Genetic adaptation and phenotypic plasticity influence trait expression under heatwave and water deficit conditions in the foundation tree, Corymbia calophylla

Abstract

Climate change presents a major threat to forests globally, and is currently impacting forest carbon sequestration and contributing to increased tree mortality. Rising temperature, greater heatwave intensity and rainfall reductions associated with climate change are projected throughout many forested regions. Trees must respond to climate change through genetic adaptation, phenotypic plasticity or a combination of these processes, if not risk local extinction. Identifying the capacity for trees to respond through adaptive capacity to high temperature and water deficit conditions may help us better understand and predict forest resilience and function under climate change. Genetic adaptation is a shift in the genotypic composition of a population caused by environmental change typically over multiple generations. Phenotypic plasticity is the differential expression of a phenotype in response to variable environments by a genotype potentially providing a rapid response from minutes, hours, days to years. A genotype-by-environment interaction is the differential expression of plant traits by multiple genotypes across contrasting environments. These processes can be identified by measuring traits indicative of plant performance and survival for multiple genotypes in common garden experiments with contrasting environments and reciprocal plantings. The main aim of this thesis was to identify genetic adaptation, phenotypic plasticity and genotype-by-environment interactions influencing important temperature and drought-associated traits in the south west Australian foundation tree species, Corymbia calophylla (R. Br.) K.D. Hill & L.A.S. Johnson (Eucalyptus sensu lato; family Myrtaceae) under mild temperature and water availability conditions, and also stress-inducing heatwave and water deficit conditions. This was achieved using three common garden experiments involving water or temperature manipulation with multiple populations grown reciprocally across contrasting environments. This study contributes to the understanding of forest responses to climate change-associated shifts in temperature and rainfall, and critically, it provides important information on adaptive capacity to climate change provided through genetic adaptation and phenotypic plasticity.

Date of Award	2020
Original language	English