|dc.description.abstract||Biotechnological development of transgenic crops and widespread international adoption has stimulated comprehensive research into their effects on the soil environment. Insects (both target and non-target), weeds, aquatic environments, and soils have all been extensively researched. Since the first commercial GM crop in 1995, the debate surrounding controversial aspects of their biology has polarised issues concerning insects, weeds, and the concentration of technology within a few multinational biotechnology corporations. The effect of transgenic crops on the biology of soils seemed to attract less attention. This thesis examines the interactions between transgenic canola plants through their root exudates and residues with the surrounding soil, its microbes, and their biology. The discovery of the commensal relationship of root exudates and their microbial partners has revolutionised the research into soil microbiology. From this knowledge of soil science, scientists now understand the critical importance of a healthy and abundant soil biome. This thesis focuses on the microbiology of soil. The effects of genotype on soil bacterial and fungal physiology of genetically modified (GM) canola are compared statistically with other cultivars which are genetically modified through conventional plant breeding rather than through genomic engineering, and with the canola cultivar from which the GM variety was developed. The research differentiates the effects of four canola genotypes on microbial DNA and enzymology in a greenhouse trial format. Specifically, the objective of the research is to focus on changes in microbial enzymatic activity of key functional enzymes in protein metabolism, and carbon (C), phosphorus (P), and sulphur (S) mineralisation. The effects on DNA concentration are also studied.
The main results of this research generally suggest the effects of cultivar genetic differences with respect to their interactions through root exudates and residues on microbial enzymatic activity are generally not significantly different. Moreover, there are no significant differences in the effect of root exudates on DNA concentrations. This generally accords with the majority of refereed publications and therefore provides confidence to the growing of transgenic canola and to transgenic plants and technology generally. The review and analysis conducted also indicates an emerging trend to broaden the research efforts onto the study of farms and the systems of agriculture under which crops are grown. The findings of this thesis are based on an experimental method and data gathering using phosphorescence to measure changes in enzyme activity and DNA concentration. The statistical analysis employed ANOVA with randomised complete blocking for repeated measures using multiple sampling during the course of the plant‘s lifespan. Further statistical analysis using one-way ANOVA and sequential linear modelling were also employed to study the nature of effects in more detail where the initial analysis suggested significant differences. Furthermore, panel regression analysis examined time-series effects to gain an understanding of how sampling date and therefore stage of the plant‘s growth affected outcomes. The panel analysis indicated that Beta-gluconase enzyme activity significantly influenced soil DNA concentrations. There were limited numbers of occasions when statistical differences between genotypes were found. Overall the experimental results favour the argument that the transgenic canola crops do not damage the soil environment in any significant manner. Therefore it seems that the crops may safely continue to play a major role in meeting the future challenges of world food security. The qualitative data gathered via visits to contributing canola growers during the study enabled comparisons to be made between real world practices with experimental results, as well as results from the literature. Together such a process allowed the author to gain significant insights into the complex decisions the farmers must make in the choice of their employed technologies, including seed genetics.
In summary, the major findings are:
minimal impact on protein and amino acid metabolism;
little or no effect on P mineralisation;
carbohydrate metabolism through breakdown of C residues unaffected;
minimal changes in S metabolism;
insignificant differences in DNA concentrations between genotypes;
some insights gained into the nutrient needs of microorganisms;
measurement by phosphorescence is both practical and inexpensive;
there were a number of environmental advantages emerging from the use of GM technology, including improved accumulations of soil carbon through organic matter increase and improvement in soil structure and fertility, as well as changes to less toxic and persistent herbicides;
productivity improvement created by GM technology is comparable with results from conventional plant breeding
There are some limitations to the study that should be noted, as follows:
The impact of herbicides on microbial physiology was not explored due to aspects beyond the scope of this study;
The study on the whole was a greenhouse situation and did not directly involve farms;
The study was limited to one soil type (Vertisol) as a second soil type (Chromosol) inhibited germination and growth of the canola seedlings. An attempt to explore the types and Orders of microbes and how they changed during the development of the various plant genotypes was unsuccessful technically.
The following areas are suggested as being relevant for further investigation:
Phospho Lipid Fatty Acid extractions and genomic techniques remain desirable technologies if resources and experience are available to implement them. These complex technologies can quantify individual microorganisms, including pathogens, giving deeper understanding;
Additional information about the effect of herbicides on the criteria being measured would be helpful in differentiating their impact alone on microbial function. This would require special analytical chemistry procedures for herbicide residue extraction and chromatography, a larger study, and greater financial resources;
Translating the experiment to a field study over several years in differing soil types would produce additional information such as yields, production penalties, respective costs, and practical outcomes, as well as soil microbial effects and thus provide a complete picture for the issues involved. Hence a clearer choice of the systems under which different cultivars are grown can be related to environmental outcomes.||