Most trees depend on symbiotic associations between their roots and soil micro-organisms for successful establishment and growth. Their degree of dependency on these symbioses (mycorrhizas and nitrogen-fixing nodules) varies considerably, and in many cases the introduction of a tree species without the appropriate micro-organism may result in poor performance or even failure. The project leaders have recently demonstrated the potential to increase productivity of Casuarina and Eucalyptus plantations by inoculating seedlings in the nursery with selected symbionts. Projects 8808, 8809 and 8848 are selecting lesser-known tree species (including some from the genera Casuarina and Eucalyptus) with potential for fuelwood, agroforestry and soil conservation. This project complements those three. It seeks to select symbiotic micro-organisms for the two genera effective on different soil types and under a range of environmental conditions, develop appropriate inoculation technologies and transfer the relevant technology and selected micro-organisms to collaborating scientists in developing countries.
The research will concentrate on the nitrogen-fixing symbiosis between Casuarina and Frankia spp., with a small component on the ectomycorrhizal requirements of Casuarina and Eucalyptus.
The scientists will attempt to isolate Frankia strains from nodules of a number of Casuarina species growing in a wide range of climatic and soil conditions in northern Australiamainly in northern Queensland, but also from C. glauca trees growing in saline situations further south. After characterising all isolates, using gel electrophoresis, they will assess each one's symbiotic effectiveness and host range in the glasshouse, and field test selected strains with high potential for nitrogen fixation.
Inoculation studies will concentrate on simple and effective methods for introducing Frankia selections into nurseries. They will define critical inoculum levels for a number of carrier systems (compared with liquid inoculum) and investigate the effects of certain soil and environmental factors on inoculum survival and efficiency. In an assessment of nutritional factors limiting tree growth and nitrogen fixation in the field, glasshouse and field studies will concentrate on the interaction between phosphorus supply and nitrogen fixation, with some trials covering micronutrient needs.
Growth response to inoculation with effective Frankia strains will be demonstrated at field sites in Australia and in China.
In research on the ectomycorrhizas of Casuarina and Eucalyptus the team will collect, isolate and identify mycorrhizal fungi from appropriate target tree species in northeastern Australia, with the assistance of an American specialist in fungal taxonomy who is currently collaborating in research on Western Australian eucalypt mycorrhizas. The collected fungi will be grown in axenic culture and then screened for the host ranges and growth-promoting efficiency on different soil types. Glasshouse experiments will determine the phosphate needs of target-tree seedlings and establish the role of mycorrhizas in satisfying these.
Fungi selected in the glasshouse trials will be used in field studies with up to six tree species E. camaldulensis, E. grandis, E. pyrocarpa, C. equisetifolia, C. cunninghamiana and C. glaucaat two or three field sites. For Casuarina spp., the benefits of dual inoculation with ectomycorrhizal fungi and Frankia strains will be assessed.
Subsequently, the team expects to publish a handbook of techniques covering nursery practices related to Casuarina, isolation and culturing of Frankia and inoculum production and use, and will encourage the Chinese collaborators to prepare a similar publication in Chinese for local use.
This research has application throughout the tropics where both genera are widely grown: it should be possible to increase wood production substantially in areas reforested with Casuarina through inoculation with Frankia and improved management. Benefits will also flow on to Australia, where Casuarina and Eucalyptus are planted for land reclamation and as windbreaks and ornamentals and are arousing increasing interest for use in agroforestry systems.