39 research outputs found
A comparison of three-dimensional stress distribution and displacement of naso-maxillary complex on application of forces using quad-helix and nickel titanium palatal expander 2 (NPE2): a FEM study
Bacterial Communities Involved in Soil Formation and PlantEstablishment Triggered by Pyrite Bioweathering on ArcticMoraines
Abstract In arctic glacier moraines, bioweathering primed
by microbial iron oxidizers creates fertility gradients that
accelerate soil development and plant establishment. With
the aim of investigating the change of bacterial diversity in
a pyrite-weathered gradient, we analyzed the composition
of the bacterial communities involved in the process by
sequencing 16S rRNA gene libraries from different biological
soil crusts (BSC). Bacterial communities in three BSC
of different morphology, located within 1 m distance
downstream a pyritic conglomerate rock, were significantly
diverse. The glacier moraine surrounding the weathered site
showed wide phylogenetic diversity and high evenness with
15 represented bacterial classes, dominated by Alphaproteobacteria
and pioneer Cyanobacteria colonizers. The bioweathered
area showed the lowest diversity indexes and only nine
bacterial families, largely dominated by Acidobacteriaceae
and Acetobacteraceae typical of acidic environments, in
accordance with the low pH of the BSC. In the weathered
BSC, iron-oxidizing bacteria were cultivated, with counts
decreasing along with the increase of distance from the rock,
and nutrient release from the rock was revealed by
environmental scanning electron microscopy-energy dispersive
X-ray analyses. The vegetated area showed the presence
of Actinomycetales, Verrucomicrobiales, Gemmatimonadales,
Burkholderiales, and Rhizobiales, denoting a bacterial
community typical of developed soils and indicating that the
lithoid substrate of the bare moraine was here subjected to an
accelerated colonization, driven by iron-oxidizing activity
Microbial community changes along the Ecology Glacier ablation zone (King George Island, Antarctica)
Comparison of Soil Bacterial Diversity in Rotation and Monocropping Soil in Tobacco Growing Area in Yuxi, Yunnan, China*
Culturable bacteria community development in postglacial soils of Ecology Glacier, King George Island, Antarctica
Glacier forelands are excellent sites in which to study microbial succession because conditions change
rapidly in the emerging soil. Development of the bacterial community was studied along two transects on lateral
moraines of Ecology Glacier, King George Island, by culture-dependent and culture-independent approaches
(denaturating gradient gel electrophoresis, DGGE). Environmental conditions such as cryoturbation and soil
composition affected both abundance and phylogenetic diversity of bacterial communities. Microbiocenosis
structure along transect 1(severe cryoturbation) differed markedly from that along transect 2 (minor
cryoturbation). Soil physical and chemical factors changed along the chronosequence (time since exposure) and
influenced the taxonomic diversity of cultivated bacteria (CB), particularly along transect 2. Arthrobacter spp.
played a pioneer role, and were present in all soil samples, but were most abundant along transect 1. Cultivated
bacteria isolated from transect 2 were taxonomically more diverse than those cultivated from transect 1; those
from transect 1 tended to express a broader range of enzyme and assimilation activities. Our data suggest that
cryoturbation is a major factor in controlling bacterial community development in postglacial soils, shed light on
microbial succession in glacier forelands, and add a new parameter to models that describe succession
phenomena
Microbial community structure and ecology of subglacial sediments in two polythermal Svalbard glaciers characterized by epifluorescence microscopy and PLFA
Changes in fungal community structure in bulk soil and spinach rhizosphere soil after chemical fumigation as revealed by 18S rDNA PCR-DGGE
Abundances and potential activities of nitrogen cycling microbial communities along a chronosequence of a glacier forefield
Glacier forefields are ideal ecosystems to study the development of nutrient cycles as well as single turnover processes during soil development. In this study, we examined the ecology of the microbial nitrogen (N) cycle in bulk soil samples from a chronosequence of the Damma glacier, Switzerland. Major processes of the N cycle were reconstructed on the genetic as well as the potential enzyme activity level at sites of the chronosequence that have been ice-free for 10, 50, 70, 120 and 2000 years. In our study, we focused on N fixation, mineralization (chitinolysis and proteolysis), nitrification and denitrification. Our results suggest that mineralization, mainly the decomposition of deposited organic material, was the main driver for N turnover in initial soils, that is, ice-free for 10 years. Transient soils being ice-free for 50 and 70 years were characterized by a high abundance of N fixing microorganisms. In developed soils, ice-free for 120 and 2000 years, significant rates of nitrification and denitrification were measured. Surprisingly, copy numbers of the respective functional genes encoding the corresponding enzymes were already high in the initial phase of soil development. This clearly indicates that the genetic potential is not the driver for certain functional traits in the initial phase of soil formation but rather a well-balanced expression of the respective genes coding for selected functions