Contribution of Belowground Plant Residues to the Soil Carbon Pool in Forest Ecosystems of Middle and Southern Siberia

The contribution of belowground plant residues to soil carbon stock is estimated and the main factors potentially influencing the stock of root detritus are analyzed in 67 test plots situated in different natural-climatic zones of the Krasnoyarsk region and mountain forests of the western and eastern Cisbaikalia (Irkutsk oblast and Republic of Buryatia). The studies involve both the undisturbed old-growth forests and the forest ecosystems affected by clear cutting, wildfires, and aerotechnogenic pollution. The carbon stock in root residues is comparable to that in the forest litter and is even 1.3–1.9-fold larger in some cases, accounting for 3.6–167% of the carbon stock in soil humus. This stock and its contribution to the soil carbon pool of organic matter depend on the forest-forming species, soil type, and natural- climatic zone and can significantly increase as a result of impacts that disturb the aboveground vegetation and the pool of plant residues on soil surface. The underestimation of this component when assessing the forest ecosystem carbon budgets can lead to the underestimation of total soil carbon stock by 5–32% in undisturbed forest ecosystems and up to 40% after various disturbances.