|The aim of this PhD research was to study multi-element composition in wetland plants from contrasting habitats, including hot springs, temporary wetlands, and metal-rich areas. Triglochin maritima L. (seaside arrowgrass) was chosen for the study because this species is common in alkaline/saline soils and is adapted to diverse habitats. Eleocharis rostellata, Juncus balticus, Salix exigua, S. boothii, and S. wolfii were also included in the study. Field studies and greenhouse experiments were conducted to study the multi-element composition in plants. In the greenhouse experiment the effects of temperature and soil biota on multielement uptake in T. maritima were studied. Root-zone soils and plant samples were analyzed for 32 - 50 elements using inductively coupled plasma OES/MS spectrometry. The expected outcomes from this research were: 1) the development of multi-element fingerprints for T. maritima and other plant species from contrasting habitats, and 2) a better understanding of the effects of temperature and soil biota on multi-element uptake in T. maritima. Habitat specific element concentration patterns in T. maritima were observed; concentrations of Mn, Li, and B were high in plants from hot spring influenced wetlands, whereas Ca, P, Mg, Fe, Sr, Ba, Ti, and Cu were higher in the plants of temporary wetlands. J. balticus and Salix species from mine impacted and uncontaminated sites revealed distinct differences in multi-element fingerprints. J. balticus showed high concentrations of S, K, Mn, Fe, Cu, Al, As, and Cd at contaminated sites compared to un-contaminated sites. Multi-element fingerprints of Salix species showed that S. boothii had higher concentrations of Mn, Fe, Al, and Ti compared to S. exigua and S. wolfii. To our knowledge for the first time the association of mycorrhizal fungus in T. maritima was confirmed, and significant effects of temperature on element concentrations, contents, and their translocation in plants were observed. Generally, the distribution of the total contents of P, Na, Mn, B, Cu, Mo, Li, Sr, Ti, and Cs in both roots and leaves were lower at 40 °C compared to 20 and 30 °C, but their distribution and translocation from root to leaves were higher at 40°C. Even though the biological and physiological functions of Li, Sr, Ba, Rb, and Ti in plants are not fully understood, these elements were substantially taken up by T. maritima, and significant positive correlations of these elements were found with elements that have known biological functions. Overall, concentrations of Ca, P, Mg, Mn, B, Sr, and Ba in T. maritima showed variation due to differences in habitats, temperature, and experimental growing conditions (greenhouse and field condition). Concentration patterns of Na, K, and Zn were species specific and affected by temperature. Li concentrations varied due to habitat differences, growth conditions, and species differences. Future research directions could include: 1) identification of the fungal species associated with T. maritima and studies to elucidate their possible role in survival of T. maritima in the elevated temperature of hot springs, 2) the effects of soil factors, such as salinity and 3) seasonal variation in uptake and translocation, particularly for the less studied elements with yet unrecognized but potential biological functions in plants.