ifoam'96 Book of Abstracts 11th IFOAM Scientific Conference 11-15 August 1996, Copenhagen, Denmark

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Workshop

Metabolic diversity of microbes in biological and conventional soils.W27/P3

1) Research Institute of Organic Agriculture (FiBL), CH-4104 Oberwil, 2) Department of Botany, CH-4056 Basel

Soil microorganisms are living in complex communities, where they are responsible for nutrient recycling and the degradation of problematic xenobiotics. The current decrease in biodiversity has aroused interest in quantifying the impact on the biotic component of soil ecosystems in view of the sustainability of agricultural systems.
Ecological studies are considering community structure (species diversity) and/or function (rate of specific processes). There are several experimental approaches to assess the diversity of microbial populations, most of them are relying on isolation and culture techniques based on physiological tests, and, more recently, on fatty acid profiles, protein analysis, nucleic acid hybridization, or DNA fingerprinting. Isolation of microbial populations, however, selects only for a minority of organisms. One recently developed method, that avoids the isolation process, assesses the immediate carbon source utilization of whole environmental samples, using BIOLOG microplates with 95 different carbon sources (Garland and Mills,1991) (BIOLOG Inc., Hayward, Cal.). Metabolic fingerprints as assessed by this method can be considered to reflect characteristic soil properties with respect to actual or potential microbial activities.
It was the aim of our investigations to determine whether this carbon source utilization assay can be used to detect changes in microbial communities that might have occurred in soils under different agricultural management. As microbial biomass and overall microbial activities have been found to differ significantly in soils of different farming systems (Mäder et al., 1993), it was expected that differences may occur also at the community level of soil populations.
Substrate use patterns of soil microbial communities appear to reflect actual or potential metabolic activities of soils. There is evidence that this method allows to differentiate between soils of different agricultural systems. Clearly, there are seasonal effects to be considered, as well as the influence of vegetation and short-term effects of amendments.

Garland, J. L. and Mills, A. L. (1991): Classification and Characterization of Heterotrophic Microbial Communities on the Basis of Patterns of Community Level Sole Carbon Source Utilization. Appl. Environ. Microbiol. 57: 2351-2359.

Mäder, P., Huesch, S., Niggli, U. and Wiemken, A. (1995) Metabolic activities of soils from biodynamic, organic and conventional production systems. In: Cook, H.F. and Lee, H.C. (eds.) Soil Management in Sustainable Agriculture 584-587.