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.