THE GLOBAL CARBON-CYCLE - A VIEWPOINT ON THE MISSING SINK

Atmospheric carbon budgets that ignore the possibility of terrestrial ecosystem responses to global atmospheric change do not balance; there is a 'missing sink' of about 0.4 - 4 Gt C yr(-1). This paper argues a case that mechanistically it is well within the bounds of possibility that increasing carbon storage in vegetation and soils in response to the globally increasing CO2 concentration, temperature and nitrogen d eposition can account for the missing C sink. Global warming condition s considered alone would be unlikely to cause most ecosystems to emit CO2, because the N mineralised by any enhanced soil organic matter dec omposition would be largely taken up by plants and reconverted into or ganic matter having a much higher C:N ratio than that in the soil. Mod els of the global terrestrial C cycle indicate that an extra 0.5 - 4 G t C yr(-1) could well be being stored in soils and vegetation today in response to the CO2 fertilising effect, having regard for the interac tions with growth restricting water, light and nitrogen levels. To obt ain direct proof as to whether that this is happening or not is a majo r challenge.