Influence of different land use intensities and plant richness pattern on microbial ammonium turnover in grassland ecosystems

 

 

Scientific investigators:

Prof. Dr. Michael Schloter

Prof. Dr. Jean Charles Munch

Annabel Meyer

(Helmholtz Center München)

Hypotheses:

  1. Land use and biodiversity pattern shape transformation processes in soil.

  2. In contrast to developing ecosystems all sites under investigation in the exploratories have reached the climax state, resulting in a maximum of microbial diversity in soil.

  3. Although the rhizosphere of different annual plants harbours similar microbial communities with similar genetic gene expression rates differs highly. Consequently transformation processes are not limited by missing genetic potential but are regulated by biotic factors like plant exsudates as well as plant litter, the climate and land use, which regulate expression of specific microbial genes.

Soil microbial communities are the key factor for a sustainable land use. Bacteria, fungi and Archaea act as drivers for all major nutrient cycles and control therefore plant development and soil quality. To acknowledge this important role of soil microbes the term “genetic soil treasures” was established in the last years. In most cases the activity of microbes cannot be related to one particular strain or ecotype as interacting communities are the drivers for selected functions. Moreover many processes are closely interlinked and one turnover process directly influences other metabolic pathways. Two major factors have been identified, that are responsible for sustainable turnover rates: Implying that different microorganisms in an ecosystem use different ecological niches, and differentially contribute to the distinct processes under variable conditions, their diversity and abundance can be taken as a measure for the stability of an ecosystem. Which factor counts more is still under debate and might be more dependent on the pathway that we are looking at and on the ecosystem.
According to the UN Milleniums report the nitrogen input to the environment has doubled in the last 50 years accompanied by a significant reduction of biodiversity. However nitrogen is one of the elemental nutrients for all organisms. Five major microbial processes contribute to the geobiochemical cycling of nitrogen in aerobic terrestrial soils: nitrogen fixation (N2 ? NH4+), mineralization (orgN ? NH4+), nitrate ammonification (NO3? ? NH4+), nitrification (NH4+ ? NO3?) and denitrification (NO3? ? N2). The rates at which these metabolic pathways occur determine the availability of N in the soil and therefore the activity of soil microorganisms and plant growth in agricultural ecosystems. Besides bacteria, also fungi and Archaea are mainly involved in nitrogen turnover. The aim of this project is to identify microorganisms involved in N-cycling, to determine the microbial potential (gene pool), its induction (transcript pool) and the activity (enzyme pool) for the various nitrogen transformations at hot spots of well characterized grassland sites in the three exploratories, which are under different management. These hot spots include the rhizosphere and the litter layer. We want to address questions related to influence of management on diversity and abundance pattern of microbial communities involved in nitrogen turnover under the influence of different farming management, based on the genome, transcriptome and proteome level.

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