Given the climate scenarios, we expect in future an increasing frequency of extreme meteorological boundary conditions that result in a higher frequency of drying/rewetting and freezing/thawing of soils. The latter might be especially relevant in higher elevation sites. Such drastic changes of the meteorological boundary conditions to soils, which occur irregularly and with varying intensity are obviously influencing the turnover of C, N and S in soils to a larger extend than previously thought. Our knowledge about the mechanisms and relevance of such conditions for soil processes is very limited. One reason for that is the lack of field experiments.
The goal of the Research Unit is thus to investigate:
-- Which are the consequences of extreme meteorological boundary conditions for the element turnover and -output from soils as well as for microbial communities and roots?
-- What is the effect of different intensities of drying and frost?
-- What are the physical, biological and chemical mechanisms that cause the effects?
These questions can only be addressed by an interdisciplinary Research Unit comprising soil scientists, hydrologists, microbiologists and plant ecologists. In a Norway Spruce forest (Podsol) and a fen (Histosol) we will experimentally initiate drying by roof construction and drainage, respectively, followed by controlled rewetting. Frost intensity of the forest soil will be enlarged by removal of the snow cover. In addition, laboratory experiments with soil columns will be conducted. The focus is on the emission of trace gases, the transport in solution and the related processes (C- and N-mineralisation, nitrification, denitrification, DOC-release, methanogenesis, redoxreactions of S and Fe, formation of flow paths). Mechanisms will be investigated by identifying reactive soil fractions, by following root turnover and microbial community changes. Advanced methods, like component specific C13, N15, O18 analysis, determination of C14 age, biomarker and molecular analyses will be used. We expect that this research will substantially enhance our understanding of soil processes in general.
Through the joined field and laboratory experiments, coordinated sampling and data evaluation of results, the Research Unit will gain a maximum of synergism, integration and innovation.

DFG Programme Research Units

• Growth and vitality of fine roots of Norway spruce as influenced by experimental and natural drought (Applicant Leuschner, Christoph )
• Microbial cycling of iron in acidic fens (Applicant Küsel, Kirsten )
• Operation of the central experimental sites (Applicant Matzner, Egbert )
• Processes of litter and soil organic matter transformation during extreme drying/wetting as assessed by compound-specific isotope approaches (Applicant Glaser, Bruno )
• Quantification and process analysis of biogenic trace gas fluxes (Applicant Gebauer, Gerhard )
• Response of belowground carbon, sulphur and iron cycling in fen soils (Applicant Blodau, Christian )
• Response of flow systems in soils to extreme atmosperical boundary conditions (Applicant Huwe, Bernd )
• Response of N turnover, DOC production and soil solution fluxes (Applicant Borken, Werner )
• Structural and Functional Links between Denitrifiers, Fermenters and Methanogens: Impact on Greenhouse Gases (Applicant Horn, Marcus A. )
• Structurally optimized modeling of non-linear effects of meteorological extreme events on water and solute dynamics (Applicant Fleckenstein, Jan )

Spokesperson Professor Dr. Egbert Matzner