Background: Photosynthesis is the key process for plant growth and development. The determination... more Background: Photosynthesis is the key process for plant growth and development. The determination of chlorophyll fluorescence kinetics allows the quantification of effects on photosynthetic processes triggered by environmental stress factors such as, e.g., the infection by fungal phytopathogens. The technique is non-invasive, rapid and well suited for experimental field work. Results: Healthy and Uromyces-infected plants of Euphorbia cyparissias were monitored directly in situ in the field using rapid fluorescence kinetics. Non-infected healthy plants show a typical maximum value for the relative variable fluorescence Fv/Fm of around 0.8 with occasional variation between the leaves from the plant top towards the base, while infected plants exhibited a strong gradient to low values at the base. The photosynthetic performance index (PI) showed a higher heterogeneity within the leaves in both plant types. Conclusions: The non-invasive and rapid measurement of chlorophyll fluorescence induction allows characterizing the photosynthetic capacity of healthy and infected plants and of parts of them directly in the field. The PI, is highly sensitive not only concerning infection, but also towards other local environmental influences.
A variety of both lithotrophic and organotrophic microorganisms are known to mediate the mobiliza... more A variety of both lithotrophic and organotrophic microorganisms are known to mediate the mobilization of various elements from solids mostly by the formation of inorganic and organic acids. Under appropriate environmental conditions, metals are solubilized and extracted from metal-rich materials in subsurface ecosystems by the action of bacteria and fungi. In mine tailings or landfills microbial metal leaching represents a
Cell to cell signaling systems in Gram-negative bacteria rely on small diffusible molecules such ... more Cell to cell signaling systems in Gram-negative bacteria rely on small diffusible molecules such as the N-acylhomoserine lactones (AHL). These compounds are involved in the production of antibiotics, exoenzymes, virulence factors and biofilm formation. They belong to the class of furanone derivatives which are frequently found in nature as pheromones, flavor compounds or secondary metabolites. To obtain more information on the relation between molecular structure and quorum sensing, we tested a variety of natural and chemically synthesized furanones for their ability to interfere with the quorum sensing mechanism using a quantitative bioassay with Chromobacterium violaceum CV026 for antagonistic and agonistic action. We were looking at the following questions: 1) Do these compounds affect growth? 2) Do these compounds activate the quorum sensing system of C. violaceum CV026? 3) Do these compounds inhibit violacein formation induced by the addition of the natural inducer N-hexanoylho...
Lake Geneva is a large, holomictic, eutrophic lake with a maximum depth of about 300 m. The sedim... more Lake Geneva is a large, holomictic, eutrophic lake with a maximum depth of about 300 m. The sediments in the central basin have a pillow-like appearance. The soft elevations containing the major portion of the recently sedimented detritus are separated by trenches of 5 to 15 cm depth in which the top sediment layers seem to be missing. Bottom-dwelling fishes
Indoor formation of airborne particles during pre-fermentation grape processing was assessed by p... more Indoor formation of airborne particles during pre-fermentation grape processing was assessed by particle counting using laser particle sizers. Particle numbers of four different aerodynamic size classes (0.3 to 0.5 microm, 0.5 to 1 microm, 1 to 5 microm, and >5 microm) were determined during unloading of harvest containers and subsequent grape stemming and crushing. Regarding these size classes, composition before grape handling was determined as 87.9%, 10.4%, 1.7%, and 0.1%, respectively, whereas the composition changed during grape handling to 50.4%, 15.2%, 33.0%, and 1.5%, respectively. Airborne bacteria and fungi originating from grape processing were collected by impactor and liquid impinger samplers. Grape handling resulted in a sixfold increase in total (biological and non-biological) airborne particles. The generation of bacterial and fungal aerosols was associated mostly with particles of aerodynamic diameters>5 microm (mainly 7 to 11 microm) as determined by flow cytometry. This fraction was increased 150fold in relation to background levels before grape crushing. Maximum concentrations of culturable bacteria reached 485,000 colony forming units (cfu/m3), whereas 146,000 cfu of fungi and yeasts were detected per cubic meter of air. Culturable Gram-negative bacteria occurred only in small numbers (180 cfu/m3). In relation to the total number of airborne particles emitted, culturable microorganisms comprised 0.1% to 0.2%. As soon as grape crushing was stopped, particle concentrations decreased rapidly either due to passive settling or due to air currents in the occupational indoor environment reaching background levels.
