Effects of exotic plant species on soil and litter microbial communities

Invasions by exotic species are becoming of increased importance, as they are now considered a component of global change. Exotic plants that successfully establish in and may even replace native communities are known to alter important soil properties, such as nitrogen concentrations and turnover and soil organic matter, yet their effect on microbial communities in soil, which can be directly linked to these soil characteristics, is unknown. I report here field and greenhouse studies that were designed to explore the relationship between plants and soil microbial communities in a system where two exotic understory plants (Berberis thunbergii and Microstegium vimineum ) have become recently established.;The activity of litter microbiota was followed during the decomposition of litter from 4 plant species in two locations, an exotic invaded area and an area dominated by native shrubs (Vaccinium spp.). Differences in individual enzyme activities showed a strong effect of the litter chemistry on the activity of the decomposing community, however, multivariate analysis that incorporated all activities simultaneously, revealed differences between the two locations studied.;The diversity and function of microbial communities was also studied, in both field and greenhouse experiments. In both studies, three different methods (phospholipid fatty acid profiles, enzyme activities and respiratory responses to substrates) showed that microbial communities under the two exotic species differ significantly from microbial communities found under native blueberries. In the field study differences were observed in both bulk and rhizosphere soils, indicating a long term effect of the exotic species in soil not in immediate contact with their roots. In the greenhouse experiment plants were grown on the same mineral soils taken from a non-invaded stand, therefore, the observed changes in microbial communities could be linked directly to the presence of plants. Moreover, I observed significant alterations in soil pH and nitrogen dynamics in the soil under the two exotic species.;Overall, the study demonstrates that established exotic species can significantly alter soil and litter-decomposing microbial communities. These changes are a potential mechanism which may explain the observed differences in soil and ecosystem level properties between invaded and non-invaded stands.