Abstract
The purpose of the study is to characterize the pool of lignin phenols in the soils of two contrasting secondary forest ecosystems – boreal and tropical – under different tree species and to assess the rate of biochemical transformation of difficult-to-degrade lignocellulosic compounds in them. A detailed and comparative description of the biochemistry of lignin in soils in experiments on artificial afforestation in the Krasnoyarsk region of Russia (Gray Phaozems Albic) and in the Amazon (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 in soils of secondary forests, both boreal and tropical, a rapid process of lignin mineralization is observed in comparison with soils of natural zonal ecosystems. A characteristic feature of the process is a significant enrichment of lignin with metabolic carbon. Low lignin content, a high degree of oxidation of biopolymers and a high degree of transformation are characteristic of the soils of all studied secondary forests and especially of tropical ones, which reduces the potential of the latter as carbon sink reservoirs compared to taiga soils.