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Prof. Dr. Michael Friedrich

Tim Richter-Heitmann

(Uni Bremen)

Prof. Dr. Jörg Overmann

Dr. Johannes Sikorski

Selma Vieira

(DSMZ Braunschweig)

Hypotheses:

1. Particular species of Acidobacteria and Actinobacteria catalyse the degradation of refractory organic carbon and plant litter, and dominate in bulk soil particles.

2. Specifically adapted Alphaproteobacteria constitute a dominant fraction within the plant rhizosphere and control the flux of organic carbon from plants to the soil environment.

3. Different species of Acidobacteria, Actinobacteria, and Alphaproteobacteria are adapted to and occur under different environmental conditions in bulk soils.

ProFunD focuses on bacterial species involved in the degradation of root exudates and leaf litter that dominate different soil compartments, with the aim to better understand the links between functional bacterial biodiversity, plant diversity and productivity, edaphic factors and land use.

Bacteria can constitute up to 60-80% of all soil microbiota and are important determinants of the biogeochemical cycling of nutrients, of soil fertility and pathogen control. The specific composition of soil bacterial communities is likely to control major ecosystem processes. Evidence has shown that members of the Acidobacteria, Actinobacteria and Alphaproteobacteria are distributed in the soil environment in a non-random fashion and preferentially colonize different compartments. Differences in the overall composition of the bacterial community across different soil compartments are expected to have major effects on organic carbon sequestration, nutrient regeneration and turnover, and on the microbial food chain. Yet, very little is known on the partitioning of  different  species  of  these bacterial groups  in  the  soil environment,  their  abiotic  and  biotic  controls,  and  the  functional  implications  of  these  diversity patterns for the carbon and nutrient cycling.

This work intends to determine the partitioning of active Acidobacteria, Actinobacteria, and Alphaproteobacteria between the rhizosphere of dominant plant species and the bulk soil particles and to quantify the functions of dominant members of these three groups in the soil carbon fluxes under different ecological conditions.

• The distribution of individual species  of  Acidobacteria,  Actinobacteria,  and  Alphaproteobacteria  between  the  rhizosphere  of six dominant  plant  species  and  bulk  soil  particles  will  be  systematically  studied  by  high  throughput Illumina sequencing of the 16S rRNA and will then be related to the specific composition of plant exudates, specific plant traits, physicochemical soil parameters and land use.
• The contribution of bacteria affecting the C- and N-transfer from plant roots to bulk soil, and from plant litter to bulk soil, will be evaluated in a series of Functional  Diversity  Mesocosm   experiments. We will apply a combination of ¹³C/ ¹⁵N-RNA Stable Isotope Probing (SIP) and ¹³C-RNA Captured RNA Isotope Probing (CARIP) to probe the assimilatory capabilities of these bacteria and deduce their different functions in soil.
• The relative abundance of Acidobacteria, Actinobacteria and Alphaproteobacteria in all 300 experimental plots (EPs) will be quantified by qPCR of the 16S rRNA, as a prerequisite for a better understanding of the interrelation between these bacteria, plant diversity, edaphic factors and land use.

Work will be conducted  in  close  cooperation  with  several  other  microbiological  projects,  as  well  as  with  plant and soil-based studies to enable data integration and synthesis.