Miriam Athmann

Spatial variability of hydrolytic and oxidative potential enzyme activities in different subsoil compartments

The spatial heterogeneity of nutrient turnover in subsoils has been rarely studied in the past, although drilosphere and rhizosphere are found to be important microbial hotspots in this oligotrophic environment. In this study, we measured different potential enzyme activities in different soil compartments of subsoil and topsoil. It could be shown that the activities of hydrolases, which cleave readily available organic substrates, are significantly higher in samples from the drilosphere and rhizosphere both in topsoil and subsoil. In bulk soil, hydrolase activities decrease with depth. In contrast, oxidative enzymes, which are involved in the decay of recalcitrant organic material, are released from the microbial community especially in the bulk fraction of subsoil. This emphasizes the importance of subsoil for nutrient acquisition and gives evidence for a distinct spatial separation of microbes with diverging lifestyles.

Grouping and classification of wheat from organic and conventional production systems by combining three image forming methods

Using image forming methods, products from organic and conventional origin have been discriminated with high accuracy, but the meaning of these differences in terms of product quality is so far poorly understood. The aim of the presented study is therefore to gain further insights into the suitability of image forming methods for food quality evaluation based on wheat samples from a long-term field trial on the comparison of different organic and conventional production systems (DOC-trial). The images of the encoded samples were (1) grouped into pairs with similar image features, (2) characterized based on reference images (e.g. high resistance to degradation – low resistance to degradation), (3) ranked (according to the quality characterization), and (4) assigned to the different production methods (classified). The encoded samples from the production methods mineral fertilization, conventional production (combination of mineral fertilization and farmyard manure) and the class of organic production methods (biodynamic, bioorganic and unfertilized control) could be grouped and classified in both years. Within the class of organic production methods grouping (assigning of similar samples to image categories) and classification (assigning of categories to production methods) was partially possible. The correct grouping and classification of samples from organic and conventional production shows that different fertilization systems influence image structures in a typical and reproducible manner. The evaluation approach followed in the presented research can provide a considerable contribution to advance our understanding of quality differences between products from different farming systems or plant production measures.

Standardization and performance of a visual Gestalt evaluation of biocrystallization patterns reflecting ripening and decomposition processes in food samples

The biocrystallization method is based on the phenomenon that additive-specific, dendritic crystallization patterns emerge when an aqueous dihydrate cupric chloride solution with additives is crystallized on a glass plate. The patterns reflect physiological processes like ripening and decomposition and are applied in differentiating food samples according to feeding regime, production system and degree of processing. The method has been used for decades in organic food quality assessment from an ontological holistic stance. The patterns are evaluated visually and by means of computerized image analysis. The present study describes the development of the visual evaluation from a morphological description of structural features towards the perception of a Gestalt, a salient, coherent ‘meaningful-whole’, which complies more closely with the pattern formation principle of the method. The methodology was standardized according to ISO-Norms 11035 and 8587 for sensory analysis of food products, adapted for use in the visual evaluation of biocrystallization patterns. Two Gestalts, ‘Ripening’ and ‘Decomposition’, reflected in biocrystallization patterns from diverse agricultural products were characterized, trained on and examined. Based on the statistical evaluation, it is concluded that the panel has become reliable and appropriate for ranking biocrystallization patterns according to the intensity of the two Gestalts. The developed level of Gestalt evaluation of biocrystallization patterns provides a basis towards qualitative interpretative judgements on the food quality of a product relating to quality concepts based on plant physiological processes.

Quality characterisation via image forming methods differentiates grape juice produced from integrated, organic or biodynamic vineyards in the first year after conversion

Abstract In this study, the effects on grape juice quality resulting from the conversion of vineyard plots from integrated to organic and biodynamic management vs. integrated management were assessed using image forming methods. In addition, grape yield, Botrytis infection and the chemical composition of wood prunings and grapes were assessed. The images of replicate, encoded samples representing five different treatments were: (i) grouped into pairs displaying similar image features, (ii) characterised with respect to the quality domains ‘strength of form expression’ and ‘resistance to deterioration’ and (iii) ranked according to the quality characterisation. Based on the image analyses, all samples pairs were correctly grouped, i.e. the five production methods were precisely separated. The treatments were characterised as follows: (i) Integrated (INT): weakest form expression, most advanced deterioration; (ii) Conversion to Biodynamic without horn silica (BD0): strongest form expression, advanced deterioration; (iii) Conversion to Organic (ORG): weak form expression, low deterioration; (iv) Conversion to Biodynamic with 3 × horn silica (BD3): medium form expression, low deterioration; (v) Conversion to Biodynamic with 4 × horn silica (BD4): strong form expression, low deterioration. Principal component analysis (PCA) of field assessment and chemical analysis data revealed that the two treatments with the strongest form expression, BD0 and BD4, were characterised by high vigour, as indicated by high prune weight and primary amino nitrogen (NOPA). With respect to the resistance to deterioration, as depicted by image forming methods, no parallels were found with PCA.

Advanced panel training on visual Gestalt evaluation of biocrystallization images: ranking wheat samples from different extract decomposition stages and different production systems

ABSTRACT Biocrystallization images are formed in reaction with foods; in the course of the evaporation of the water from food extracts in presence of copper chloride, crystalline structures are formed. The structures are known to reflect food quality, such as degree of decomposition. Individual expert evaluators have suggested that crystallization images of samples from organic production contain fewer signs of decomposition and that this feature can distinguish organic foods from their conventional counterparts. To further assess the scientific merits of this methodology, a panel of nine evaluators was trained in the visual assessment of biocrystallization images and asked to rank the visual Gestalt decomposition level of encoded images of wheat extracts from i) the same production system at five different decomposition stages and ii) organic production systems vs. conventional production systems aged for the same amount of time. The panel was trained by supervised classification on the basis of defined criteria and intra- and inter-personal variation was assessed. Statistical evaluation showed that the panel was highly reliable, and that the method was appropriate for ranking biocrystallization images of five different decomposition levels. Furthermore, images of samples from organic or conventional production systems could be distinguished with high agreement according to their Gestalt decomposition level with fewer signs of decomposition in the images of organic samples. The rank order between the organic systems vs. the conventional systems was significant.

Bacteria utilizing plant-derived carbon in the rhizosphere of Triticum aestivum change in different depths of an arable soil

Root exudates shape microbial communities at the plant-soil interface. Here we compared bacterial communities that utilize plant-derived carbon in the rhizosphere of wheat in different soil depths, including topsoil, as well as two subsoil layers up to 1 m depth. The experiment was performed in a greenhouse using soil monoliths with intact soil structure taken from an agricultural field. To identify bacteria utilizing plant-derived carbon, 13 C-CO2 labelling of plants was performed for two weeks at the EC50 stage, followed by isopycnic density gradient centrifugation of extracted DNA from the rhizosphere combined with 16S rRNA gene-based amplicon sequencing. Our findings suggest substantially different bacterial key players and interaction mechanisms between plants and bacteria utilizing plant-derived carbon in the rhizosphere of subsoils and topsoil. Among the three soil depths, clear differences were found in 13 C enrichment pattern across abundant operational taxonomic units (OTUs). Whereas, OTUs linked to Proteobacteria were enriched in 13 C mainly in the topsoil, in both subsoil layers OTUs related to Cohnella, Paenibacillus, Flavobacterium showed a clear 13 C signal, indicating an important, so far overseen role of Firmicutes and Bacteriodetes in the subsoil rhizosphere.