| Summary: | Biotic and abiotic characteristics shape the microbial communities in the soil environment. These characteristics vary both spatially and temporally, depending on variations in temperature, water availability and plant coverage, which on a larger scale are driven by topography, soil type, land use, vegetation and the ruling climate. In a sub-arctic climate, the seasonal fluctuations in temperature, precipitation and plant cover force the microbes in the top soil to adapt or decline. For many organisms trying to survive the cold winters, a nest can provide protection from the harsh environment. For example, the mound building wood ants, such as the Formica exsecta, selectively choose both the spot, and the building material for their nest mounds, in which they overwinter. These ants are also able to generate extra heat by using their lipid reserves during early spring, to secure the brood development. The higher and steadier temperature inside the nest is further enhanced by the decomposing process, intensified by the constant addition of organic plant material carried out by the ants, and the availability of nutrients. This creates a unique microclimate inside the nest mounds, in which the microbes can stay largely protected from the environmental drivers of the microbial communities in the surrounding top soil. I hypothesized, that the nest environment would promote the formation of unique bacterial and fungal communities in the nests, compared with the surrounding soil. I also hypothesized that the nest communities are stable in time, and that they would show less temporal than spatial variation. Furthermore, I expected to see nest-characteristic, temporally stable taxa, which could be identified as the core microbiome of the F. exsecta nests. However, to ensure a robust methodological approach, I first tested the combination of Next Generation Sequencing (NGS) and a classical community fingerprinting method, Terminal Restriction Fragment Length Polymorphism (T-RFLP). I sampled nests of the mound-building ant ...
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