Microbial community composition in the rhizosphere of Larix decidua under different light regimes with additional focus on methane cycling microorganisms.

Microbial community and diversity in the rhizosphere is strongly influenced by biotic and/or abiotic factors, like root exudates, nutrient availability, edaphon and climate. Here we report on the microbial diversity within the rhizosphere of Larix decidua, a dominant tree species in the Alps, as compared with the microbiome within the surrounding soil. We describe how increased light intensity influenced the rhizobiome and put emphasize on methane cycling microorganisms. Microbial taxa were classified into 26 bacterial, 4 archaeal and 6 fungal phyla revealing significant differences between bulk and rhizosphere soils. The dominant prokaryotic phyla were Proteobacteria, Acidobacteria, Actinobacteria (both, rhizosphere and bulk soil) and Bacteroidetes (rhizosphere soil only) and dominant fungal phyla in both fractions included Ascomycota and Basidiomycota. The rhizosphere community was indicated by Suillus sp., plant growth-promoting bacteria and Candidatus Saccharibacteria. Predicted genes in membrane transport and carbohydrate metabolism were significantly more abundant in rhizosphere soils while genes connected with energy metabolisms and cell motility increased in bulk soils. Dominant methanotrophic microorganisms were Upland Soil Cluster (USC) α methanotrophs, Methylogaea spp. and Methylosinus spp., while most methanogens belonged to Methanomassiliicoccales. The overall abundance of methanotrophs distinctly increased in the rhizosphere but to a very different species-specific extent. The increased light intensity only led to minor changes in the rhizobiome, nevertheless a couple of indicator species (e.g. Pseudomonas sp.) for intensified light conditions were established.