RA2 THESIS: Physiological responses to drought ...

Physiological responses of three native plants to drought and heatwave

June 2024

Rhodes G. 2024. Physiological responses of three native plants to drought and heatwave. Unpublished Master's thesis, University of Auckland, ResearchSpace@Auckland. 101 p.

ABSTRACT

Climate change in Aotearoa has predicted an increase in temperatures alongside turbulent weather patterns such as altered rainfall and increased severity and frequency of extreme weather events. This poses a significant threat to Aotearoa’s biodiversity particularly those that are already at risk of extinction. This study aimed to investigate the physiological responses of kauri (Agathis australis), rātā Moehau (Metrosideros bartlettii) and kahikā (Metrosideros excelsa) to simulated future climates by imposing a heatwave and drought in a glasshouse experiment. The study was designed in collaboration with Ngāti Kuri located in Te Rerenga Wairua, and the natural range of the critically endangered taonga species rātā Moehau. Treatments included a three day heatwave event, a 12 week drought reducing soil moisture content by 50%, and a seaweed fertiliser treatment to investigate whether the seaweed could help the plants resist the stress of the heatwave, drought, or combined heatwave and drought. The variables measured throughout the experiment included: leaf wilt score, leaf thickness, stomatal conductance, specific leaf area, leaf photographs, foliar nutrient concentrations, and foliar chlorophyll content. The experiment had surprising results when myrtle rust (Austropuccinia psidii) unexpectedly infected several of the Metrosideros plants. The infected plants experiencing heat and drought stress had higher susceptibility therefore an increased infection rate compared to control treatments. Kauri exhibited drought tolerance strategies through low stomatal conductance values, however rātā Moehau and kahikā had a lack of significant difference, making the interpretation of treatment effects difficult to detect. There was also no evidence to suggest that seaweed treatment had a significant effect on aiding plants through heat and water stress. Overall, the results provide preliminary physiological information on rātā Moehau where this data has previously been non-existent. The discovery of myrtle rust susceptibility on rātā Moehau in future climate simulations will also help advise Ngāti Kuri’s management plan working towards the future protection and restoration of this taonga species.