A simple parameterization of nitrogen limitation on primary productivity for global vegetation models

International audienceNitrogen limitation of ecosystem productivity is ubiquitous, and it is thought that it has and will have a significant impact on net ecosystem productivity, and thus carbon sequestration, in the context of ongoing future increase of atmospheric CO2 concentration and climate change. However, many vegetation models do not represent nitrogen limitation, and might thus overestimate future terrestrial C sequestration. This work presents a simple parameterization of nitrogen limitation that can be easily implemented in vegetation models which do not yet include a complete nitrogen cycle. This parameterization is based on the ratio between heterotrophic respiration (considered a "proxy" of net mineralization rate) and net primary productivity of the ecosystem (considered a "proxy" of nitrogen demand). It is implemented in a global vegetation model and tested against site experiments of CO2 fertilization and soil warming. Furthermore, global simulations of past and future CO2 fertilization are carried out and compared to other model results and available estimates of global C sequestration. It is shown that when N limitation is taken into account using the simple parameterization presented here, the model reproduces fairly realistically the carbon dynamics observed under CO2 fertilization and soil warming