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 CO 2-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 CO 2-sequestration occurs concurrently with lowest soil nitrate (NO 3 −) concentrations, despite considerable N-loading. Not until drastic N-supply occurs, does the CO 2-sink successively breakdown, and nitrate concentrations increase, leading to NO 3 −-leaching. Within-soil CO 2-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.

Exogenous Nitrogen Addition Reduced the Temperature Sensitivity of Microbial Respiration without Altering the Microbial Community Composition

“…Such decreases could reduce nitrification rates, as previous studies have suggested that these two PLFAs are dominant fatty acids in N-oxidizing bacteria such as Nitrosomonas and Nitrobacter ( Petersen et al, 2004 ; Börjesson et al, 2011 ). Consequently, soil CO 2 emissions may increase due to the reduced within-soil CO 2 uptake ( Fleischer and Bouse, 2008 ; Fleischer, 2012 ), which is partially supported by the observation that nitrate additions consistently induced higher soil CO 2 emissions. This result implies that the decrease in the ammonium/nitrate ratio of atmospheric N deposition ( Liu et al, 2013 ) will tend to cause higher soil CO 2 emissions, which increases risk of further accelerating warming by inducing greater positive feedback.…”

“…Ammonium is the substrate for microbial nitrification, an N transformation process that could potentially enhance the within-soil CO 2 uptake ( Fleischer and Bouse, 2008 ). In contrast, nitrate may retard the nitrification process due to it being the product of nitrification, and could therefore increase soil CO 2 emissions in accordance with the Le Chatelier principle ( Fleischer and Bouse, 2008 ; Fleischer, 2012 ). In our study, several PLFAs showed consistent trends in response to N additions, e.g., compared with the control and ammonium addition treatments, nitrate addition reduced the relative abundance of 16:1w7c and 18:1w7c.…”

Responses of soil greenhouse gas emissions to land use conversion and reversion—A global meta‐analysis

“…The results of RFR identified that NH 4 + , WFPS, and soil clay with the importance of 0.249, 0.092, and 0.088, respectively, which were the relatively important driving factors for CO 2 emission response under land use conversion (Figure 6a). Previous study indicated that the increasing of added NH 4 + improved nitrification and reduced CO 2 emission until reaching the minimum value, and the further NH 4 + addition inhibited nitrification process gradually and resulted in the increase of CO 2 release (Fleischer & Bouse, 2008). Thus, the NH 4 + addition during the land use conversion would make the response fluctuation of CO 2 .…”

Dark oxidation of water in soils

“…Previous studies indicated that a part of CO 2 in the soil atmosphere was allocated into an internal soil CO 2 sink in different types of soils (Fleischer and Bouse, 2008;Fleischer, 2012). The process occurred in darkness, that is, photosynthesis could not explain this within-soil reduction of CO 2 .…”