Climatic role of terrestrial ecosystem under elevated CO 2 : a bottom‐up greenhouse gases budget

The net balance of greenhouse gas ( GHG ) exchanges between terrestrial ecosystems and the atmosphere under elevated atmospheric carbon dioxide ( CO 2 ) remains poorly understood. Here, we synthesise 1655 measurements from 169 published studies to assess GHG s budget of terrestrial ecosystems under elevated CO 2 . We show that elevated CO 2 significantly stimulates plant C pool ( NPP ) by 20%, soil CO 2 fluxes by 24%, and methane ( CH 4 ) fluxes by 34% from rice paddies and by 12% from natural wetlands, while it slightly decreases CH 4 uptake of upland soils by 3.8%. Elevated CO 2 causes insignificant increases in soil nitrous oxide (N 2 O) fluxes (4.6%), soil organic C (4.3%) and N (3.6%) pools. The elevated CO 2 ‐induced increase in GHG emissions may decline with CO 2 enrichment levels. An elevated CO 2 ‐induced rise in soil CH 4 and N 2 O emissions (2.76 Pg CO 2 ‐equivalent year −1 ) could negate soil C enrichment (2.42 Pg CO 2 year −1 ) or reduce mitigation potential of terrestrial net ecosystem production by as much as 69% ( NEP , 3.99 Pg CO 2 year −1 ) under elevated CO 2 . Our analysis highlights that the capacity of terrestrial ecosystems to act as a sink to slow climate warming under elevated CO 2 might have been largely offset by its induced increases in soil GHG s source strength.