The Role of Soil Organic Matter and Manures in Sustainable Nutrient Cycling - Sustainable Management of Soil Organic Matter - page 327

Fig. 4.14.4.

15 N ratios in profiles of a Typic Aquiturbel representing the forest tundra,
a Typic Cryaquept representing the northern taiga, and an Oxaquic Dystrocryept representing the
central taiga.

δ

13 C and δ

considered. Isotopic discrimination is largest in the southern soils,
indicating that SOM of these soils is the most processed. However, the
strong discrimination observed in mineral surface horizons of the southern
soils suggests anaerobic processes, i.e. methanogenesis and denitrification.
Both processes result in a pronounced enrichment of the heavier isotope in
soil. Reasons for the possibly lower potential of CH 4 and N 2 O formation
under forest tundra are less available primary C sources, the longer period
when the soils are frozen and the lower soil temperature. The low tempera-
ture in the sub-soils close to the permafrost table may also account for the
decreasing

15 N values in the sub-soils. Yet, we can only speculate about
the reason for this observation. It could be due to incorporation of light
NH 4 into sub-soil SOM, enrichment of light NO 3 and N 2 O in the sub-soil,
or a decoupling of the nitrogen cycle in the sub-soil from that in the surface
soil.

δ

In conclusion, this study provides indications that watershed soils of
the forest tundra ecotone may be able to store more SOM if the belts of
vegetation shift northwards, but emissions of greenhouse gases may also
increase.

References

Bockheim, J.G., Ping, C.L., Moore, J.P. and Kimble, J.M. (1994) Gelisols: a new
proposed order for permafrost-affected soils. In: Kimble, J.M. and Ahrens, R.
(eds) Proceedings of the Meeting on Classification, Correlation, and Management
of Permafrost-affected Soils , July 18-30, 1993. Alaska, USA and Yukon and
Northwest Territories, Canada. USDA-SCS, Washington, DC, pp. 25-45.
Glaser, B., Haumaier, L., Guggenberger, G. and Zech, W. (1998). Black carbon in
soils: the use of benzenecarboxylic acids as specific markers. Organic Geochemis-
try 29, 811-819.