Changes between Version 27 and Version 28 of DevelopmentActivities/MergeOCN/Vuichard

Timestamp:

2014-02-06T14:34:03+01:00 (10 years ago)

Author:

nvuilsce

Comment:

--

DevelopmentActivities/MergeOCN/Vuichard

@@ -75 +75 @@
  I wonder why it assumes 2 m3 per m2 of soil. The depth of the soil is 2 meter but it doesn't mean that all the column contains only water, there is also soil, no ? The question is : what is the volume that is considered for the concentration of NH4+ and NO3-. Is it a volume of soil or of solution ? If it is a volume of solution, I would suggest to multiply by a factor corresponding to the relative volume of water within the soil (like soilhum). Not done yet. 
 
-* '''Coefficient low_K_N_min'''. See eq. 8 of SM of Zaehle et al. (2010) and Table S1. In table S1, it is defined as the "Rate of N uptake not associated with Michaelis- Menten Kinetics" and the given value is 0.05 (-). It is mentioned also (unitless) but to my opinion it should have the same unit that 1/K_N_min or 1/N_min, so ((gN m-2)-1). So far, I cannot relate the value of low_K_N_min (0.05) to any reference, especially Kronzucker (1996). If I refer to Figure 4 of Kronzucker showing the NH4+ influx as a function of NH4+ concentration, the slope of the relationship could be used to define Vmax*low_K_N_min. For a concentration of NH4+ of 50 mmol, the influx equals 35 umol g-1 h-1. For a concentration of NH4+ of 20 mmol, the influx equals 17 umol g-1 h-1. So the slope can be written as 
- slope = 10-3 * (35 - 17) / (50 - 20) = 10-3 * 18 / 30 = 0.0006 g-1 h-1 
- and consequently low_K_N_min = slope / Vmax = 0.0006 / 3 = 0.0002 (umol)-1 
+* '''Coefficient low_K_N_min'''. See eq. 8 of SM of Zaehle et al. (2010) and Table S1. In table S1, it is defined as the "Rate of N uptake not associated with Michaelis- Menten Kinetics" and the given value is 0.05 (-). It is mentioned also (unitless) but to my opinion it should have the same unit that 1/K_N_min or 1/N_min, so ((gN m-2)-1). So far, I cannot relate the value of low_K_N_min (0.05) to any reference, especially Kronzucker (1996). If I refer to Figure 4 of Kronzucker showing the NH4+ influx as a function of NH4+ concentration, the slope of the relationship could be used to define Vmax*low_K_N_min. 
+ * For a concentration of NH4+ of 50 mmol, the influx equals 35 umol g-1 h-1. 
+ * For a concentration of NH4+ of 20 mmol, the influx equals 17 umol g-1 h-1. So the slope can be written as 
+ * slope = 10-3 * (35 - 17) / (50 - 20) = 10-3 * 18 / 30 = 0.0006 g-1 h-1 
+ and consequently 
+ * low_K_N_min = slope / Vmax = 0.0006 / 3 = 0.0002 (umol)-1 
+
  Using the Conversion factor from (umol per litter) to (gN m-2) conv_fac_concent = 14 * 1e3 * 1e-6 * 2, one should get 
  low_K_N_min = 0.0002 / ( 14 * 1e3 * 1e-6 * 2 ) = 0.007 ((gN m-2)-1)
- The value of 0.007 does not match with the one in OCN (0.05). This needs to be clarified
+ The value of 0.007 does not match with the one in OCN (0.05, (see [source:branches/orchidee-N/ORCHIDEE/src_stomate/stomate_soilcarbon.f90@19#L897 here])). This needs to be clarified
+
+ * '''N uptake by plants''' (2). In eq. 8 of SM of Zaehle et al. (2010) I think there is an error. It should not be (Nmin X KNmin) but (Nmin + KNmin). The source code of OCN is correct (see [source:branches/orchidee-N/ORCHIDEE/src_stomate/stomate_soilcarbon.f90@19#L897 here]).
 
 
 
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