Sebastian Bibinger (München / DE), Melissa Wannenmacher (Freiburg i. Br. / DE), Susanne Kublik (München / DE), Christiane Werner (Freiburg i. Br. / DE), Friederike Lang (Freiburg i. Br. / DE), Michael Schloter (München / DE), Stefanie Schulz (München / DE)
In forest ecosystems, the forest floor represents the boundary between mineral soil and atmosphere and as such acts as a hub for microbial nutrient turnover and transport. Likewise, the rhizosphere plays a pivotal role in nutrient turnover and is crucial for both plant nutrition and health. However, how plant-specific rhizosphere selection takes place in the forest floor, a hotspot for fine root biomass, remains insufficiently understood.
The goal of this study was to elucidate, how different tree species (F. sylvatica, A. pseudoplatanus, P. abies) shape their bacterial rhizosphere microbiome in the forest floor as compared to the mineral soil. One the one hand, tree-specific effects are generally thought to dominantly impact the associated microbiome composition, especially based on their differential mycorrhization profiles and nutrient requirements. On the other hand the rhizosphere selection in the forest floor is generally expected to impact the community composition less than in the mineral topsoil, especially with regards to the increase of copiotrophic bacteria.
Rhizosphere samples were collected from the three tree species in two horizons (forest floor and mineral topsoil) at four sites of contrasting climate and at two timepoints (May and September). Bulk soil samples were collected alongside and 16S rRNA gene amplicon sequencing was carried out with all samples.
Microbial community composition but not alpha diversity was impacted by all analysed factors. Surprisingly, the soil compartment had the overall smallest impact on the microbiome composition while the tree species had a strong impact on its associated microbiome irrespective of compartment. The tree-specific selection effect was more pronounced in the mineral soil than in the forest floor as revealed by ordination. 16S rRNA gene copy number prediction hinted at species-specific enrichment of copiotrophic bacteria in the rhizosphere of either the mineral soil or the forest floor.
Findings from this study enhance our understanding of how different tree species influence the composition of their associated microbiome in the mineral soil and in the forest floor.