The Role of Soil Organic Matter and Manures in Sustainable Nutrient Cycling - Sustainable Management of Soil Organic Matter - page 325

Soil organic matter along the climatic gradient

Carbon stocks ranged from ~100 to ~275 Mg ha −1 m −1 soil depth and
peaked in soils of the northern taiga (Fig. 4.14.2). This is probably due to a
relatively high primary production with a concurrent strong hydromorphy
of the soils which restrains OM degradation. In particular in the northern
soils, sub-soil horizons contain the most C of the profiles which may be due
to slow SOM turnover in the deeper parts of the active layer. The C : N
ratios in the A horizons of the soils decrease from 21.7 in the central taiga to
19.7 in the northern taiga, to 14.5 in the forest tundra, suggesting a higher
contribution of microbial-derived organic matter in the northerly soils.
The yield of lignin-derived CuO oxidation products in SOM of the
mineral soil horizons decreased from south to north (Fig. 4.14.3). Concur-
rently, the side chain oxidation of the remnant lignin increased, being
indicative of a more advanced lignin degradation in the north. We suggest
that this is due to the lower root litter input that renews the SOM into
the mineral horizons of the northern soils (the root density in mineral soil
horizons was lower). In contrast, SOM of the northern soils appeared to be
richer in microbial (i.e. bacterial) cell wall residues as is indicated by the
amino sugar contents. This can be explained by the more unfavourable
conditions (stronger hydromorphy, lower soil temperature) for microbial
re-mineralization of the cell wall constituents. Pyrogenic C is a major C

Fig. 4.14.2. Carbon stocks in the soils of the forest tundra, northern taiga and central taiga.