title: A review of nitrogen enrichment effects on three biogenic GHGs: the CO2 sink may be largely offset by stimulated N2O and CH4 emission.
abstract: Anthropogenic nitrogen (N) enrichment of ecosystems, mainly from fuel combustion and fertilizer application, alters biogeochemical cycling of ecosystems in a way that leads to altered flux of biogenic greenhouse gases (GHGs). Our meta-analysis of 313 observations across 109 studies evaluated the effect of N addition on the flux of three major GHGs: CO(2), CH(4) and N(2)O. The objective was to quantitatively synthesize data from agricultural and non-agricultural terrestrial ecosystems across the globe and examine whether factors, such as ecosystem type, N addition level and chemical form of N addition influence the direction and magnitude of GHG fluxes. Results indicate that N addition increased ecosystem carbon content of forests by 6%, marginally increased soil organic carbon of agricultural systems by 2%, but had no significant effect on net ecosystem CO(2) exchange for non-forest natural ecosystems. Across all ecosystems, N addition increased CH(4) emission by 97%, reduced CH(4) uptake by 38% and increased N(2)O emission by 216%. The net effect of N on the global GHG budget is calculated and this topic is reviewed. Most often N addition is considered to increase forest C sequestration without consideration of N stimulation of GHG production in other ecosystems. However, our study indicated that although N addition increased the global terrestrial C sink, the CO(2) reduction could be largely offset (53-76%) by N stimulation of global CH(4) and N(2)O emission from multiple ecosystems.
authors.affiliation: Environmental Media Assessment Group - MD B243-01, National Center for Environmental Assessment, Office of Research and Development, U.S. EPA, Research Triangle Park, NC 27711, USA. lingliliu@hotmail.com
authors.forename: Lingli
authors.initials: L
authors.lastname: Liu
authors.forename: Tara L
authors.initials: TL
authors.lastname: Greaver
mesh_terms: D000393:Air Pollutants / Q000032:analysis* / Q000737:chemistry; D002245:Carbon Dioxide / Q000032:analysis* / Q000737:chemistry; D017753:Ecosystem; D004784:Environmental Monitoring; D017752:Greenhouse Effect; D008697:Methane / Q000032:analysis* / Q000737:chemistry; D009584:Nitrogen / Q000737:chemistry*; D009585:Nitrogen Dioxide / Q000032:analysis* / Q000737:chemistry
chemical_list: D000393:Air Pollutants; D002245:Carbon Dioxide; D009584:Nitrogen; D008697:Methane; D009585:Nitrogen Dioxide