The role of soil microbiota in the interaction between the invasive plant Lupinus polyphyllus and three native herbs

Abstract

Species invasions are a significant element of global change. There are several mechanisms in which invasive species dominate the natives in their invaded range. One of those mechanisms is plant-soil feedback. In my master’s thesis I assessed the role and importance of soil microbiota in the interactions between the herbaceous invader Lupinus polyphyllus (garden lupin) and three native herbs commonly found in human-affected habitats representing different attributes: Trifolium repens (white clover), Centaurea cyanus (cornflower) and Taraxacum spp. (dandelion). I evaluated the effects of competition and the presence of soil microbes by growing L. polyphyllus together with each of the three native plant species in a common garden pot experiment. A soil inoculum crafted from around lupin roots was used to introduce soil microbes into the sterilized substrate. The results of this study suggest that competition (the presence of L. polyphyllus) has an effect on the studied native herbs’ growth and these effects vary among species. The effects were not all negative, as T. repens grew more shoots when growing with L. polyphyllus and C. cyanus was unaffected. Taraxacum spp. however, showed a significant decrease, especially in root growth. Soil microbes associated with L. polyphyllus also affected the growth of the studied natives, but species responded to the microbe addition similarly, growing less roots. Also, in turn, the species L. polyphyllus was growing with affected its growth. The biomass of L. polyphyllus was negatively affected by the presence of C. cyanus. Lupinus polyphyllus nodule growth was tentatively affected by microbes and competition together, as with Taraxacum spp. the microbes seemed to affect the growth of the nodules negatively. I conclude that the benefits of mutualistic soil microbes may vary with the species the invader is competing with. I also suggest that the effects of soil microbes, both positive and negative, may differ in different competitional settings. Hopefully, these results can add to the knowledge of mechanisms of invasions, important in planning conservational efforts and screening for possible invaders.