Doctoral defense by Duo Chen

Performance of alien and native species in plant-plant and plant-soil interactions

Human activities have actively facilitated the expansion and establishment of a multitude of species beyond their native ranges. The continued increase in the number of these alien species poses a huge challenge to global biotic homogenization. Alarmingly, some alien species can become invasive, rapidly spreading and becoming dominant within their naturalized ranges, often at the expense of native species diversity. In invaded ecosystems, the coexistence of multiple alien species is a common occurrence that can facilitate the subsequent establishment of additional alien species (i.e. invasion meltdown hypothesis). Consequently, the complex interactions between species become more intricate, intriguing, and important to understand.

Towards the end of the last century, the theoretical framework of plant-soil interactions was proposed, paving the way for studies that focus on the effects of the belowground components of a plant’s environment on growth and competition. When it comes to alien plant species, their performance in naturalized ranges are jointly shaped by both the species they grow with and the soil they grow on. Despite advancements in this field, many questions remain as to how multiple characteristics of the plant species and soil environment interact to influence invasion success.

My thesis reveals that the performance of alien plant species is constrained by the diversity of recipient communities, the historical origins (alien or native) of their competitors, and plant-soil interaction processes. The dominance of some alien plants, as well as the positive feedbacks between invaders that are mediated by soil legacy, can be reduced by the presence of more diverse communities. However, co-occurrence of other alien species and soil-legacy spatial heterogeneity can still relatively favor the establishment of subsequent alien plants. My thesis highlights the importance of combining both plant-plant and plant-soil interactions in understanding the coexistence of alien and native plant species.