Predicting which alien species will become invasive is key to mitigating their impact. It has been suggested that plant-soil feedbacks (PSF) between invasive plant species and soil microbial communities in the invaded range is one factor that can determine whether an alien plant species becomes invasive. Positive PSF (the alien plant species experiences enhanced performance due to soil microbial communities in the invaded range) could promote alien plant invasion but negative PSF (the alien plant species experienced reduced performance due to soil microbial communities in the invaded range) could help their control. However, a framework to predict which alien species will experience positive PSF, and under what conditions, is lacking. Such a framework is needed to provide a foundation for applied research on the impact of plant invasions on native plant communities, and how PSF knowledge might be used in ecosystem restoration worldwide (targeting EU Regulation 1143/2014 on Invasive Alien Species and Goal 15 of the UN Sustainable Development Goals).
I hypothesized that close relatedness of invasive with native plant species would be one factor that could help predict the outcome of PSF for invasions, but that whether these outcomes promoted or prevented invasion would depend on local context. Focusing on variation in nutrient availability (as context), I aimed to address three key research objectives: 1) quantify the strength of PSF under differing nutrient conditions; 2) characterise mutualistic associations in the roots; and 3) characterise the soil microbial communities they cultivate.
Due to COVID-19 and subsequent offer of a permanent position, the duration of the project was only 4 months and work was entirely desk-based. Consequently, I sought to examine the major themes of the project from a theoretical perspective and/or using existing data. Specifically, I aimed to:
1) Identify whether knowledge of species relatedness could help predict the outcome of PSF;
2) Explore other factors that influence the degree to which PSF outcomes could be predicted;
3) Examine the role of local context in influencing the outcome of PSF.
This work is still ongoing and conclusions so far are that:
1) Knowledge of species relatedness can only predict the outcome of PSF when species are either closely related or belong to key plant taxa known to show strong responses to soil mutualists.
2) PSF outcomes are highly variable within and among studies, and it remains unclear what drives this very high variability.
