Investigating the seed germination and phytoremediation potential of New Zealand native plants in metal contaminated soils
Thesis DisciplinePlant Biology
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
The unintentional accumulation of biologically, non-essential metals like cadmium (Cd) and arsenic (As) in New Zealand agricultural and urban/ industrial soils has become of some concern with regard their entry into our food chain. As conventional soil remediation technologies are often expensive and can have negative side-effects on the environment, phytoremediation is a promising “environmentally friendly” alternative with some existing successful applications in New Zealand. Additional benefits of using New Zealand native plants for phytoremediation projects include the provision of important ecological services as well as cultural and aesthetic values to the local community. The objective of this study was to determine the in-situ seed germination and seedling survivorship potential of New Zealand native plant species in Cd contaminated soils and investigate the presence (or absence) of physiological mechanisms conferring (or suppressing) tolerance to Cd or other metal contaminants. An in vitro seed germination bioassay exposing 16 New Zealand native plant species to aqueous Cd and As solutions indicated test species appeared to have varying tolerances to Cd and As with the Rock Lily (Arthropodium cirratum) and Kanuka (Kunzea ericoides) displaying the most tolerance and sensitivity respectively. Seeds of the Rock Lily germinated when exposed to 50mM L-1 solutions of Cd and As (~16% and ~13% respectively) while Kanuka seeds failed to germinate when exposed to Cd concentrations >0.25mM L-1. Germination rate and peroxidase activity results indicated responses differing in magnitude to Cd and As treatments therefore indicating species specific tolerances to Cd and/or As. Other test species showed a general negative dose-response trend with regard to germination rate. Ex situ seed germination bioassay data indicated germination rates in response to Cd treated soil media and a Cd containing field soil sample. All but one of the six test species germinated and grew in the field soil sample indicating that at current average Cd content, these species would be capable of germinating and growing in New Zealand agricultural and horticultural soils. Seedling heights, root length, total chlorophyll content and peroxidase activity were all generally inhibited by exposure to increasing Cd concentrations in the ex situ seedling survivorship bioassay. Average Rock Lily root tissue Cd content was 48.3mg Kg-1 compared to 227.5mg Kg-1 in Kanuka suggesting the Rock Lily’s tolerance may be conferred through the ability to exclude or reduce the absorption rate of Cd. On the contrary, Kanuka may lack these same physiological mechanisms as the species suffered from low germination rates and peroxidase activity when exposed to Cd treatments. Overall, study results suggest that tolerances to soil metal contaminants exist in New Zealand native plants with physiological de-toxification and avoidance mechanisms that confer successful in situ seed germination and seedling survival.