Forest restoration approaches affect soil compositions of lignin, substituted fatty acids, and lignin degradation-associated genes.
The study of soil microorganisms and the composition of organic carbon is important for understanding the dynamics of soil organic carbon. The means by which forest restoration approaches might affect the soil composition of lignin, substituted fatty acids, and the lignin degradation genes, remain understudied. We hypothesized that the soils of naturally restored forests have more abundant and stable lignin, SFA, and lignin degradation genes than those of artificially restored plantations. We analyzed the compositions of lignin, SFA, and the lignin degradation genes in soils restored with natural secondary forests, native species plantations, and introduced species plantations. We found that the extractable lignin content, leaf-derived SFA, leaf- to root-derived SFA ratio, and lignin oxidation state were higher in natural secondary forests than in plantations. The abundances of genes involved in glyoxal oxidase, lignin peroxidase, and manganese peroxidase were higher in the soils of natural secondary forests than in those of the two plantation types. No significant differences in the above indices were found between soils of native and introduced plantations. Nutrients and lignin oxidation state, including tree richness, litter stock, available nitrogen, combined clay and silt content, syringyl-based lignin to vanillyl-based lignin ratio, syringic acid to syringaldehyde ratio, and SFA content significantly affected the composition of genes involved in lignin degradation. Nutrients and lignin oxidation state explained 41.9% of the variation in the composition of lignin degradation genes. The lower lignin oxidation state, higher nutrient availability, and higher aboveground inputs led to a higher abundance of lignin degradation genes in the soils of natural secondary forests than in those of the plantations. These results provide insight into the effects of forest restoration approaches on soil carbon sequestration.