Summary:

## Environmental Modifiers on Decomposition Rate

The base decomposition rates in the Community Land Model (CLM) are modified by several environmental factors on each time step:

1. Temperature Scalar (r_tsoil): Calculated using a Q10 approach, with Q10 = 1.5. This accounts for the effect of soil temperature on decomposition.

2. Moisture Scalar (r_water): Calculated based on soil water potential, using a relationship from Andrén and Paustian (1987). This accounts for the influence of soil moisture on decomposition.

3. Oxygen Scalar (r_oxygen): Enabled when the CH4 submodel is used, this limits decomposition when there is insufficient molecular oxygen for microbial demand.

4. Depth Scalar (r_depth): An exponential decrease in decomposition rate with depth, to account for processes like priming effects, microscale anoxia, and mineral/aggregate stabilization that are not explicitly resolved.

The combined decomposition rate scalar (r_total) is calculated as the product of these four environmental modifiers. This approach allows the model to capture the complex interactions between soil temperature, moisture, oxygen availability, and depth on the overall decomposition dynamics.