Understanding the response of soil microbial communities to various environmental stresses is of current interest, because of their pivotal role in nutrient cycling, soil organic matter mineralization and influence on plant growth. Determining the affect of several biotic and abiotic factors on soil microbial communities is the overall objective of the study. The specific goals are to determine 1) the response of microbial communities to water deficit in soil and 2) how the presence of a rich biotic community determines the direction of microbial community development in cultures. Both goals are novel and unique contributions to understanding microbial ecology in soil. Dynamics in water potentials due to drying and rewetting of soil impose significant physiological challenges to soil microorganisms. To cope with these fluctuations, many microorganisms alter the chemistry and concentration of their cytoplasmic contents. The aim of this research is to understand how the microbial biomass and their cytoplasm change in response to water potential deficits under in situ soil conditions. To address this objective we characterized intracellular and extracellular metabolites in moist, dry and salt stressed soils. Our results provided the first direct evidence that microbial communities in soil in situ utilize sugars and sugar alcohols to cope with low water potential. While the cultivation and isolation of microorganisms is essential to completely explore their physiology and ecology, 99% of soil microbes resist growing in cultures. Presence of very unnatural conditions in the culture plates was considered as main reason for low cultivability. Thus, a culture-based study was conducted whereby microorganisms were grown in association with their native habitat with an objective of mimicking native conditions to promote the growth of previously uncultivated microorganisms. Moreover, the importance of biotic communities (microbe-microbe) and abiotic soil effects were assessed on bacterial growth. Our results strongly indicate that the presence of living microbial community in the vicinity of the target culture resulted in the cultivation of novel members of rare bacterial taxa from phyla Verrucomicrobia, Bacteroidetes, Proteobacteria, and Planctomycetes. These results emphasize the need to develop new culturing methods to tap the hidden microbial potential for emerging anthropogenic needs.

The relative importance of abiotic versus biotic top-down factors on structuring tundra plant communities is debated. With climate change already strongly affecting the tundra ecosystem, understanding which factors will prevail is vital. Tundra plant communities are presumed to be predominantly structured by their abiotic conditions yet grazing by reindeer (Rangifer tarandus) has a major effect on composition and diversity. It is increasingly recognized, however, that these factors cannot be considered in isolation. Here, I aim to test the relative and interactive effect of abiotic and top- down factors on vegetation structure in the Swedish mountain tundra. Using direct measurements of reindeer grazing via tri-axial accelerometers (from two summers, 2019 and 2020) coupled with remotely-gathered data on landscape features, I examine how species richness and coverage of vascular plants, bryophytes and lichens (sampled in 2022) are driven by grazing duration and abiotic conditions. Abiotic factors, specifically aspect and soil wetness, prevailed as the dominant drivers of local vegetation patterns. Clear interactions between factors were also observed. Reindeer grazing duration had predictable but weak effects on richness, with responses predominantly observed on south-facing slopes. Additionally, soil wetness interacted with grazing duration, with wetter areas grazed far less. These results demonstrate the importance of considering interactions between abiotic and biotic factors, providing a better understanding of how tundra plant communities in northern Sweden might change under future climate change or different grazing regimes. The observed interactions imply divergence in vulnerability between slopes and the potential for effects of herbivory to be altered under future hydrological conditions. I emphasize that future studies should continue to disentangle these relationships.