Changes in aboveground plant species diversity as well as variations of environmental conditions ... more Changes in aboveground plant species diversity as well as variations of environmental conditions such as exposure of ecosystems to elevated concentrations of atmospheric carbon dioxide may lead to changes in metabolic activity, composition and diversity of belowground microbial communities, both bacterial and fungal. We examined soil samples taken from a biodiversity x CO2 grassland experiment where replicate plots harboring 5, 12, or 31 different plant species had been exposed to ambient or elevated (600 ppm) levels of carbon dioxide for 5 years. Analysis of soil bacterial communities in these plots by temporal temperature gradient gel electrophoresis (TTGE) showed that dominant soil bacterial populations varied only very little between different experimental treatments. These populations seem to be ubiquitous. Likewise, screening of samples on a high-resolution level by terminal restriction fragment length polymorphism (T-RFLP) showed that increased levels of carbon dioxide had no significant influence on both soil bacterial community composition (appearance and frequency of operational taxonomic units, OTUs) and on bacterial richness (total number of different OTUs). In contrast, differences in plant diversity levels had a significant effect on bacterial composition but no influence on bacterial richness. Regarding species level, several bacterial species were found only in specific plots and were related to elevated carbon dioxide or varying plant diversity levels. For example, analysis of T-RFLP showed that the occurrence of Salmonella typhimurium was significantly increased in plots exposed to elevated CO2 (P < 0.05). Plant diversity levels are affecting bacterial composition (bacterial types and their frequency of occurrence). Elevated carbon dioxide does not lead to quantitative alteration (bacterial richness), whereas plant diversity is responsible for qualitative changes (bacterial diversity).
Perspectives in Plant Ecology Evolution and Systematics - PERSPECT PLANT ECOL EVOL SYST, 2005
The influence of plant diversity on belowground ecosystem processes and feedbacks of the latter o... more The influence of plant diversity on belowground ecosystem processes and feedbacks of the latter on plant growth are still largely unexplored. A previous field experiment showed positive effects of plant diversity on diversity and activity of culturable soil bacteria. We examined soil carry-over effects of these experimental communities on subsequent plant growth and the development of soil microbial communities in pots. We inoculated sterile substrate with soil from the field experiment and then sowed three plant species - Dactylis glomerata, Plantago lanceolata and Trifolium pratense - as monocultures or 3-species mixtures into the pots. We measured the phytometers over a period of 14 months. Thereafter, we sampled the soil in 3-species mixtures to analyze microbial communities. The original plant species richness and number of functional groups had positive soil carry-over effects on phytometer germination. Furthermore, in mixtures, species richness also stimulated short-term biom...
Background: Photosynthesis is the key process for plant growth and development. The determination... more Background: Photosynthesis is the key process for plant growth and development. The determination of chlorophyll fluorescence kinetics allows the quantification of effects on photosynthetic processes triggered by environmental stress factors such as, e.g., the infection by fungal phytopathogens. The technique is non-invasive, rapid and well suited for experimental field work. Results: Healthy and Uromyces-infected plants of Euphorbia cyparissias were monitored directly in situ in the field using rapid fluorescence kinetics. Non-infected healthy plants show a typical maximum value for the relative variable fluorescence Fv/Fm of around 0.8 with occasional variation between the leaves from the plant top towards the base, while infected plants exhibited a strong gradient to low values at the base. The photosynthetic performance index (PI) showed a higher heterogeneity within the leaves in both plant types. Conclusions: The non-invasive and rapid measurement of chlorophyll fluorescence induction allows characterizing the photosynthetic capacity of healthy and infected plants and of parts of them directly in the field. The PI, is highly sensitive not only concerning infection, but also towards other local environmental influences.
