The CLM-CN pool structure used in CLM4.0
  2. A second pool structure based on the CENTURY model, with slower decomposition rates
- The decomposition process is modeled as a cascade of transformations between different organic matter pools (coarse woody debris, litter, soil organic matter)
- The decomposition can be modeled either as a single vertical level or with multiple vertical soil layers

### Equations
- For the single-level model, the carbon balance equation accounts for inputs, transfers between pools, and decomposition losses
- For the multilevel model, the equation also includes vertical transport via diffusion and advection

### Figures
- Figure 2.21.1 shows a schematic of the decomposition model
- Figure 2.21.2 compares the pool structures, transitions, respired fractions, and turnover times for the two alternate decomposition submodels

In summary, the article describes the flexibility of the CLM to represent different conceptual models of soil organic matter decomposition, including both single-level and vertically-explicit treatments.