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Effects of Nitrogen Deposition on Soil Carbon Storage
Hagedorn, F., Spinnler, D. and Siegwolf, R.  2003.  Increased N deposition retards mineralization of old soil organic matter.  Soil Biology & Biochemistry 35: 1683-1692.

Atmospheric CO2 enrichment typically enhances carbon sequestration in earth's soils by stimulating vegetative productivity and increasing the amount of plant litter that becomes incorporated into soil organic matter [see Carbon Sequestration (Soils) in our Subject Index].  Concomitant with the historical rise in the air's CO2 content, however, there has been an increase in anthropogenically-produced nitrogen deposition.  Hence, it behooves us to determine how this phenomenon also affects soil carbon storage, since extra carbon dioxide and oxides of nitrogen are sibling offspring of the Industrial Revolution.

What was done
The authors studied soil nitrogen (N) dynamics in model beech (Fagus sylvatica L.)-spruce (Picea abies Karst) ecosystems growing on an acidic loam and a calcareous sand in Switzerland within open-top chambers for a period of four years under low and high N deposition treatments (7 vs. 70 kg N ha-1 yr-1).

What was learned
Carbon inputs from trees into soils increased with increasing N, as would be expected.  In addition, there was a retarded mineralization of native soil organic matter (SOM) under the high N deposition treatment.  The authors also note that "N additions preserved old SOM in clay and silt separates, which comprise humified SOM."

What it means
The authors say their results demonstrate that the "preservation of old and humified SOM under elevated N deposition might be a process that could lead to an increased soil carbon storage in the long-term."  Together with atmospheric CO2 enrichment, there is thus a good potential for ever more carbon to be sequestered in the planet's soils as the burning of fossil fuels continues to increase.

Reviewed 7 January 2004