Summary:

## Canopy Scaling in LUNA Model

When LUNA (Land Use and Land Cover Change) is enabled, the following canopy parameters are scaled from sun leaves to shaded leaves:
- Vcmax25 (maximum carboxylation capacity)
- Jmax25 (maximum electron transport capacity)
- Tp25 (triose phosphate utilization)
- kp25 (permeability coefficient)
- Rd25 (dark respiration rate)

The scaling is done using the following equations:

(2.9.17)
- Vcmax25_sha = Vcmax25_sun * (iv,sha / iv,sun)
- Jmax25_sha = Jmax25_sun * (iv,sha / iv,sun)
- Tpsha = Tpsun * (iv,sha / iv,sun)

Where iv,sun and iv,sha are the leaf-to-canopy scaling coefficients for sunlit and shaded leaves, respectively, calculated using the two-stream radiation model (Equation 2.9.18).

The key parameters in the scaling coefficients are:
- kn,ext: extinction coefficient for nitrogen
- kb,ext: direct beam extinction coefficient
- fsun: fraction of sunlit leaves

When LUNA is disabled, the canopy scaling defaults to the mechanism used in CLM4.5.