A variety of both lithotrophic and organotrophic microorganisms are known to mediate the mobiliza... more A variety of both lithotrophic and organotrophic microorganisms are known to mediate the mobilization of various elements from solids mostly by the formation of inorganic and organic acids. Under appropriate environmental conditions, metals are solubilized and extracted from metal-rich materials in subsurface ecosystems by the action of bacteria and fungi. In mine tailings or landfills microbial metal leaching represents a
Cell to cell signaling systems in Gram-negative bacteria rely on small diffusible molecules such ... more Cell to cell signaling systems in Gram-negative bacteria rely on small diffusible molecules such as the N-acylhomoserine lactones (AHL). These compounds are involved in the production of antibiotics, exoenzymes, virulence factors and biofilm formation. They belong to the class of furanone derivatives which are frequently found in nature as pheromones, flavor compounds or secondary metabolites. To obtain more information on the relation between molecular structure and quorum sensing, we tested a variety of natural and chemically synthesized furanones for their ability to interfere with the quorum sensing mechanism using a quantitative bioassay with Chromobacterium violaceum CV026 for antagonistic and agonistic action. We were looking at the following questions: 1) Do these compounds affect growth? 2) Do these compounds activate the quorum sensing system of C. violaceum CV026? 3) Do these compounds inhibit violacein formation induced by the addition of the natural inducer N-hexanoylho...
Lake Geneva is a large, holomictic, eutrophic lake with a maximum depth of about 300 m. The sedim... more Lake Geneva is a large, holomictic, eutrophic lake with a maximum depth of about 300 m. The sediments in the central basin have a pillow-like appearance. The soft elevations containing the major portion of the recently sedimented detritus are separated by trenches of 5 to 15 cm depth in which the top sediment layers seem to be missing. Bottom-dwelling fishes
Indoor formation of airborne particles during pre-fermentation grape processing was assessed by p... more Indoor formation of airborne particles during pre-fermentation grape processing was assessed by particle counting using laser particle sizers. Particle numbers of four different aerodynamic size classes (0.3 to 0.5 microm, 0.5 to 1 microm, 1 to 5 microm, and >5 microm) were determined during unloading of harvest containers and subsequent grape stemming and crushing. Regarding these size classes, composition before grape handling was determined as 87.9%, 10.4%, 1.7%, and 0.1%, respectively, whereas the composition changed during grape handling to 50.4%, 15.2%, 33.0%, and 1.5%, respectively. Airborne bacteria and fungi originating from grape processing were collected by impactor and liquid impinger samplers. Grape handling resulted in a sixfold increase in total (biological and non-biological) airborne particles. The generation of bacterial and fungal aerosols was associated mostly with particles of aerodynamic diameters>5 microm (mainly 7 to 11 microm) as determined by flow cytometry. This fraction was increased 150fold in relation to background levels before grape crushing. Maximum concentrations of culturable bacteria reached 485,000 colony forming units (cfu/m3), whereas 146,000 cfu of fungi and yeasts were detected per cubic meter of air. Culturable Gram-negative bacteria occurred only in small numbers (180 cfu/m3). In relation to the total number of airborne particles emitted, culturable microorganisms comprised 0.1% to 0.2%. As soon as grape crushing was stopped, particle concentrations decreased rapidly either due to passive settling or due to air currents in the occupational indoor environment reaching background levels.
