Impacts of non-native invertebrates and plants on polar soil systems.

Invasive non-native species are amongst the most serious threats to biodiversity at local and global scales. Due to their geographical remoteness, extreme conditions and lower levels of human activity, the Earth's polar regions have seen fewer invasions to date compared to temperate and tropical areas. However, increasing human activity in high latitude areas brings the risk of many more species introductions, while climate warming is reducing many of the abiotic barriers to species establishment. Polar ecosystems are particularly susceptible to the negative effects associated with invasive species due to their low native diversity, simple food chains and the availability of apparently vacant niches. To date, few studies have tested the effects of non-native species on soil properties in the typically nutrient-limited polar regions. Non-native arthropods and plants may introduce their novel microbiomes and fungal endophytes to a new environment, and this can lead to changes in organic matter decomposition and levels of bioavailable nutrients such as nitrogen. Decomposition rates may be increased further in synergy with climate warming, releasing locked up nutrients in addition to nutrient enrichment facilitated by invasive species. Enhanced nutrient availability and microbial activity may, in turn, create more favourable conditions for the establishment and, for some, the subsequent invasion of further non-native species, as well as potentially benefiting native arthropod and plant communities. This review characterises the interactions between invasive species and global change, highlighting current and predicted future impacts on soil health in polar ecosystems. In addition, we identify priority areas for further research to better understand these impacts and guide management practices.