SOIL CARBON RESPONSE TO BIOCLIMATE CHANGES WITHIN THE SOUTHERN PART OF THE FOREST ZONE OF RUSSIA

The South Taiga subzone extends for more than 700 km from N to S of the European part of Russia, where biota changes according to the climate conditions (i.e., towards drier and warmer conditions in the S). Mixed coniferous forests are replaced by broad-leaved forests within this subzone. Accordingly soil cover changes from sod - podzolic soils to gray forest soils under natural vegetation.

To estimate vegetation influence on soil organic matter distribution and dynamics, three major South Taiga ecosystems: forest - dry meadow - arable land, have been compared at three locations: 125 km N, 45 and 125 km to the S of Moscow.

Unlike arable lands, forest and meadow ecosystems stimulate SOM accumulation. Along the transect grater organic carbon pools were found in the grasslands than forests or arable lands, though from North to South the difference became less. Regardless of the location, forest soils accumulated in the topsoil the highest amount of organic carbon, but unlike in meadow or arable soils it dramatically decreased down the soil profile.

Organic matter associated with small aggregates (< 0.250 mm) is known to be the most stable in the soil versus that one associated with large aggregates which more susceptible to transformations. There was a more pronounced difference in the ecosystem impact on aggregate formation at the northern boundary of South Taiga, where meadow vegetation developed more large macroaggregates. Soils at the southern boundary did not show that much difference between sites of different management, demonstrating higher soil aggregation in general.

The majority of organic matter in the topsoil of northern located soils was associated with the aggregates larger than 2 mm under all types of ecosystems studied. In the subsoil, the particle-sized fraction (<0.053mm) contained higher amount of organic C under both meadow and forest ecosystems, while the highest amount of OM in the arable soil was concentrated in the small macroaggregates. Soil to the south demonstrated different distribution of organic matter within the aggregates. Up to 30 cm depth, macroaggregates were the most enriched with carbon, and forest ecosystem showed the most intensive accumulation. Down the soil profile macroaggregates remain to be the major contributors to the organic carbon pool.