Ectomycorrhizal fungi for eucalypt plantations in China

• Xinhui Forest Bureau, China
• Chinese Academy of Forestry, China
• Gaoyao Forest Bureau, China
• Chuxiong District Forest Research Institute, China
• Kunming Institute of Botany, China
• Murdoch University, Australia

Australian eucalypts have become important in China and parts of Southeast Asia for rehabilitating sites previously under native forest. The eucalypts are more productive than indigenous trees, and their growth can be enhanced in the early establishment phase if compatible Australian ectomycorrhizae are present.
Ectomycorrhizae are soil fungi that ensheath roots and form a symbiotic association with a host plant, in this case a eucalypt. The fungus makes soil nutrients more available to a compatible host, partly by enlarging the roots' absorptive surface area.
Plantation managers need to balance the yield of the trees against the cost of artificial fertilisers. However, if appropriate mycorrhizal fungi are present, plant responses to applied fertilisers should be optimised. In fact, the mycorrhizal partnership with the tree is most useful in soils where lack of nutrients - especially phosphate, but also potassium, nitrogen and trace elements including boron - limits tree growth.

This project aimed to match the ectomycorrhizal fungi to important plantation eucalypts in China in a range of climatic and soil situations.

Individual species and isolates of ectomycorrhizae vary in their abilities to extract nutrients from the soil matrix and otherwise modify soil conditions for the host. In Australia, only about 5% of Australian ectomycorrhizal fungi had been characterised. Cultures of ectomycorrhizae were maintained by repeated subculture, and inoculated into the eucalypt nursery soils - as crushed spores, sporophores, or mycelia. (Each form of inoculum has advantages and disadvantages, and not every form is available for every fungus.)
A series of small trials was set up in China on phosphate-deficient sites. Eucalypts commercially important to China, such as Eucalyptus grandis, E. globulus and E. urophylla x E. grandis, were planted, inoculated with Australian mycorrhizal fungi from the CSIRO collection, then fertilised at various rates. The trials measured the interactions between rate of fertiliser application and inoculation with ectomycorrhizal fungi, with the intention of demonstrating the extra benefit possible from using Australian ectomycorrhizae.
The demonstration would only be valid if it could show that the fungi colonising the eucalypt roots were actually those that had been inoculated. A bioassay was developed to identify the colonising fungi. The project also produced an atlas by which field officers could identify the ectomycorrhizae. Some fungi could be recognised from their fruiting bodies - toadstools, puffballs, truffles and so on - but the atlas also depicted the morphology of mycorrhizal roots, for identification when a fungus is not fruiting. Preliminary work continued on identifying fungi by DNA fingerprinting.
A series of tests was designed for plantation soils to identify their nutrient status and also the resident indigenous fungi.

Before plantation managers could start using eucalyptus root stock inoculated with ectomycorrhizal fungi, the project team had to develop cost-effective spore inoculation procedures for ectomycorrhizal fungi and identify site factors determining mycorrhizal responses and nutrient interactions in eucalypt plantations. Field trials were established at three sites in China (two in Guangdong Province and one in Yunnan) to test Australian mycorrhizal fungi in phosphorus-deficient soils. Molecular techniques were developed for confirming the presence of some introduced fungi on tree roots in the field.
Recommendations for macro- and micronutrient fertilisers for eucalypt plantations in China were also developed. Knowledge and skills were transferred through practical training and extension activities including mycorrhizal workshops in China. Chinese-language handouts and ACIAR research notes with recommended procedures for managing mycorrhizal plants in the nursery and in the field were produced and distributed.
During the project extension, scientists from CSIRO developed a website containing information on mycorrhizal fungi (see http://www.ffp.csiro.au/research/mycorrhiza/intro.html). As well, the ACIAR monographs Nutrient disorders in plantation eucalypts (first edition by B Dell, N Malajczuk & TS Grove issued as monograph 31 in 1995; revised edition by B Dell, N Malajczuk, D Xu & TS Grove issued as monograph 74 in 2001) are widely used by the industry.
This project resulted in about 25 per cent of total plantings now being inoculated in nurseries, and this should rapidly lead to the majority of private forest companies inoculating over 50 per cent of their clonal eucalypts. Inoculation with ectomycorrhizal fungi increases the sustainability of plantations by improved nutrient cycling and greater efficiency in the use of fertiliser by trees. In addition, it is estimated that tree productivity will be increased by a further 10 cubic metres/hectare/year MAI (mean annual increment) as a result of the improved fertiliser regime suggested by the project.
All new commercial eucalypt plantations are being supplied with fertiliser manufactured in China containing appropriate macronutrients (nitrogen, phosphorus, potassium and sulfur) and appropriate micronutrients such as boron and/or zinc. At least three companies are producing their own blend of compound fertiliser.
Several companies are routinely using foliar analysis to determine limiting nutrients for tree growth. Scientists in China are now able to provide start-up inoculum to forestry companies and the Forestry Bureaus. They have also extended the applied research from eucalypts to agricultural crops such as banana, litchi, longan, cassava and to ornamental crops such as flowering plants. Forest technicians are providing advice on mycorrhizal technology in the regions to nursery managers.