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  • 1
    Language: English
    In: Pedobiologia - Journal of Soil Ecology, May 2016, Vol.59(3), pp.93-104
    Description: Soil microorganisms are frequently attached to mineral surfaces or organo-mineral complexes, yet little is known about the microbial colonization of different soil minerals. The use of artificial soils that differ only in their mineral composition (illite, montmorillonite, ferrihydrite, boehmite) and the presence of charcoal, but not in soil texture and organic composition, offered a unique opportunity to study composition, function and succession of soil microorganisms colonizing newly exposed organo-mineral surfaces. Artificial soils were incubated with a microbial inoculum from an arable topsoil at constant temperature (20 °C) and moisture conditions for up to 18 months. The succession of enzyme activities involved in C-, N- and P-cycling gave clear evidence that nutrient limitation drove microbial community structure during the incubation independent of mineral composition. Discriminant analyses of principal components of PLFAs showed that microbial community structure changed over a period of 18 months toward similar communities for all artificial soils at the end of incubation. This was supported by a shift in the soil microbial community from dominance of specific phyla like , which is often referred to as copiotrophic organisms, during the first 6 months of the incubation, toward systems with a higher dominance of e.g. , which are suggested to follow the oligotrophic life-strategy. The effect of mineral surface properties on enzyme activities was pronounced during the first 6 months of incubation. Microbial colonization and succession on mineral surfaces was likely affected by mineral properties such as surface charge and, at the end of incubation, availability of beneficial nutrients. Charcoal affected the microbial community only during the first 6 months of incubation with slightly increased colonization by bacteria which are often described as oligotrophic organisms. In contrast, illite and montmorillonite probably provided nutrient rich environments with montmorillonite supplying more exchangeable cations. The artificial soils experiment clearly showed that changes in substrate availability as well as mineral properties are important drivers for the development of microbial communities.
    Keywords: Clay Minerals ; Fe Oxides ; Charcoal ; Taxa ; Substrate Availability ; Agriculture ; Biology ; Zoology
    ISSN: 0031-4056
    E-ISSN: 1873-1511
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  • 2
    Language: English
    In: Pedobiologia - Journal of Soil Ecology, July 2019, Vol.75, pp.1-7
    Description: It is known that earthworms can increase the content of water-extractable silicon (Si) in soil, thus contributing to the availability of Si for plants. However, effects of earthworms on other Si fractions in soil, such as adsorbed Si, Si bound to SOM, Si occluded in pedogenic oxides and amorphous silica have not yet been studied. Therefore, we investigated the effects of the endogeic earthworm Savigny on the fractionation of Si in soils and that of the epigeic earthworm Bouché on the release of Si from model substances (quartz, wheat straw, bioopal). We quantified the amounts of Si in different soil fractions and those released from model substances before and after passage through the earthworm gut by sequential Si extraction. The amounts of Si extracted from the earthworms’ casts were generally larger than in the undigested samples. This was especially pronounced for Si bound to soil organic matter (SOM; up to 41%), and for Si in wheat straw (up to 71%) and quartz (up to 1730%). With the soils, the increase in extracted Si was pronounced for the more mobile fractions (Si bound to SOM and occluded in pedogenic oxides) at the expense of amorphous silica. The amounts of mobile and adsorbed Si (plant-available Si) in soil tended to decrease after the passage through the earthworm gut, possibly by occlusion of adsorbents in aggregates formed in the gut. Our results indicate that both mechanical weathering of ingested Si-containing particles and microbial processes, promoting aggregate formation, SOM transformation and mineral solubilization, contribute to the increased release of Si, which induced the redistribution of Si among fractions.
    Keywords: Sequential Extraction ; Silicic Acid ; Octolasion Cyaneum Savigny ; Eisenia Andrei Bouché ; Aggregates ; Agriculture ; Biology ; Zoology
    ISSN: 0031-4056
    E-ISSN: 1873-1511
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