Nitrogen cycling drives a strong within-soil CO2-sink

Abstract

For about three decades, it has not been possible to completely balance global carbon emissions into known pools. A residual (or 'missing') sink remains. Here evidence is presented that part of soil respiration is allocated into an internal soil CO2-sink localized to the saprophytic subsystem (roots excluded). The process occurs in forest, agricultural and grassland soils and is favoured by high N-deposition. Chemoautotrophic nitrification has a key role, and the most efficient internal CO2-sequestration occurs concurrently with lowest soil nitrate (NO3-) concentrations, despite considerable N-loading. Not until drastic N-supply occurs, does the CO2-sink successively breakdown, and nitrate concentrations increase, leading to NO3--leaching. Within-soil CO2-uptake seems to be of the same magnitude as the missing carbon sink. It may be gradually enforced by the ongoing input of nitrogen to the biosphere. © 2008 The Author Journal compilation © 2008 Blackwell Munksgaard.