Pool of Lignin Phenols in Soils of Secondary Forests

The purpose of this study is to characterize the pool of lignin phenols in soils of two contrasting secondary forest ecosystems—boreal and tropical—with different tree species and to assess the rate of biochemical transformation of difficult-to-degrade compounds of lignocelluloses nature in them. A detailed and comparative description of the biochemistry of lignin in soils in experiments on artificial afforestation in Krasnoyarsk krai of Russia (Greyzemic Phaeozems (Albic)) and in the Amazon Region, Brazil (Xanthic Ferralsol) is presented. Determination of lignin in soils involved alkaline oxidation with copper oxide at 170°C under pressure in a nitrogen atmosphere. Lignin phenols (vanillin, syringyl, and cinnamyl) were separated, using gas chromatography. It has been shown that lignin mineralization is rapid in soils of both boreal and tropical secondary forests contrary to soils of natural zonal ecosystems. A significant enrichment of lignin with metabolic carbon is a characteristic feature of this process. Low content, high oxidation rate, and a high degree of transformation of lignin are typical for soils of all the studied secondary forests, for tropical ones in particular, which reduces their potential as carbon sink reservoirs versus taiga soils.