title: The greenhouse gas balance of European grasslands.
abstract: The greenhouse gas (GHG) balance of European grasslands (EU-28 plus Norway and Switzerland), including CO2 , CH4 and N2 O, is estimated using the new process-based biogeochemical model ORCHIDEE-GM over the period 1961-2010. The model includes the following: (1) a mechanistic representation of the spatial distribution of management practice; (2) management intensity, going from intensively to extensively managed; (3) gridded simulation of the carbon balance at ecosystem and farm scale; and (4) gridded simulation of N2 O and CH4 emissions by fertilized grassland soils and livestock. The external drivers of the model are changing animal numbers, nitrogen fertilization and deposition, land-use change, and variable CO2 and climate. The carbon balance of European grassland (NBP) is estimated to be a net sink of 15 ± 7 g C m(-2 ) year(-1) during 1961-2010, equivalent to a 50-year continental cumulative soil carbon sequestration of 1.0 ± 0.4 Pg C. At the farm scale, which includes both ecosystem CO2 fluxes and CO2 emissions from the digestion of harvested forage, the net C balance is roughly halved, down to a small sink, or nearly neutral flux of 8 g C m(-2 ) year(-1) . Adding CH4 and N2 O emissions to net ecosystem exchange to define the ecosystem-scale GHG balance, we found that grasslands remain a net GHG sink of 19 ± 10 g C-CO2 equiv. m(-2 ) year(-1) , because the CO2 sink offsets N2 O and grazing animal CH4 emissions. However, when considering the farm scale, the GHG balance (NGB) becomes a net GHG source of -50 g C-CO2 equiv. m(-2 ) year(-1) . ORCHIDEE-GM simulated an increase in European grassland NBP during the last five decades. This enhanced NBP reflects the combination of a positive trend of net primary production due to CO2 , climate and nitrogen fertilization and the diminishing requirement for grass forage due to the Europe-wide reduction in livestock numbers.
authors.affiliation: Laboratoire des Sciences du Climat et de l'Environnement, UMR8212, CEA-CNRS-UVSQ, 91191, Gif-sur-Yvette, France.|Sorbonne Universités (UPMC, Univ Paris 06)-CNRS-IRD-MNHN, LOCEAN/IPSL, 4 place Jussieu, 75005, Paris, France.
authors.forename: Jinfeng
authors.initials: J
authors.lastname: Chang
authors.affiliation: Laboratoire des Sciences du Climat et de l'Environnement, UMR8212, CEA-CNRS-UVSQ, 91191, Gif-sur-Yvette, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Ciais
authors.affiliation: Laboratoire des Sciences du Climat et de l'Environnement, UMR8212, CEA-CNRS-UVSQ, 91191, Gif-sur-Yvette, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Viovy
authors.affiliation: Laboratoire des Sciences du Climat et de l'Environnement, UMR8212, CEA-CNRS-UVSQ, 91191, Gif-sur-Yvette, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Vuichard
authors.affiliation: Sorbonne Universités (UPMC, Univ Paris 06)-CNRS-IRD-MNHN, LOCEAN/IPSL, 4 place Jussieu, 75005, Paris, France.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Sultan
authors.affiliation: INRA, Grassland Ecosystem Research Unit, UREP, 63100, Clermont-Ferrand, France.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Soussana
mesh_terms: D000397:Air Pollution / Q000032:analysis*; D057486:Carbon Cycle; D003247:Conservation of Natural Resources; D005060:Europe; D005740:Gases / Q000032:analysis; D065948:Grassland; D017752:Greenhouse Effect; D008954:Models, Biological; D008956:Models, Chemical; D012621:Seasons
chemical_list: D005740:Gases
keywords: European grassland; ORCHIDEE; grassland management; greenhouse gases balance; livestock