Summary:

N-Limitation of Decomposition Fluxes

This section discusses how the availability of mineral nitrogen can limit decomposition rates in ecosystems. The key points are:

Potential Decomposition Fluxes
- The potential carbon flux out of an "upstream" pool (u) is given by the product of the pool size (CS_u) and the decay rate constant (k_u).
- The potential mineral nitrogen flux associated with this decomposition can be a source or sink, depending on the C:N ratios of the upstream and downstream pools, as well as the respiration fraction.

Equations for Potential Fluxes
- Equations are provided to calculate the potential carbon fluxes from different carbon pools (Lit1, Lit2, Lit3, SOM1, SOM2, SOM3, SOM4) in the CLM-CN model.
- Corresponding equations are given for the potential mineral nitrogen fluxes associated with these decomposition steps.

Mineralization vs. Immobilization
- Mineralization fluxes (release of new mineral nitrogen) are allowed to proceed at their potential rates without modification.
- Immobilization fluxes (uptake of mineral nitrogen) are subject to rate limitation based on mineral nitrogen availability, total immobilization demand, and total demand for soil mineral nitrogen to support plant growth.

Overall, the section describes the mathematical framework for calculating potential decomposition fluxes and how nitrogen availability can limit these fluxes in ecosystem models.