ORCHIDEE-CN-P (former branch ORCHIDEE-CNP)

This page describes the phosphorus cycle in ORCHIDEE-CN-P. It is based on ORCHIDEE-CN, which was extended and corrected as described here: ​https://forge.ipsl.jussieu.fr/orchidee/wiki/Branches/MergeOCN/Goll as well as additional non-documented bugfixes to avoid negative pools due to machine precisions as well as bugs.

The phosphorus cycle is an adaptation of the the model described by ​http://www.biogeosciences.net/9/3547/2012/bg-9-3547-2012.html . Nonetheless, the complexity was substantially increased due to the more detailed representation of the C and N cycle in ORCHIDEE compared to JSBACH.

Schematic representation of the key processes represented in ORCHIDEE-CNP

2. Technical modification to the nitrogen code

I modified the code a bit to avoid problems and redundant code. More information here: ​https://forge.ipsl.jussieu.fr/orchidee/wiki/DevelopmentActivities/ORCHIDEE-CNP/TechnicalMods

3. Conceptual modifications to the nitrogen cycle

3.1 soil mineral N concentration in soil solution

Following Smith et al (2014), I introduced the use of the maximum water holding capacity of soils (max_var_eau) to approximate pore space which to derive the average soil mineral N concentration in solution. The use of the actual water volume can not be recommended as we this would lead to high N concentration in soil water when soil water is very low. As we do not account for the inhibition of replenishment of mineral N in the soil solution around roots when soil water is scarce.

3.2 soil mineral N dyanmics

Several modification of the original OCN (Zaehle & Friend, 2010) in ORCHIDEE-CN were kicked out and the original formulation are used again. See code for details. Still, the mineral N stocks are unrealistic high. One approach to solve this is to use the modification to OCN described in the SI of Zaehle et al. (2011) (​http://://www.nature.com/ngeo/journal/v4/n9/extref/ngeo1207-s1.pdf). The general problem is that several details were changed in the soil mineral N routine, which are not tested. And more modification are needed. The easiest way would be to use the OCN formulation and parameters. They are well tested, while the ORCHIDEE-CN modification are not tested.

3.3 Biological N2 fixation (BNF)

3.3.1 Modified Cleveland et al. (1999) scheme

We introduce a module which computes BNF as a function of NPP, tissue C:N, and tissue & N:P. This approach is based on Cleveland et al (1999), Thornton et al. (2007), and Goll et al. (2012). When using the analytical spinup the BNF must be read in from a file to speed up the spin up. The file should contain the reference BNF rates for the respective climatic conditions. Such files are currently missing, but should be generated as soon as the model is ready.

3.3.2 Biological N2 fixation (BNF) from Yingping

The Cleveland scheme is heavily criticized due to good reason. Yingping Wang will provide maps with annual rates of BNF computed based more or less on Wang et al. (2007) for the historical period. To do so, Yingping needs TRENDY style simulations with a calibrated model.After publication of his model, he will share the code with us & we can compute BNF dynamically in ORCHIDEE.

4. New input files

You can find information on the new input files needed for the P cycle here: ​https://forge.ipsl.jussieu.fr/orchidee/wiki/DevelopmentActivities/ORCHIDEE-CNP/newInput

5. unresolved Issues

There are still unresolved issue with the model. They are listed here: ​https://forge.ipsl.jussieu.fr/orchidee/wiki/DevelopmentActivities/ORCHIDEE-CNP/issues

6. Howto install, compile & run the model

You can find information on how to setup the simulations here: ​https://forge.ipsl.jussieu.fr/orchidee/wiki/DevelopmentActivities/ORCHIDEE-CNP/howtoUse