Multiple studies have shown that mixed-species forests often fulfill ecosystem services to a higher degree than mono-specific stands. However, the underlying mechanisms of the positive relationships between tree species diversity and ecosystem functioning have so far been analyzed mainly for aboveground processes, with less attention paid to the role of belowground functions.
To fill this knowledge gap, researchers from the Chair of Silviculture, as part of a pan-European project (SoilForEUROPE), investigated the influence of tree diversity on fine-root soil exploitation in four European forest types in Finland, Poland, Romania, and Italy.
In a first study they found that across the four sites, absorbing fine-root biomass was lower in mixtures, but root length density in the topsoil was higher than in mono-specific stands, indicating an increased soil resource uptake capacity by trees in mixtures.
Further analysesshowed that the decrease in fine-root biomass in mixtures compared to mono-specific stands was related to changes in other fine-root traits. For example, fine roots in mixtures were characterized by higher specific root lengths, smaller diameters, lower tissue densities, and higher nitrogen concentrations. Overall, this indicated that trees in mixtures followed different strategies for resource uptake compared to trees in mono-specific stands. The higher ectomycorrhizal colonization intensity of absorbing fine roots and the higher diversity and abundance of ectomycorrhizae in soil samples indicated positive biotic feedbacks from mycorrhizae, which could significantly enhance soil resource exploitation by trees in mixtures.
Overall, these results significantly enhance our understanding of the functioning of mixed-species forests. They provide evidence that below-ground interactions between different tree species in mixtures can enhance the uptake of soil resources by trees.
Original publications:
Wambsganss, J., Beyer, F., Freschet, G.T., Scherer-Lorenzen, M., Bauhus, J. (2021): Tree species mixing reduces biomass but increases length of absorptive fine roots in European forests. Journal of Ecology, 109, 2678-2691.
Wambsganss, J., Freschet, G.T., Beyer, F., Scherer-Lorenzen, M., Bauhus, J. (2021): Tree species mixing causes a shift in fine-root soil exploitation strategies across European forest types. Functional Ecology, 35, 1886-1902.
