Quantification of the terrestrial CO2 fertilization effect

From CO2 experiments, we know that the range of observations on the CO2 fertilization effect follow the equation:

N:Myc + deltaCO2,

with N as nitrogen (N) status (N-limited or non N-limited), Myc as the type of mycorrhizal association (ectomycorrhizae -ECM- or arbuscular mycorrhizae -AM-), and deltaCO2 as the increase in atmospheric CO2 concentration.

For an increase in deltaCO2 from 400 to 650 ppm, the enhancement in plant total biomass for the different sub-classes is:

– AM-Nlimited: 0±5%
– ECM-Nlimited: 28±5%
– AM-nonNlimited:20±6%
– ECM-nonNlimited:33±4%

Therefore, we will use this framework to quantify the amount of carbon that plants will transform into biomass globally, by combining global estimates of N availability with global distribution of mycorrhizal plants. Unfortunately, both variables have not been successfully quantified at the global scale.
we have been mapping the distribution of mycorrhizal plants in the globe using David Read’s map of broad mycorrhizal plants distribution (Read 1991 Experientia), with a global vegetation cover map (GlobCover). The combination of both maps will indicate the geographical distribution of the above Myc-N sub-classes. The next step will be to estimate current plant productivity using model estimates. The CO2 fertilization effect at 650 ppm for a particular pixel will be the product of current productivity in that pixel and its corresponding percentage of biomass enhancement.