Biochemical Responses of Arctic Soil Communities to Anthropogenic Stress
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We are living in the era of climate change which becomes more complicated whenever some new environmental issue emerges only to get linked with this already existing challenge. Engineered nanoparticle (NP) contamination is of such issue which may become a major environmental problem under some circumstances in the decades to come. NP-based technologies have proven themselves useful and have the potential for greater promise, but they could become more than a nuisance. Unfortunately, very limited information is available on the environmental impacts of NPs in general and soil in particular. In this thesis, I examined the impact of NPs on soil microbial communities and by trying to avoid the presence of existing NPs I used soil from arctic regions. To examine the effect of another anthropogenic change on the same soil, I investigated the impacts of freeze-thaw cycles (FTCs). This thesis demonstrated that Ag-NPs and Cu-NPs cause a shift in microbial communities. The use of culture-dependent and culture-independent assessment techniques for microbial communities inspired the development of a toxicity indicator. This tool assigned the highest toxicity index to Ag-NPs and a low toxicity to SiO2-NPs. Supporting in vitro studies confirmed that Bradyrhizobium canariense was particularly sensitive towards Ag-NPs. Further analysis showed that a mixture of Ag-, Cu-, and SiO2-NPs were toxic. FTCs were also a significant stress; they had a differential impact upon soil communities derived from different arctic sites. My results suggest that the impact of climate change at high latitudes may not be predictable. Finally, I used a FTC regime shown not have an impact on low arctic sites and compared two different concentrations of Ag-NPs and Ag-microparticles and validated the higher toxicity impact of Ag-NPs on both bacterial and fungal communities. Taken together, these findings represent an initial attempt to try to understand the impacts of two stresses attributable to human activities on arctic soils, soils that are crucial to the health of our planet.