Changes in aboveground plant species diversity as well as variations of environmental conditions ... more Changes in aboveground plant species diversity as well as variations of environmental conditions such as exposure of ecosystems to elevated concentrations of atmospheric carbon dioxide may lead to changes in metabolic activity, composition and diversity of belowground microbial communities, both bacterial and fungal. We examined soil samples taken from a biodiversity x CO2 grassland experiment where replicate plots harboring 5, 12, or 31 different plant species had been exposed to ambient or elevated (600 ppm) levels of carbon dioxide for 5 years. Analysis of soil bacterial communities in these plots by temporal temperature gradient gel electrophoresis (TTGE) showed that dominant soil bacterial populations varied only very little between different experimental treatments. These populations seem to be ubiquitous. Likewise, screening of samples on a high-resolution level by terminal restriction fragment length polymorphism (T-RFLP) showed that increased levels of carbon dioxide had no significant influence on both soil bacterial community composition (appearance and frequency of operational taxonomic units, OTUs) and on bacterial richness (total number of different OTUs). In contrast, differences in plant diversity levels had a significant effect on bacterial composition but no influence on bacterial richness. Regarding species level, several bacterial species were found only in specific plots and were related to elevated carbon dioxide or varying plant diversity levels. For example, analysis of T-RFLP showed that the occurrence of Salmonella typhimurium was significantly increased in plots exposed to elevated CO2 (P < 0.05). Plant diversity levels are affecting bacterial composition (bacterial types and their frequency of occurrence). Elevated carbon dioxide does not lead to quantitative alteration (bacterial richness), whereas plant diversity is responsible for qualitative changes (bacterial diversity).
Perspectives in Plant Ecology Evolution and Systematics - PERSPECT PLANT ECOL EVOL SYST, 2005
The influence of plant diversity on belowground ecosystem processes and feedbacks of the latter o... more The influence of plant diversity on belowground ecosystem processes and feedbacks of the latter on plant growth are still largely unexplored. A previous field experiment showed positive effects of plant diversity on diversity and activity of culturable soil bacteria. We examined soil carry-over effects of these experimental communities on subsequent plant growth and the development of soil microbial communities in pots. We inoculated sterile substrate with soil from the field experiment and then sowed three plant species - Dactylis glomerata, Plantago lanceolata and Trifolium pratense - as monocultures or 3-species mixtures into the pots. We measured the phytometers over a period of 14 months. Thereafter, we sampled the soil in 3-species mixtures to analyze microbial communities. The original plant species richness and number of functional groups had positive soil carry-over effects on phytometer germination. Furthermore, in mixtures, species richness also stimulated short-term biom...
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fluorescence kinetics allows the quantification of effects on photosynthetic processes triggered by environmental
stress factors such as, e.g., the infection by fungal phytopathogens. The technique is non-invasive, rapid and well
suited for experimental field work.
Results: Healthy and Uromyces-infected plants of Euphorbia cyparissias were monitored directly in situ in the field
using rapid fluorescence kinetics. Non-infected healthy plants show a typical maximum value for the relative variable
fluorescence Fv/Fm of around 0.8 with occasional variation between the leaves from the plant top towards the base,
while infected plants exhibited a strong gradient to low values at the base. The photosynthetic performance index (PI)
showed a higher heterogeneity within the leaves in both plant types.
Conclusions: The non-invasive and rapid measurement of chlorophyll fluorescence induction allows characterizing
the photosynthetic capacity of healthy and infected plants and of parts of them directly in the field. The PI, is highly
sensitive not only concerning infection, but also towards other local environmental influences.
fluorescence kinetics allows the quantification of effects on photosynthetic processes triggered by environmental
stress factors such as, e.g., the infection by fungal phytopathogens. The technique is non-invasive, rapid and well
suited for experimental field work.
Results: Healthy and Uromyces-infected plants of Euphorbia cyparissias were monitored directly in situ in the field
using rapid fluorescence kinetics. Non-infected healthy plants show a typical maximum value for the relative variable
fluorescence Fv/Fm of around 0.8 with occasional variation between the leaves from the plant top towards the base,
while infected plants exhibited a strong gradient to low values at the base. The photosynthetic performance index (PI)
showed a higher heterogeneity within the leaves in both plant types.
Conclusions: The non-invasive and rapid measurement of chlorophyll fluorescence induction allows characterizing
the photosynthetic capacity of healthy and infected plants and of parts of them directly in the field. The PI, is highly
sensitive not only concerning infection, but also towards other local environmental influences.