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Theses

Snow ecosystem, microbial community structure and function in artic snowpacks

Abstract : The Arctic seasonal snowpack can extend at times over a third of the Earth’s land surface. This chemically dynamic environment interacts with different environmental compartments such as the atmosphere, soil and meltwater, and thus, strongly influences the entire biosphere. During the last decades, snow has been recognized as a microbial reservoir. The ecology of snow microorganisms however remains poorly understood. The main goal of this thesis was to investigate the snow as a functional ecosystem; i.e. a community of living organisms in conjunction with the non--‐living component of their environment and interacting as a system. In order to do so, microbial community taxonomic and functional composition of snow samples from two arctic snowpack models: seasonal snow from terrestrial fresh water snowpack (Ny--‐Alesund, Svalbard) and sea ice snow cover (Nuuk, Greenland) was analyzed using high throughput sequencing technologies. The first objective addressed microbial community heterogeneity in relation with fluctuating environmental conditions. Snow microbial community composition was highly variable during spring season and depth. The relationship between microbial functions and environmental conditions supports the hypothesis that the snow microbial community interacts with the abiotic variability characteristic of their habitat. The second objective addressed snow community specificity; if the snowpack is a functional ecosystem, then the microbial communities inhabiting it should have specific features related to their adaptation to the conditions of this environment, despite variability. The comparison of functional distribution between snow and both remote (polar and non polar) and closely interacting environments provided evidence of snowpack microbial community specificity. The third objective focused on environmental selection, given that the existence of a specific snow microbial community implies that one or more selective processes occur in the snowpack. Comparing the distribution of microbial community structure and function as related to the source of the microorganisms in a sea ice snow cover revealed that snow microbial communities were largely influenced by, yet differed from their seeding sources in response to specific environmental conditions. Mechanistic approaches with model microorganisms in snow microcosms were developed during this thesis and, based on preliminary results, will help to determine colonization processes within snowpack. Finally, preliminary results in the first section of Chapter 4 also showed that a high variability exists between the microorganisms present within the snowpack, and those that are active. Although technical and conceptual issues remain, RNA based high throughput sequencing was evaluated as an encouraging tool to evaluate short--‐term responses of microbial communities to environmental fluctuations. While numerous questions remain about microbial activity and complex community interactions, the results from this thesis support the hypothesis that snow is a functional ecosystem.
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Submitted on : Friday, March 11, 2016 - 10:54:05 PM
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  • HAL Id : tel-01287177, version 1

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Lorrie Maccario. Snow ecosystem, microbial community structure and function in artic snowpacks. Other. Ecole Centrale de Lyon, 2015. English. ⟨NNT : 2015ECDL0021⟩. ⟨tel-01287177⟩

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