Tree parents determine seedling survival

Scientists led by Rachael Gallagher from Australia’s Macquarie University set out to test how eucalypt seedlings cope with heatwaves – weather conditions that are quite common in many parts of the world, but which are also tipped to increase in frequency and severity as climate change bites.

To make their findings, the scientists set up laboratory-based colonies of seedlings from a type of eucalypt known as Flooded Gum (Eucalyptus grandis).

The species is widespread and commercially valuable. Gallagher and colleagues selected seedlings sourced from across its 2000-kilometre range, in which annual temperatures range from mild to extremely hot.

In the lab, all the specimens were subjected to a realistic simulated heatwave: a four day cycle in which daytime temperatures peaked at 42 degrees Celsius and never dropped below 24 at night.

The trees that had been grown from seeds gathered from areas in which average temperatures were high, and scorching periods common, coped with the heatwave much better than those that orginated in cooler regions.

The scientists discovered that the trees from hotter areas carried within their cells a greater number of protective proteins, which functioned rather like chaperones, transporting other proteins to optimal locations within the cell.

This allowed the plants to continue to function well, despite heat stress.

The presence of the protective proteins occurs at population level, with levels increasing in line with the temperature conditions historically experienced by adult trees.

“This is a significant new finding,” says Gallagher, “we have shown that trees have a ‘molecular memory’ for extreme heat.”

The result is of immediate practical use for ecologists, land managers and forestry planners. Trees, being slow-growing organisms, can take decades to adapt to changed climatic conditions. Establishing eucalypt colonies – and potentially colonies of many other species – using seedlings sourced from areas where the trees do not show protein adaptation is likely a recipe for expensive failure.

“By using this approach we can work out which populations might provide the best seed for restoring ecosystems and climate-proofing forestry as temperatures become more extreme,” explains Gallagher.

The research is published in the journal Functional Ecology.