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Response to SO2 exposure of crop species and important eucalyptus species in Australia

Wilson, Susan Ann (1993) Response to SO2 exposure of crop species and important eucalyptus species in Australia. PhD thesis, Murdoch University.

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The primary objective of this research was to investigate the impact of long-term exposure to SO2 on the growth and yield of major agricultural plant species and commercially important forest Eucalyptus species grown under Mediterranean climatic conditions in Australia; thereby providing the scientific criteria necessary for the development of air quality standards for sulphur dioxide (SO2) in Australia. There has been very little research on the response to SO2 of plants which grow in dry or Mediterranean climates; to date Australia has largely relied on overseas data to predict the impact of air pollutants on its agricultural and forestry industries. The vast majority of these data have been derived from studies on the effects of plants grown in cooler, moister climates. Vegetation grown in a Mediterranean climate, however, possesses certain biological features that enable success in such a climate; evidence suggests that the vegetations' response to SO2 may be different from that of other vegetation types. More particularly, as a most distinctive feature common to plants grown in Mediterranean climates is their drought stress resistance, it is possible that common mechanisms underlie the resistance of both drought stress and SO2 stress; this is explored at a theoretical level. As a consequence of biological differences, extrapolation from studies on plant species successful in cool, moist climates may be inappropriate in predicting the response to SO2 of Mediterranean climate vegetation.

The research was divided into two main areas. Firstly, the effects of long-term SO2 exposure on growth, yield and/or quality of the most important cereals, nitrogen-fixing pasture species and Eucalyptus tree species grown under Mediterranean climatic conditions in open-top chambers were studied. This resulted in a comprehensive documentation of the effects of SO2 on the most commercially important plants in Australia and the development of exposure-response models. Secondly, construction and analysis of a data base for all data derived in Australia was undertaken resulting in the establishment of generalised exposureresponse models to define the response to long-term SO2 exposure of agricultural species grown in a Mediterranean climate and the genus Eucalyptus. The data were derived from many experiments but represent a unique uniformity of sampling and exposure techniques. In all cases the most appropriate model to describe plant response to SO2 exposure was a regression between SO2 concentration and percentage yield change or the logarithm of percentage yield change; the models had the capacity to explain up to 75% of the variability in the data and were not improved by a number of transformations of either variable. The model limitations, conditions for application and areas highlighted by the study requiring further research are discussed.

The study provided several results which did not support the hypothesis that the genetic material, and therefore biological features, associated with the type of plants grown in Mediterranean regions of Australia would result in a response different to that of plants grown in other climatic regions. The findings suggested that as a group, agricultural plants adapted to water-limited conditions vary widely in their response to SO2 exposure and do not appear to differ in response from plants adapted to other climatic conditions. Therefore air quality standards developed overseas may be appropriate at a general level to protect agricultural plants. Eucalypts, however, appear to be amongst some of the most sensitive species to SO2 tested to date, world-wide and the transportation of overseas air quality standards would not be valid for their protection. It is postulated that this is, at least in part, attributable to their adaptation to low nutrient soils and to the fact that many species have the capacity, due to their root systems, to continue to transpire even under conditions of stress.

The research outlined derived empirical models to describe the response to a range of SO2 concentrations of agricultural species grown in a Mediterranean climate and Eucalyptus species. The next step in research should be aimed at defining exposure-response with a mechanistic basis for yield response thereby defining its qualitative and quantitative physiological basis. This would facilitate the achievement of a more complete description of plant response and provide a basis for extending the existing data to describe and predict potential plant responses to SO2 under a broader range of conditions.

Item Type: Thesis (PhD)
Murdoch Affiliation: School of Biological and Environmental Sciences
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Murray, Frank
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