Master of Science (MSc)
Faculty of Science
Dr. Kevin Stevens
Dr. Mihai Costea
Virginia Mallow (Sida hermaphrodita) is a perennial herb of the Malvaceae family that is native to riparian habitats in northeastern North America. Throughout most of its geographical distribution however, it is considered threatened and only two populations are known from Canada. The biology and ecology of S. hermaphrodita are still poorly understood and although few studies have been performed to determine the factors that contribute to the species rarity, it is considered threatened potentially due to the loss of habitat caused by exotic European Common reed (Phragmites australis subsp. australis) invasion. Allelopathic and phytotoxic conditioning of soils to inhibit native species are mechanisms that have been proposed to explain the invasion success of P. australis. To quantify the interaction between the two species and assess the capacity for P. australis to inhibit S. hermaphrodita performance through belowground soil modifications, a series of field vegetation surveys were conducted at the Taquanyah Conservation Area during the growing seasons of 2016, 2017, and 2018. Field performance findings suggested that proximity to P. australis had no significant effect on S. hermaphrodita seedling mortality or seedling root arbuscular mycorrhizal colonization. A supplementary greenhouse study was also conducted to examine plant performance and mycorrhizal colonization of both species in soils that correspond to different soil-vegetation levels ranging between pure stands of S. hermaphrodita to pure stands of P. australis in order to determine the potential for P. australis to allelopathically modify soils making them inhospitable for native species. The results provided no evidence to support previous soil conditioning reports since performance and arbuscular mycorrhizal colonization of both species were inversely promoted in their competitor’s soil. Soil nutrient analysis coupled with the plant performance findings suggested that P. australis may not be as strictly competitive as previously believed since evidence of a belowground facilitative interaction between S. hermaphrodita and P. australis has been observed. Based on the results concluding that belowground conditions did not exclude native species, we believe aboveground competition for light is not only the main factor contributing to S. hermaphrodita’s limited distribution where it occurs with P. australis, but also key to the invasion success of P. australis. Future research and management treatments focussed on disrupting P. australis’ competitive exclusion of light would be beneficial to the recovery of endangered species like S. hermaphrodita.
Mulholland, Samantha N., "Competition or facilitation: Examination of interactions between endangered Sida hermaphrodita and invasive Phragmites australis" (2019). Theses and Dissertations (Comprehensive). 2223.
Available for download on Tuesday, September 29, 2020