Biological invasion is a global phenomenon that has caused great damage to ecosystems as well as to the economy. Many factors have been found to be associated with and contributed to the success of invasive species. Phenotypic plasticity, the ability of a plant genotype to respond to different environmental conditions by producing different phenotypes, might play an important role in biological invasion, but more empirical studies are needed before a general pattern emerges that can be used in predicting the invasive potential of a species.
This dissertation describes studies that investigated the role of phenotypic plasticity in the success of invasive plants using three dandelion species (Taraxacum, Asteraceae) as model system. Taraxacum officinale is an aggressive weed, while T. laevigatum only has limited distribution in North America. T. kok-saghyz has been introduced as a potential crop, but its potential invasiveness is unknown. In three major experiments, I tested the hypothesis that the invasive T. officinale and non-invasive T. laevigatum will exhibit different phenotypic plasticity in germination, growth, and reproduction in various lab, greenhouse, and field environments. I also proposed that their responses in stressful and favorable conditions could be used to assess the invasive potential of T. kok-saghyz.
The results revealed complicated responses of the three species in various environments. The invasive T. officinale showed higher germination in high alternating temperature, and accumulated more biomass than the non-invasive T. laevigatum in favorable greenhouse conditions. Surprisingly, T. laevigatum germinated better than T. officinale in other stressful environments (dark, low water potential, long aging period), and also exhibited higher fecundity in favorable greenhouse conditions. In field experiments, however, the performance of T. officinale was overwhelmingly better than T. laevigatum, which suffered very high mortality and failed to survive for more than two growing seasons. These results suggest that T. officinale might benefit from its ability to grow, reproduce, and survive in various environments, while T. laevigatum relies on seed reproduction to maintain its population. With the exception of germination, the responses of T. kok-saghyz were more like T. officinale than T. laevigatum, which suggested that this species has some potential to behave as a weed.
This work demonstrated the importance of comparative study between invasive and non-invasive species across different environments, and showed complicated mechanisms underlying invasion success.