Date of Award

2011

Degree Type

Thesis

Degree Name

Bachelor of Science (Environmental Management) Honours

School

School of Natural Sciences

Faculty

Computing, Health and Science.

First Advisor

Professor W.D. Stock

Second Advisor

Dr. S. M. Prober

Third Advisor

Associate Professor R. H. Froend

Abstract

The adaptive capacity of plant species will be important for increasing their resilience in a changing climate. By 2070, a change in rainfall of +10 to -40 % of current mean annual rainfall and warming of between +2 to +5 ˚C in south-west Western Australia, is predicted. Plant species may cope with changing climatic characteristics through natural selection or phenotypic plasticity responses. Greater ecotypic variation in traits between stands of a single species may reduce its vulnerability in a changing climate as there is a greater selection of traits to increase fitness. Phenotypic plasticity has been highlighted as a mechanism to potentially enhance resistance and resilience in a changing climate in the short-term. Given that the Mediterranean region of the south-west of Western Australia is considered to be the most vulnerable to contraction of all Mediterranean systems under predicted climate change scenarios, the region is a priority area for research into climate resilience and adaptive ecotypic variation in plant species. This project examined differences in morphological and physiological traits between nine stands of the widespread species E. loxophleba ssp. lissophloia L.A.S. Johnson & K.D. Hill (Smooth-barked York Gum) across a climate gradient in south-western Australia. Morphological and physiological traits known to promote efficient water use and drought tolerance were compared across its natural range (450 km from W to E), with samples of the same provenances also grown in a common garden (plantation) which receives higher long-term average annual rainfall. Ten trees per natural stand and per provenance were selected for sampling. Traits measured were total leaf length, maximum leaf width, the ratio of leaf length to leaf width, area per leaf, dry mass, specific leaf area, leaf nitrogen, carbon and nitrogen isotope ratios, instantaneous water use efficiency, maximum photosynthetic and transpiration rate and wood density. The eastern end of the gradient tended to have lower long-term average rainfall and higher long-term average temperatures than the sites further west. However, in the twelve months prior to sampling (01/06/2010 to 31/05/2011) rainfall patterns were anomalous and sites to the west of the gradient received below average rainfall. This meant that the long-term rainfall gradient was actually inverted when considering annual rainfall in the twelve months prior to sampling. The natural stands along the climate gradient and the plantation were similar in their soil characteristics and biotic structure. Results showed significant differences (one-way ANOVA) between the nine natural stands along the climate gradient for all of the traits measured, with the exception of wood density. This showed the high ecotypic variation present within the widespread species in both foliar morphological and physiological traits measured. However, there was no single, major climatic variable which was the primary cause of variation of all the traits, as determined by linear regression analysis. Comparisons of the natural versus planted stands showed high phenotypic plasticity responses in the physiological traits to prevailing climatic conditions, which should allow the species to cope with climate changes of a limited scale over the short-term. Morphological leaf traits showed a more conservative response, although the high ecotypic variation between stands suggests there is variation to facilitate change if given sufficient time. In conclusion, some adaptive capacity of traits relating to drought tolerance and water conservation has been shown in a single species. Despite the ability to cope with a changing climate afforded by phenotypic responses and ecotypic variation within a species, the necessity of mitigating climate change remains paramount.

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