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Aims The morphological traits of fine roots change with forest succession and soil weathering. However, low tree species diversity in boreal forests may limit plastic responses of the roots to soil nutrient loss. We tested whether pine trees (Pinus sylvestris L.) have root plasticity to change fine root allocation to deeper soil horizons in response to varying degree of podzolization. Methods We compared root biomass in two sand dune chronosequences (aluminium (Al)/iron (Fe) oxide-poor coarse-textured sand vs. oxide-rich fine-textured sand) in Estonia. Results We found that faster podzolization in coarse-textured soil promotes migration of Al/Fe oxides and phosphorus (P) into deeper horizons and reshapes the depth distribution of fine root biomass. A decrease in P availability in the coarse-textured soil profile increases fine root biomass and length in both the organic and mineral horizons. In the fine-textured old soil, fine root distribution increases in the mineral soil (especially, spodic horizon) rich in oxide-bonded P.Conclusion Pine roots have two plasticities in low-diversity boreal forests – changing root morphological traits and changing depth distribution of root biomass, depending on the abundance of Al and Fe oxides and the depth distribution and dominant form of P.

Supplemental material, Appendix_A for Extending the applicability of the REVEALS model for pollen-based vegetation reconstructions to coastal lagoons by Julien Azuara, Florence Mazier, Vincent Lebreton, Shinya Sugita, Nicolas Viovy and Nathalie Combourieu-Nebout in The Holocene