Centre for Plant Biodiversity Research
Australian National Herbarium

Botanical Research, Conservation, Management
and Use of the Australian Flora

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16 September 2002

Looking underground for revegetation solutions

CSIRO Plant Industry is helping to 're-green' Australia by using soil bacteria to establish healthier native trees more quickly.

Dr Peter Thrall and his team have identified significant benefits associated with growing trees from seeds coated, or 'inoculated', with a peat-based substance containing specific strains of naturally occurring soil bacteria.

"When you look at a cleared agricultural landscape you can see there is often little or no natural vegetation left," Dr Thrall says.

"But what is not so obvious is that there is a huge diversity of soil organisms under the ground that may also be lost."

Many plants – including Australian natives such as Acacias – grow in 'symbiotic' or mutually beneficial relationships with a range of soil organisms.

"In preliminary glasshouse and field trials we have found that Acacias inoculated with beneficial strains of a nitrogen-fixing bacteria called Bradyrhizobium survive better and grow faster than un-inoculated Acacias," Dr Thrall says.

When the inoculated seed germinates and starts to grow, the bacteria form nodules on the plant's roots. These nodules take nitrogen from the air, which plants cannot use, and 'fix' it in the soil in a form they can use.

"It is this extra nitrogen, 'fixed' in the soil by the Acacias, that helps them grow better by effectively fertilising them," Dr Thrall says.

"Furthermore, we have found that other plants growing near to inoculated Acacias, such as eucalypts, grow much better too."

But not all strains of Bradyrhizobium promote plant growth – some may have a negative effect. Also, different strains of Bradyrhizobium will have different effects depending on the species of Acacia they are associated with.

Dr Thrall and his team have been analysing soil samples collected from native remnant vegetation patches to see what types of bacteria are present and sort the helpful strains from the harmful ones.

As a result, several 'elite' strains of bacteria have been identified that have been used to inoculate a number of Acacia species for a large-scale field trial.

With Greening Australia Victoria's help, eight sites on different farms in the Bendigo region have been directly sown with Acacia seed inoculated with Bradyrhizobium to assess its effect on tree health and performance.

Each site has also been planted with a range of local native species to assess the effect on them too.

"Sowing native plant seed direct into the soil is a cost-effective and practical way of establishing trees," says Mr David Millsom, Greening Australia Victoria.

"If survival rates and vigour of direct seeded trees can be improved by inoculating tree seed with bacteria then this would be a huge help to landholders wanting to replant large areas of their properties to native vegetation."

"It is exciting to think that our knowledge of revegetation is extending beneath the soil surface to re-establish not only trees and other above-ground plants, but beneficial soil organisms too," Mr Millsom says.

According to Dr Thrall, the results from the trials will improve our understanding of the relationships between plants and bacteria.

"They will also help us to identify the best strains of bacteria to inoculate seed with," Dr Thrall says.

"This project represents a significant step towards improving native plant revegetation and restoring biodiversity."

This project is a collaboration between CSIRO Plant Industry and Greening Australia Victoria with substantial on-ground support from the North Central Catchment Management Authority and the Department of Natural Resources and Environment, Victoria.

More information:

Dr Peter Thrall, CSIRO Plant Industry, 02 6246 5126

Media assistance:

Sophie Clayton, CSIRO Plant Industry,
02 6246 5139,
0418 626 860


Ms Sophie Clayton


Communication/Media Liaison Officer


CSIRO Plant Industry
GPO Box 1600
Canberra ACT 2601


+61 2 6246 5139


+61 2 6246 5299


0418 626 860





Updated 17 September, 2002 by Murray Fagg (anbg-info@anbg.gov.au)