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**Free Retranslocation of Leaf Nitrogen**

- Some nitrogen in the leaf pool is removed without requiring carbon expenditure, referred to as "free" nitrogen retranslocation.
- The free nitrogen retranslocation amount (`N_retrans,free`) is calculated as the maximum of (falling leaf nitrogen - (falling leaf carbon / minimum litter C:N ratio)), or 0.
- The minimum litter C:N ratio is currently set to 1.5 times the target C:N ratio.
- The new falling leaf nitrogen (`N_fallingleaf`) is then determined by subtracting the free nitrogen retranslocation amount from the original falling leaf nitrogen.
- The new litter C:N ratio (`CN_fallingleaf`) is calculated as the falling leaf carbon divided by the new falling leaf nitrogen.

The summary covers the key points about the calculation of free nitrogen retranslocation and the resulting changes to falling leaf nitrogen and litter C:N ratio.