sum_of_clm_tech_note/CLM50_Tech_Note_FUN/2.18.7.-Calculation-of-N-uptake-streams-from-active-uptake-and-fixationcalculation-of-n-uptake-streams-from-active-uptake-and-fixation-Permalink-to-this-headline.sum.md

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Calculation of N Uptake Streams from Active Uptake and Fixation

1. Determining Carbon Uptake Fluxes:

   • Once the final C_nuptake is known, the fluxes of C to the individual pools can be calculated as:
     • C_nuptake,x = C_frac,x * C_nuptake
     • N_uptake,x = C_nuptake / N_cost

2. Handling Unmet Nitrogen Uptake:

   • If the active and non-mycorrhizal N uptake (NO3 or NH4) exceeds the available N, the unmet uptake is calculated:
     • N_unmet,no3 = N_active,no3 + N_nonmyc,no3 - N_avail,no3
     • N_unmet,nh4 = N_active,nh4 + N_nonmyc,nh4 - N_avail,nh4
   • The active and non-mycorrhizal uptake fluxes are then adjusted to account for the unmet uptake.

3. Updating Carbon Spent:

   • The carbon spent on active and non-mycorrhizal uptake is updated based on the new, lower N acquisition in each layer/pool.

4. Accounting for Total Carbon:

   • The total carbon accounted for in each soil layer is calculated as:
     • C_accounted,x,j = C_spent,j,x - (N_acquired,j,x * CN_plant * (1.0 + gr_frac))