The importance of C, N and P as driver for bacterial community structure in German beech dominated forest soils.

Among several environmental factors shaping soil microbial communities the impact of soil nutrients is of special interest. While continuous application mainly of N and P dramatically shifts community composition during fertilization, it remains unclear whether this effect is consistent in generic, unfertilized beech forest ecosystems of Germany, where differences in nutrient contents are mostly a result of the parental material and climatic conditions. We postulate that in such ecosystems nutrient effects are less pronounced due to the possibility of the soil microbiome to adapt to the corresponding conditions over decades and the vegetation acts as the major driver. To test this hypothesis, we investigated the bacterial community composition in five different German beech dominated forest soils, representing a natural gradient of total- and easily available mineral-P. A community fingerprinting approach was performed using terminal-Restriction Fragment Length Polymorphism analysis of the 16S rRNA gene, while abundance of bacteria was measured applying quantitative real-time PCR. Bacterial communities at the five forest sites were distinctly separated, with strongest differences between the end-members of the P-gradient. However the majority of identified microbial groups (43%) were present at all sites, forming a core microbiome independent from the differences in soil chemical properties. Especially in the P-deficient soil the abundance of unique bacterial groups was highly increased, indicating a special adaption of the community to P limitation at this site. In this regard Correspondence Analysis elucidated that exclusively soil pH significantly affected community composition at the investigated sites. In contrast soil C, N and P contents did mainly affect the overall abundance of bacteria