Tree species mediated soil chemical changes in a Siberian artificial afforestation experiment

Natural and human-induced changes in the composition of boreal forests will likely alter soil properties, but predicting these effects requires a better understanding of how individual forest species alter soils. We show that 30 years of experimental afforestation in Siberia caused species-specific changes in soil chemical properties, including pH, DOC, DON, Na⁺, NH₄ ⁺, total C, C/N, Mn²⁺, and SO₄ ^2-. Some of these properties –- pH, total C, C/N, DOC, DON, Na⁺ –- also differed by soil depth, but we found no strong evidence for species-dependent effects on vertical differentiation of soil properties (i.e., no species × depth interaction). A number of soil properties –- NO₃ ^–, N, Al³⁺, Ca²⁺, Fe³⁺, K⁺, Mg²⁺ and Cl^– –- responded to neither species nor depth. The six studied species may be clustered into three groups based on their effects on the soil properties. Scots pine and spruce had the lowest pH, highest C/N ratio and intermediate C content in soil. The other two coniferous species, Arolla pine and larch, had the highest soil C contents, highest pH values, and intermediate C/N ratios. Finally, the two deciduous hardwood species, aspen and birch, had the lowest C/N ratio, intermediate pH values, and lowest C content. These tree-mediated soil chemical changes are important for their likely effects on soil microbiological activities, including C and N mineralization and the production and consumption of greenhouse gases.