Traceability of compost amendment by VOC emission patterns

Compost treatment is known to exert several positive effects on soil physical, chemical and biological properties. The change of soil microbial communities may affect plant growth, either through the stimulation of plant growth promoting bacteria, the induction of plant disease suppressiveness, or by the introduction of plant pathogens. In any case, the traceability of signature microorganisms from organic amendments like composts is important when dealing with food safety and food quality. The basis of the present study will be a unique long-term trial comparing four different composts (produced of source-separated domestic organic waste, green cut, manure and sewage sludge) and mineral fertilization that was established in 1991. In a previous study we were able to demonstrate that at various levels of resolution both with structural (PCR-DGGE with specific primers) and functional approaches (community level physiological profiling CLPP) the different composts left distinct imprints. However, a clear disadvantage of all these methods is the need of an extraction step and with CLPP, a cultivation step that biases the results. Microorganisms produce many different volatile organic compounds (VOC). They are produced as coproducts of different metabolic pathways of the secondary metabolism and may be either waste products or used as signal substances. Some VOCs are characteristically produced by specific phylogenetic groups or species. In a preliminary experiment using PTR-MS (Proton Transfer Reaction Mass Spectrometer) we found that the different composts emitted a distinct pattern of volatile organic compounds (VOCs). This encouraged us to use this approach to trace compost use in soils, thus avoiding extraction and cultivation steps, and advancing from soil genomics to soil metabolomics. The first hypothesis is that VOC emission patterns are able to discriminate between soils that have been treated with composts and those that have not. The second, more specific hypothesis is that it will even be possible to discriminate among different types of composts. Thirdly, we hypothezise that the VOC emission patterns are discriminating the soils in the same way as the genotype-based approaches and thus indicate metabolic processes carried out by the microbial community at the time of sampling. Soil samples will be taken from 6 selected treatments (contol, 80 kg mineral N ha -1 , 4 different composts+mineral N). For the genotypic characterisation of the microbial community denaturing gradient gel electrophoresis (DGGE) and CompoChip microarrays (developed in our laboratory) using PCR amplified community 16S and 18S rDNA for bacteria and fungi, respectively, will be employed. VOC measurement will be performed by PTR-MS technology. Co-inertia analyses will be conducted in order to determine correlations between microbial community patterns and VOC emission patterns.

Compost treatment is known to exert several positive effects on soil physical, chemical and biological properties. The change of soil microbial communities may affect plant growth, either through the stimulation of plant growth promoting bacteria, the induction of plant disease suppressiveness, or by the introduction of plant pathogens. In any case, the traceability of signature microorganisms from organic amendments like composts is important when dealing with food safety and food quality. The basis of the present study will be a unique long-term trial comparing four different composts (produced of source-separated domestic organic waste, green cut, manure and sewage sludge) and mineral fertilization that was established in 1991. In a previous study we were able to demonstrate that at various levels of resolution both with structural (PCR-DGGE with specific primers) and functional approaches (community level physiological profiling - CLPP) the different composts left distinct imprints. However, a clear disadvantage of all these methods is the need of an extraction step and with CLPP, a cultivation step that biases the results. Microorganisms produce many different volatile organic compounds (VOC). They are produced as coproducts of different metabolic pathways of the secondary metabolism and may be either waste products or used as signal substances. Some VOCs are characteristically produced by specific phylogenetic groups or species. In a preliminary experiment using PTR-MS (Proton Transfer Reaction Mass Spectrometer) we found that the different composts emitted a distinct pattern of volatile organic compounds (VOCs). This encouraged us to use this approach to trace compost use in soils, thus avoiding extraction and cultivation steps, and advancing from soil genomics to soil metabolomics. The first hypothesis is that VOC emission patterns are able to discriminate between soils that have been treated with composts and those that have not. The second, more specific hypothesis is that it will even be possible to discriminate among different types of composts. Thirdly, we hypothezise that the VOC emission patterns are discriminating the soils in the same way as the genotype-based approaches and thus indicate metabolic processes carried out by the microbial community at the time of sampling. Soil samples will be taken from 6 selected treatments (contol, 80 kg mineral N ha -1 , 4 different composts+mineral N). For the genotypic characterisation of the microbial community denaturing gradient gel electrophoresis (DGGE) and CompoChip microarrays (developed in our laboratory) using PCR amplified community 16S and 18S rDNA for bacteria and fungi, respectively, will be employed. VOC measurement will be performed by PTR-MS technology. Co-inertia analyses will be conducted in order to determine correlations between microbial community patterns and VOC emission patterns.