DYNAMIC OF BACTERIAL COMMUNITY COLONIZATION IN HIGH-ALTITUDE MOUNTAIN ENVIRONMENTS
Tesi di Dottorato
Data di Pubblicazione:
2014
Citazione:
DYNAMIC OF BACTERIAL COMMUNITY COLONIZATION IN HIGH-ALTITUDE MOUNTAIN ENVIRONMENTS / S. Ciccazzo ; tutor: D. Daffonchio ; coordinatore: D. Daffonchio. DIPARTIMENTO DI SCIENZE PER GLI ALIMENTI, LA NUTRIZIONE E L'AMBIENTE, 2014 Jan 27. 26. ciclo, Anno Accademico 2013. [10.13130/ciccazzo-sonia_phd2014-01-27].
Abstract:
Glacier forelands after glacier retreat are composed of harsh environmental niches characterized by severe climatic regimes and barren substrate with low total carbon and nitrogen content. Moraines represent ideal sites to study primary succession because glacier retreat releases an incoherent mineral substrate, where the primary succession and plant community establishment are key events in soil formation and fertilization. The underlying mechanisms driving this ecological succession remain still to be deepened. The physical and biogeochemical weathering processes provide soluble plant nutrient elements and when the plant colonization on parent materials occurs, the development of glacier foreland into fertile soils starts through rhizodeposition, exudation of nutritive substances, and decaying biomass. In these conditions, pioneer plants can select rhizosphere microbial communities able to promote plant growth thanks to the interactions with the system nutrient cycling. Moreover the rhizosphere community importantly contributes to the ecosystem functioning and carbon sequestration.
Main purposes of this study were: i) to characterize bacterial communities involved in soil neo-genesis processes under the environmental harsh condition and nutrient scarcity typical of high mountain moraines; ii) to assess the diversity, structure and role of bacterial communities associated to pioneer plant grown in a deglaciated alpine environment.
We studied first the Lobuche glacier moraines (Mount Everest area, Khumbu Valley, Nepal, about 5100 m a.s.l.), where we identified environmental niches characterized by different stages of biotic colonization, from bare mineral substrate to complex biological soil crusts (BSC). Seven sites of mineral proto-soil covered by BSC evidenced the ongoing soil development. The sites differed in several environmental parameters which could indicate different soil quality and developmental stages. Automated ribosomal intergenic spacer analysis (ARISA) showed distinctive bacterial community per each site and differences between the BSC and the below mineral substrate within the same site.
The second studied site was the Weisskugel glacier foreland in the upper Matsch valley within the upper Vinschgau Valley (South Tyrol). Upper Matsch valley showed a wide range of ecosystems: grasslands, bogs and poor fens, vertical rocky walls colonized by lichens, rocky glaciers, isolated pioneer plants, loosely organized floristic proto-communities, transition and mature grassland stages. The study area is below a glacier foreland at 2400 m a.s.l. The vegetation colonization was evolved since 1840 when the Matschter glacier began to retreat. The bacterial communities associated to different environmental matrices i.e. rock surfaces, proto-soils, riparian sediments, lichen thalli, and water springs biofilms were investigated by three molecular techniques with different taxonomic resolutions: denaturing gradient gel electrophoresis (DGGE), length heterogeneity-PCR (LH-PCR), and ARISA. Bacterial communities were mainly composed of Acidobacteria, Proteobacteria, and Cyanobacteria but variations occurred among the sites. Proteobacteria were more represented in sediments, biofilms, and lichens whereas Acidobacteria were mostly found in proto-soils and Cyanobacteria on rocks. Firmicutes and Bacteroidetes were mainly found in biofilms. UniFrac P values confirmed a significant difference among different matrices. Significant differences (P < 0.001) in beta diversity were observed at the genus–species level, except for lichens and rocks which showed a more similar community structure, while two distinct bacterial communities between lichens and rocks were found at deep taxonomic resolution.
In the same alpine ecosystem we investiga
Tipologia IRIS:
Tesi di dottorato
Keywords:
microbiology ; bacterial communities ; rhizosphere ; mountain environment ; nifH gene ; pyrosequencing
Elenco autori:
S. Ciccazzo
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