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Biomedical subjects

P Marschner

Publications and source records attributed to P Marschner.

7 recordsLinked to original sources
PubMed2006

The veterinary antibiotic oxytetracycline and Cu influence functional diversity of the soil microbial community.

There are increasing concerns over the effects of veterinary antibiotics and heavy metals in agricultural soils. The widely used veterinary antibiotic oxytetracycline (OTC), Cu and their combination on soil microbial community function were assessed with the Biolog method. The microbial community was extracted from the soil and exposed to a 0.85% sodium chloride solution containing OTC (0, 1, 5, 11, 43, 109 and 217 microM), or Cu (0, 10, 20, 100 and 300 microM), or combination of the two pollutants (OTC 0, 5, 11 microM and Cu 0, 20 microM). Functional diversity, evenness, average well color development (AWCD) and substrate utilization decreased significantly with increasing concentrations of OTC or Cu (p < 0.005). The critical concentrations were 11 microM for OTC and 20 microM for Cu. The combination of OTC and Cu significantly decreased Shannon's diversity, evenness and utilization of carbohydrates and carboxylic acids compared to individual one of the contaminants. The antibiotic OTC and Cu had significant negative effects on soil microbial community function, particularly when both pollutants were present.

Anti-Bacterial Agents↗
PubMed2005

Methane production and microbial community structure in single-stage batch and sequential batch systems anaerobically co-digesting food waste and biosolids.

Anaerobic co-digestion of food waste and biosolids was carried out in sequential batch and single-stage batch systems in four treatments. Methane yield, which was used as a functional process parameter, differed between treatments, with the single-stage batch system generating lower volumes than the sequential batch systems. Volatile fatty acid (VFA) concentrations and pH in the leachate also differed between treatments. VFA concentrations were highest and methane generation yields lowest in the single-stage batch system in comparison to the sequential batch systems. The anaerobic microbial community structure of the domains Archaea and Bacteria, determined by denaturing gradient gel electrophoresis, differed between treatments and was correlated to a number of environmental parameters such as pH, VFA concentration and methane generation rate. Methane generation rate was significantly correlated to the community structure of Bacteria but not Archaea. This indicated that the substrates that are produced by acetogens (Bacteria) are important for the growth and community structure of the methanogens (Archaea). Community structure of Archaea changed over time, but this had no observable effect on functional ability based on methane yields. Microbial diversity (H') was shown to be not important in developing a functionally successful anaerobic microbial community.

Anaerobiosis↗
PubMed2005

Nutrient availability and management in the rhizosphere: exploiting genotypic differences.

Crop nutrition is frequently inadequate as a result of the expansion of cropping into marginal lands, elevated crop yields placing increasing demands on soil nutrient reserves, and environmental and economic concerns about applying fertilizers. Plants exposed to nutrient deficiency activate a range of mechanisms that result in increased nutrient availability in the rhizosphere compared with the bulk soil. Plants may change their root morphology, increase the affinity of nutrient transporters in the plasma membrane and exude organic compounds (carboxylates, phenolics, carbohydrates, enzymes, etc.) and protons. Chemical changes in the rhizosphere result in altered abundance and composition of microbial communities. Nutrient-efficient genotypes are adapted to environments with low nutrient availability. Nutrient efficiency can be enhanced by targeted breeding through pyramiding efficiency mechanisms in a desirable genotype as well as by gene transfer and manipulation. Rhizosphere microorganisms influence nutrient availability; adding beneficial microorganisms may result in enhanced availability of nutrients to crops. Understanding the role of plant-microbe-soil interactions in governing nutrient availability in the rhizosphere will enhance the economic and environmental sustainability of crop production.

Breeding↗
PubMed1997

Iron Stress and Pyoverdin Production by a Fluorescent Pseudomonad in the Rhizosphere of White Lupine (Lupinus albus L.) and Barley (Hordeum vulgare L.).

Induction of high-affinity iron transport during root colonization by Pseudomonas fluorescens Pf-5 (pvd-inaZ) was examined in lupine and barley growing in microcosms. P. fluorescens Pf-5 (pvd-inaZ) contains a plasmid carrying pvd-inaZ; thus, in this strain, ice nucleation activity is regulated by pyoverdin production. Lupine or barley plants were grown for 18 or 8 days, respectively, in soil amended with 2% calcium carbonate and inoculated with P. fluorescens Pf-5 (pvd-inaZ) at a density of 4 x 10(sup8) CFU g (dry weight) of soil(sup-1). A filter paper blotting technique was used to sample cells from the rhizosphere in different root zones, and then the cells were resuspended for enumeration and measurement of ice nucleation activity. The population density of P. fluorescens Pf-5 (pvd-inaZ) in the rhizosphere decreased by one order of magnitude in both lupine and barley over time. The ice nucleation activity ranged from -3.4 to -3.0 log ice nuclei CFU(sup-1) for lupine and -3.0 to -2.8 log ice nuclei CFU(sup-1) for barley, was similar in all root zones, and did not change over time. An in vitro experiment was conducted to determine the relationship between ice nucleation activity and pyoverdin production in P. fluorescens Pf-5 (pvd-inaZ). An ice nucleation activity of approximately -3.0 log ice nuclei CFU(sup-1) was measured in the in vitro experiment at 25 to 50 (mu)M FeCl(inf3). By using the regression between ice nucleation activity and pyoverdin production determined in vitro and assuming a P. fluorescens Pf-5 (pvd-inaZ) population density of 10(sup8) CFU g of root(sup-1), the maximum possible pyoverdin accumulation by P. fluorescens Pf-5 (pvd-inaZ) in the rhizosphere was estimated to be 0.5 and 0.8 nmol g of root(sup-1) for lupine and barley, respectively. The low ice nucleation activity measured in the rhizosphere suggests that nutritional competition for iron in the rhizosphere may not be a major factor influencing root colonization by P. fluorescens Pf-5 (pvd-inaZ).

Journal Article↗
PubMed1993

The effect of Paxillus involutus Fr. on aluminum sensitivity of Norway spruce seedlings.

Non-mycorrhizal Norway spruce seedlings (Picea abies Karst.) and Norway spruce seedlings colonized with Paxillus involutus Fr. were grown in an axenic silica sand culture system. After successful mycorrhizal colonization, the seedlings were exposed to 200 or 800 micro M AlCl(3) for 10 weeks. In both non-mycorrhizal and mycorrhizal seedlings, exposure to Al significantly reduced root growth and the uptake of Mg and Ca. After 5 weeks of exposure to 800 micro M Al, the mycorrhizal seedlings had significantly higher chlorophyll concentrations than the non-mycorrhizal seedlings, although no difference in Mg nutrition was apparent. After 10 weeks of exposure to Al, both non-mycorrhizal and mycorrhizal seedlings exhibited needle chlorosis and reduced photosynthetic activity. However, the aluminum-induced reduction in shoot growth was largely ameliorated by colonization with P. involutus. We conclude that mycorrhizal colonization modifies the phytotoxic effects of Al in Norway spruce seedlings. However, differences in physiological responses to Al between mycorrhizal and non-mycorrhizal seedlings may be largely reduced in the long term as a result of impaired mineral nutrient uptake.

Journal Article↗