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Increasing CO2 Increases C and N Contents in a Grassland Gley Soil in New Zealand
Ross, D.J., Tate. K.R., Newton, P.C.D., Wilde, R.H. and Clark, H.  2000.  Carbon and nitrogen pools and mineralization in a grassland gley soil under elevated carbon dioxide at a natural CO2 spring.  Global Change Biology 6: 779-790.

What was done
Soil samples were collected around a natural CO2 vent located near Northland, New Zealand, to determine the effects of elevated CO2 on soil carbon and nitrogen contents.  The soil at the site is considered to be a gley; and the overlying vegetation is typical of native grasslands in the area consisting of both C3 and C4 species.  Samples were grouped into atmospheric CO2 concentrations identified as low (440 to 460 ppm) and high (510 to 900 ppm) for analyses.

What was learned
Several decades of exposure to elevated atmospheric CO2 significantly increased soil organic carbon and total nitrogen contents by 24%, while microbial carbon and nitrogen contents increased by 116%.

What it means
As the air's CO2 content rises, it is likely that gley soils supporting grassland ecosystems will exhibit increasing concentrations of soil carbon and nitrogen, as well as heightened microbiological activity.  Indeed, the results of this study led the authors to conclude that "storage of C and N [in these gley soils] can increase under prolonged exposure to elevated CO2."  Moreover, they say that "increased storage of soil organic matter at such springs can occur, even when soil C concentrations are already high."  Thus, it is likely that in the future, as the air's CO2 content continues to rise, vegetated gley soils will sequester increasingly greater amounts of both carbon and nitrogen and exhibit enhanced biological activity both above- and below-ground.