Tree species mixing affects soil microbial functioning indirectly via root and litter traits and soil parameters in European forests

By Lauren M. Gillespie, S. Hättenschwiler, A. Milcu, Janna Wambsganss, Ammar Shihan, N. Fromin. Functional Ecology, 2021

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2. Here, we sought to evaluate how forest floor litter and absorptive roots affect broad 23 functions of soil microbial communities, and how this may be influenced by tree species 24 mixing. To do so, forest floor litter, absorptive roots, and soil were sampled from mono- 25 specific and 3-species mixed stands in four mature, natural forest ecosystems across 26 Europe. The direct effects of tree species mixing, its indirect effects via litter and root 27 traits, and the effects of soil parameters on microbial biomass, catabolic activity and 28 diversity, and denitrification were analyzed. 29 3. Results did not show direct tree mixture effects on the soil microbial parameters we 30 measured but did suggest indirect influences via tree mixture effects on traits of 31 aboveground litter and absorptive roots and soil parameters. Mixed forests composed of 32 any three tree species modified soil microbial functioning by influencing nutrient 33 availability in forest floor litter and root resource acquisition. Tree mixing also modified 34 soil microbial functioning and catabolic diversity by influencing soil fertility and 35 physicochemical properties. 36 4. Our findings suggest an indirect but present influence of tree species mixing on the 37 activity of heterotrophic soil microbial communities across four different forest 38 ecosystems ranging from Mediterranean to boreal forests. Our study contributes to a 39 better mechanistic understanding of mixed tree species effects on soil microbial 40 functioning via the modification of forest floor litter properties and traits of absorptive 41 roots represented by the tree community beyond simple species numbers consideration, 42 and potentially via soil properties. 43

Subfields: Environmental Chemistry, Nature and Landscape Conservation, Soil Science

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