Survival in salty alkaline soils

Australian wattles are tough, especially when it comes to growing and thriving in salty and alkaline soils.

In an attempt to shed more light on the evolution of this salt and alkalinity tolerance, Dr Elisabeth Bui and colleagues from CSIRO found that acacias have repeatedly and often together evolved salinity and alkalinity tolerance.

Australia’s soils are old and contain large, sometimes overlapping, areas of high salt and alkalinity.

Saline or alkaline soils place a lot of stress on plants. When a plant faces these conditions together this can be even more deleterious than dealing with them alone.

Most plants can only tolerate low concentrations of salt before they die and most cultivated plants prefer acidic (pH 5.5-6.5) rather than alkaline soils. However, many Australian plants, especially the acacias and saltbushes, can tolerate salt and alkaline conditions.

Acacias have radiated into more than 1000 species across Australia over 25 million years and have evolved the ability to thrive in this stressful soil environment.

Bui and colleagues investigated this tolerance by predicting the average soil salinity and pH for 503 acacia species. They then mapped the results onto a maximum-likelihood phylogeny chart to visualise lines of descent and relationships among the different species.

The results showed that geographically restricted species were often tolerant of extreme conditions - highly saline and alkaline soils. There was also strong evidence that many acacia have distributions affected by salinity and alkalinity and that preference is lineage specific.

By understanding the genetic relationship between salt and alkaline tolerance in acacia, new insights into plant breeding for stress tolerance may improve the ability to rehabilitate land at risk from dryland salinity as well as agriculture in these extreme environments.

This study was published in Biology Letters.