## 2.10.1. Model inputs and parameter estimations[¶](#model-inputs-and-parameter-estimations "Permalink to this headline")
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The LUNA model includes the following four unitless parameters:

*   \\(J\_{maxb0}\\) , which specifies the baseline proportion of nitrogen allocated for electron transport;
    
*   \\(J\_{maxb1}\\) , which determines response of electron transport rate to light availability;
    
*   \\(t\_{c,j0}\\) , which defines the baseline ratio of Rubisco-limited rate to light-limited rate;
    
*   \\(H\\) , which determines the response of electron transport rate to relative humidity.
    

The above four parameters are estimated by fitting the LUNA model to a global compilation of >800 obervations located at different biomes, canopy locations, and time of the year from 1993-2013 (Ali et al. 2015). The model inputs are area-based leaf nitrogen content, leaf mass per unit leaf area and the driving environmental conditions (average of past 10 days) including temperature, CO 2 concentrations, daily mean and maximum radiation, relative humidity and day length. The estimated values in CLM5 for the listed parameters are 0.0311, 0.17, 0.8054, and 6.0999, repectively. In LUNA V1.0, the estimated parameter values are for C3 natural vegetations. In view that potentially large differences in photosythetic capacity could exist between crops and natural vegetations due to human selection and genetic modifications, in CLM5, the LUNA model are used only for C3 natural vegetations. The photosynthetic capacity for crops and C4 plants are thus still kept the same as CLM4.5. Namely, it is estimated based on the leaf nitrogen content, fixed RUBISCO allocations for \\(V\_{c\\max 25}\\) and an adjusting factor to account for the impact of day length. In CLM5, the model simulates both sun-lit and shaded leaves; however, because the sun-lit and shaded leaves can changes through the day based on the sun angles, we do not differentiate the photosynthetic capacity difference for sun-lit or shaded leaves.

