Showing papers by "Roland Psenner published in 2004"

Large-scale environmental controls on microbial biofilms in high-alpine streams

Abstract: . Glaciers are highly responsive to global warming and important agents of landscape heterogeneity. While it is well established that glacial ablation and snowmelt regulate stream discharge, linkage among streams and streamwater geochemistry, the controls of these factors on stream microbial biofilms remain insufficiently understood. We investigated glacial (metakryal, hypokryal), groundwater-fed (krenal) and snow-fed (rhithral) streams - all of them representative for alpine stream networks - and present evidence that these hydrologic and hydrogeochemical factors differentially affect sediment microbial biofilms. Average microbial biomass and bacterial carbon production were low in the glacial streams, whereas bacterial cell size, biomass, and carbon production were higher in the tributaries, most notably in the krenal stream. Whole-cell in situ fluorescence hybridization revealed reduced detection rates of the Eubacteria and higher abundance of α-Proteobacteria in the glacial stream, a pattern that most probably reflects the trophic status of this ecosystem. Our data suggest low flow during the onset of snowmelt and autumn as a short period (hot moment) of favorable environmental conditions with pulsed inputs of allochthonous nitrate and dissolved organic carbon, and with disproportionately high microbial growth. Tributaries are relatively more constant and favorable environments than kryal streams, and serve as possible sources of microbes and organic matter to the main glacial channel during periods (e.g., snowmelt) of elevated hydrologic linkage among streams. Ice and snow dynamics - and their impact on the amount and composition of dissolved organic matter - have a crucial impact on stream biofilms, and we thus need to consider microbes and critical hydrological episodes in future models of alpine stream communities.

Tools for discrimination and analysis of lake bacterioplankton subgroups measured by flow cytometry in a high-resolution depth profile

Abstract: A 24 m deep mesotrophic lake was sampled at 25 cm depth intervals throughout the whole water column for flow cytometric analysis of bacterioplankton, with the object of (1) assessing the suitability of image analysis algorithms to objectively discriminate bacterial subgroups in natural samples; (2) testing 2 models to evaluate the effect of changes in signal intensity versus changes in the relative abundance of the individual subgroups on bulk cell properties of the bacterial commu- nity; and (3) to examine the suitability of a numerical index for quantifying small-scale spatial vari- ability in cell abundance. Within the heterotrophic bacterial community, 5 subgroups were detected by image analysis of DAPI fluorescence versus side scatter (SSC) histograms. On average for the whole profile, 91% (range: 86 to 94%) of all measured bacteria belonged to the 5 subgroups. Along the depth profile, abundances within these subgroups showed trends which were different from that for the bacterial community as a whole. The comparison of the 2 numerical models suggested that shifts in average DAPI and SSC signals of the whole community are better explained by changes in relative abundance within individual subgroups rather than by signal shifts within individual subgroups. Spatial variability in cell abundance for most of the heterotrophic bacterioplankton subgroups was highest in the upper 4 m of the water column, corresponding to the zone of turbulent mixing, and between 9 and 12 m, at the depth of maximum picocyanobacterial abundance. Our results show that flow cytometry in combination with image analysis of DAPI-SSC histograms at the level of bacterial subgroups allow objective assessment of the structure of the bacterial community and underpin potential sources of small-scale variability in bacterioplankton distribution.

Microbial activity and phylogeny in ice cores retrieved from Lake Paula, a newly detected freshwater lake in Antarctica

Abstract: A permanent ice covered water body, called Lake Paula, was detected in Patriot Hills in the West Antarctic and sampled for the first time ever for microbial life. The ice sheet measured approximately 2,5m thickness and the water body has a depth of about 10m. The lake is situated near a moraine which partly ablates from snow and provides meltwater from the slopes to the lake during austral summer. These running waters which are kept liquid by the heating up of the dark soil are penetrating the lower ice cover and thus softening up the lakeside part if the ice core. It is inoculated by nutrients, active microbes and diatoms of terrestrial origin. A distinct gradient concerning bacterial numbers, biomass and production which is 10 fold at the ice-water interface compared to the exposed part is observable. Temperature sensitivity of the embedded microbes reflect the gradient as well: Bacteria isolated from the upper part showed growth optima at 10°C, the lower part at 25°C, phylogenetic properties done by 16s rDNA reveal distinct communities depending on their vertical position, some clones are similar to those retrieved in Lake Vostok ice cores. These results offer the conclusion that even in this harsh environment like the Antarctic continent a dynamic system like microbial ice aggregates can be sustained as long as the supply of liquid water which is essential for an active bacterial metabolism is provided at least for a small time frame.

Regional hydrology controls stream microbial biofilms: evidence from a glacial catchment

Abstract: Glaciers are highly responsive to global warming and important agents of landscape heterogeneity. While it is well established that glacial ablation and snowmelt regulate stream discharge, linkage among streams and streamwater hydrogeochemistry, the controls of these factors on stream microbial biofilms remain insufficiently understood. We investigated glacial (metakryal, hypokryal), groundwater-fed (krenal) and snow-fed (rhithral) streams ? all of them representative for alpine stream networks ? and present evidence that these hydrologic and hydrogeochemical factors differentially affect sediment microbial biofilms. Average microbial biomass and bacterial carbon production were low in the glacial streams, whereas bacterial cell size, biomass, and carbon production were higher in the tributaries, most notably in the krenal stream. Whole-cell in situ fluorescence hybridization revealed reduced detection rates of the Eubacteria and higher abundance of ?-Proteobacteria in the glacial stream, a pattern that most probably reflects the trophic status of this ecosystem. Our data suggest low flow during the onset of snowmelt and autumn as a short period (hot moment) of favorable environmental conditions with pulsed inputs of allochthonous nitrate and dissolved organic carbon, and with disproportional high microbial growth. Krenal and rhithral streams with more constant and favorable environments serve as possible sources of microbes and organic matter to the main glacial channel during periods (e.g. snowmelt) of elevated hydrologic linkage among streams. Ice and snow dynamics have a crucial impact on microbial biofilms, and we thus need better understanding of the microbial ecology and enhanced consideration of critical hydrological episodes in future models predicting alpine stream communities.