Opened 14 months ago

Last modified 14 months ago

#766 new enhancement

Add carbon leaching

Reported by: luyssaert Owned by: somebody
Priority: major Milestone: Not scheduled yet
Component: Biogeochemical processes Version: trunc
Keywords: Cc:

Description (last modified by luyssaert)

GPP is the input of carbon. We can only allocate to tissue if we have enough N. If we don't, it goes to reserve pool. If we have too much in the reserves, then we reduce GPP with sugar loading. Higher LAIs will initially result in higher GPP but if the system lacks N to allocate the feedback through sugar loading may reduce the GPP on the long term. LAI and GPP are nicely coupled as long as sugar loading is not causing to much of a feedback, i.e. more than 75% (in other words GPP is reduced by less than 25% due to sugar loading).

in many places of the world and for all PFTs, the model needs a way to "burn off" the GPP that could not be allocated to biomass.

A high turnover of tissue would help in this respect. Earlier leaf longevity was checked and the current parameters are acceptable. In r7125 root longevity was decreased to more realistic values. When changing turnovers keep an eye on the calculation of c0_alloc as well as diameter (and height) growth.

Leaching of labile carbon to the soil (thought to be responsible for up to 20-30% of the NPP - textbook by Chapin 2012) comes to mind as another way to "burn off" excessive carbon. If we have a high GPP the same amount of C will go into tissue (limited by N), but rather than the excess going to the reserves (and decreasing GPP through the sugar loading) it would be leached into the soil organic matter. This could also increase the soil carbon, which is still desirable around r7113.

Initial literature study, sketches a much smaller role for carbon leaching. Philipps et al 2009 (doi:10.1093/treephys/tpp083) in Fig. 4 show a correlation between exudate and photosynthesis rates of Exudates = 0.068 * photosynthesis – 0.193. It seems that the relationship describes the exudate stock vs. photosynthesis rate  and  the exudate rate vs. photosynthesis rate. In the Lambers et al 1987 (in book: Growth, respiration, exudation and symbiotic association: The fate of carbon translocated to the roots) they give in table 1 numbers from 0.1mg/g of roots to 3.8mg/g of roots (but the measure are in dry mass and not in C). In Philipps et al 2011 (Ecology Letters, (2011) 14: 187–194) for the duke FACE site they wrote in table 1 values from 11.1 to 13.3 mg C/g root/year to total annual flux is from 23.3 to 34.8 gC/m2/yr with a NPP around 1500 gC/m2/yr for this site (Finzi et al., 2002) we have a ratio of indeed few percent. In the Pausch et al (DOI: 10.1111/gcb.13850) in fig. 9 they wrote that wrote that gross rhizodeposition is around 7-11% of the GPP but it is not clear if how much goes to mycorrhizae. In Farrar et al (Ecology, 84(4), 2003, pp. 827–837) there is the Fig. 2 where they wrote that 6% goes to mycorrhizae.

More important than the leaching itself would be to simulate the effects of leaching on nutrient uptake. The current model r7149 can respond to increased nitrogen through increasing the N-concentration in the tissue which would increase the GPP which in turn would increase the NPP. However, biomass/GPP (in this version of ORCHIDEE biomass is the same as NPP) will not change. Based on Vicca et al 2012 (Ecology letters) and Campiolli et al 2015 (Nature Geoscience) an increase in biomass/GPP ratio is expected if more nutrients are available.

Change History (2)

comment:1 Changed 14 months ago by luyssaert

  • Description modified (diff)
  • Milestone changed from ORCHIDEE 4.1 to Not scheduled yet

comment:2 Changed 14 months ago by luyssaert

  • Description modified (diff)
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