%0 Generic
%F orgprints:6047
%K microbial diversity, DOK trial, C4-crop, C3-vegetation, 13C/12C-isotopic, DOK, Bodenfruchtbarkeit
%T Kohlenstoffflüsse und mikrobielle Diversität
%U https://orgprints.org/id/eprint/6047/
%X Organic farming is one of the most promising alternatives to intensive agriculture. Crop plant-soil interactions are complex and influenced by agricultural practice. Many efforts have been done to elucidate the effects of different farming systems on crop growth, nutrient availability, soil quality and biodiversity. Many studies however are short-termed and rely on laboratory rather than comparative field experiments. The DOK field trial at Therwil (Basel-Land, Switzerland) is one of the few long-term field trials that compare organic and integrated farming systems since 1978 (Mäder et al. 2002, http://www.fibl.org/). Soils of this field trial have been extensively studied with respect to soil nutrient delivery, soil biology and microbial biodiversity. Organically managed soils efficiently produced crops at lower level of input and exerted positive effects on soil quality and biodiversity. Soil microorganisms are important in the cycling of carbon and plant nutrients, and are taken as bioindicators of soil quality. Results of the DOK trial indicate a more efficient resource utilisation in organic treated soils, possibly due to increased soil microbial activity. We postulate that a highly diverse and active microbial community may accelerate decomposition of plant organic matter and increase turnover of carbon uptake in organic managed soils of the DOK trial.  In the proposed study we intend to measure carbon fluxes from the crop plant to the soil microbial pool under field conditions. We would like to determine, which members of the microbial community are most actively involved in decomposition and plant derived carbon uptake in different farming systems. The discrimination of plant derived carbon from native soil organic carbon is now possible, since maize, a C4-crop, is grown for the first time in the long-term DOK field trial that previously has been dominated by a C3-vegetation. We will use stable isotope techniques to identify C4-crop induced changes in soil carbon pools and fluxes by calculating the difference in the 13C/12C-isotopic ratio of the crop plant and the soil. Microorganisms that are actively involved in decomposition and uptake of plant derived carbon will be traced by 13C. We will also use phospholipid fatty acid (PLFA) profiling to specify microbial groups and changes in the microbial community. PLFA are specific components of cell membranes only found in intact cells and are indicative of major microbial groups. Additionally, the 12C/13C signature of individual PLFAs will determine microorganisms involved in active uptake of maize derived 13C.  Since 13C phospholipid fatty acids have hardly been investigated by the use of a natural abundance 13C approach, the application of this technique can be regarded as pioneer work in the field of microbial ecology. Assumably, active microbial populations can be distinguished from those that are not utilizing the plant-derived carbon sources. The outcome of this project will provide new insights in functional properties of the microbial community in soils of sustainable farming systems  We would like to determine, which members of the microbial community are most actively involved in decomposition and plant derived carbon uptake in different farming systems. We will use phospholipid fatty acid (PLFA) profiling in combination with stable carbon isotope techniques. PLFA profiling will allow the characterization of microbial phylogenetic groups whereas 12C/13C signature of individual PLFAs will assign specific microorganisms involved in active uptake of plant derived carbon. The difference in the 13C/12C-isotopic ratio of the crop plant and the soil, allows for identifying C4-crop induced changes in soil carbon pools and fluxes. Carbon derived from the maize can be distinguished from Carbon derived from soil organic matter mineralization. Root exudates are partly incorporated into soil microorganisms and partly mineralized to CO2. The flux rate and pool size changes will allow for an estimate of root biomass and turnover and indicate carbon utilisation efficiency of soil microbes.   The contribution of root exudates and plant residues to soil organic matter fractions that are actively involved in soil processes will be measured, and thus, it is expected to substantiate previous findings under controlled lab conditions of higher decomposition rates and an enhanced incorporation of available organic carbon to microbial biomass. The acquired data will be integrated to soil carbon modelling approaches with respect to low input and organic farming systems.