Summary of final report on the Australian Flora Foundation funded project:
Dr G. C. Kirby,
The grant was expended on several small experiments and one larger experiment. The small experiments were pilot studies whilst I tried to develop the procedures and techniques needed to conduct experiments with Sturt Peas, Rhizobia bacteria and mycorrhizal fungi. The larger experiment was a study of the effects of different native soils and heat sterilisation treatments on the levels of microbial infection and growth of Sturt Pea seedlings.
The results can be summarised as follows :
1) Good growth and nodulation of some seedlings occurred, so the nutrient solution (1/10th strength hydroponic solution) was not so weak that growth was impeded too much nor was it so rich in nitrogen that nodulation was discouraged.
2) There were no statistically significant effects of heat sterilisation on the number of nodules (P ~ 0.15) or the wet weight of seedling tops (P ~ 0.9), nor did the appearance of mycorrhizal fungi differ between the treatments within soils (visual appraisal only). These microbes appear to be fairly resistant to dry heat – perhaps as an adaptation to long term survival in arid zone soils where high temperatures can occur in surface regions on summer days. A follow up experiment with two soils autoclaved for 30 min at 120?°C again failed to show any differences from the controls in seedling growth and nodulation (visual examination only).
3) there were highly significant differences between soils in the number of nodules (P << 0.001) and the top weight of seedlings (P ~ 0.002)
4) there does appear to be a correlation between seedling size and the presence of VAM but not external hyphae (which may well be saprophytic fungi rather than mycorrhizal fungi). However, the possible correlation between VAM and seedling size cannot be used to infer causation in this experiment.