## 2.9.1. Summary of CLM5.0 updates relative to the CLM4.5[¶](#summary-of-clm5-0-updates-relative-to-the-clm4-5 "Permalink to this headline")
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We describe here the complete photosynthesis and stomatal conductance parameterizations that appear in CLM5.0. Corresponding information for CLM4.5 appeared in the CLM4.5 Technical Note ([Oleson et al. 2013](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#olesonetal2013)).

CLM5 includes the following new changes to photosynthesis and stomatal conductance:

*   Default stomatal conductance calculation uses the Medlyn conductance model
    
*   \\(V\_{c,max}\\) and \\(J\_{max}\\) at 25 oC: are now prognostic, and predicted via optimality by the LUNA model (Chapter [2.10](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/Photosynthetic_Capacity/CLM50_Tech_Note_Photosynthetic_Capacity.html#rst-photosynthetic-capacity))
    
*   Leaf N concentration and the fraction of leaf N in Rubisco used to calculate \\(V\_{cmax25}\\) are determined by the LUNA model (Chapter [2.10](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/Photosynthetic_Capacity/CLM50_Tech_Note_Photosynthetic_Capacity.html#rst-photosynthetic-capacity))
    
*   Water stress is applied by the hydraulic conductance model (Chapter [2.11](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/Plant_Hydraulics/CLM50_Tech_Note_Plant_Hydraulics.html#rst-plant-hydraulics))
    

