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.

Item provided courtesy of CSIRO