A review of nitrogen enrichment effects on three biogenic GHGs: the CO 2 sink may be largely offset by stimulated N 2 O and CH 4 emission

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.