Many plant species are responding to global warming by expanding and shifting their ecological ranges to higher latitudes and altitudes. Such intracontinental plant range expansion is changing the composition of plant communities in the recipient habitats, which can cascade to other trophic levels and may consequently alter ecosystem functioning. Previous studies have shown that cross-continental exotic plants can alter the composition of soil microbial communities in a way that modifies the functioning of native ecosystems at local scales (e.g. nutrient cycling). In some cases, exotic plants benefit from accelerated nutrient mineralization rates and can become locally dominant over native species. It remains unclear, however, how the introductions through intracontinental plant range expansion will alter the composition and the functioning of soil communities in the new range. Here, we performed a greenhouse experiment to compare rhizosphere community assembly and functioning of range-expanding and related native plants in novel soils and soils that had been colonized previously by the plants. We sampled rhizosphere soil during plant development and analyzed bacterial rhizosphere community composition using high-throughput sequencing. To assess the functional capability of rhizosphere microbial communities, we measured carbon mineralization after adding a range of organic substrates and the activity of extracellular enzymes.
Our experimental design enabled us to assess the ability of native and range-expanding plant species to accumulate bacterial taxa in the rhizosphere over time. We show that range-expanding plant species and related natives develop similar bacterial rhizosphere communities when grown in the same novel soil communities. However, when the different plant species were grown in soils coming from field localities where these plants were already present, we observed that the rhizosphere communities were different at the start and remained different during plant growth. Additionally, we show that community-level functioning of rhizosphere communities changed significantly over time during plant development. However, the origin of the plant species did not affect carbon mineralization and enzyme activity.
Overall, these results provide a first insight into climate change effects on soil communities and their functions through plant-soil interactions. We conclude that range shifting plant species may change the composition of novel soil communities equally strong as related natives. However, when grown in soil communities that had longer shared history with the plant species studied, plant origin may influence rhizosphere community composition differently. Interestingly, these changes in soil microbial community composition did not influence general ecosystem processes.