Unlocking the secrets of the green-and-gold

Published 13 June 2017

Wattles – they are one of Australia’s largest and best loved plant groups, widely celebrated in literature and song, and even recognised with their own official day, but much about them has remained a mystery. Until now.

UNE’s Dr Nigel Warwick has enlisted the help of one of the world’s oldest botanic gardens to unlock some of the secrets of the fascinating genus Acacia. He has just made his third trip to the Royal Botanic Gardens in Kew, London, where he carried out some of the world’s first comprehensive studies of wattle anatomy.

“Acacias are some of the most hardy and resilient plants in the world,” said Dr Warwick. “They possess a number of adaptations that allow them to transport water and nutrients and to survive tough drought conditions. Learning how they cope with drought and heat stress may provide some clues as to how they and other plants will tolerate the hotter, drier conditions projected under climate change.”

Acacia xylem under the microscope.

Wattles, of which there are some 1200 species in Australia, are a dominant feature across a range of landscapes. Dr Warwick, a plant physiologist (who studies how plants adapt to different environmental conditions, including drought, salinity and temperature), is comparing more than 50 species that grow in a climate gradient across northern New South Wales – from the red-stemmed wattle that lives on the north coast, enjoying an average annual rainfall of 1400 millimetres, to the mulga that ekes out a meagre existence in the semi-arid zone near Broken Hill, where as little as 200 millimetres fall each year.

“I am trying to understand how the anatomy and physiology of the plants has evolved to cope with drought and heat, and I do this by looking at the structures at a cellular and sub-cellular level,” Dr Warwick said. “I have found that the Acacias living in drier environments have different plumbing. They have more xylem vessels that conduct water and nutrients through the plant, and these vessels are slightly narrower, and they are fitted with special seals that prevent their plumbing from collapsing during dry periods.”

Using light and scanning electron microscopy, Dr Warwick has been able to study both the anatomy of Acacia wood and foliage. His findings improve our understanding of entire forest and woodland ecosystems, many of which rely on Acacias.

“Bacteria living in the roots of Acacias fix nitrogen from the atmosphere in the soil, which contributes to soil fertility, making Acacias very important to surrounding plants and the nitrogen cycle within an ecosystem,” Dr Warwick said.

Acacias are also economically important. A number of Australian species are planted around the world as a source of timber, firewood, pulp and paper, tannins, dyes, gums for food products and pharmaceuticals, and stock fodder. Timber, pulp and paper production, especially, depends on the characteristic anatomy of the wood.

Since 2010, Dr Warwick has forged a strong and productive research link with Dr Peter Gasson, a leading wood anatomist and researcher in the Jodrell Laboratory at the Royal Botanic Gardens in Kew. Microscope slides of Acacias that Dr Warwick prepared now form part of the Gardens’ permanent collection and will soon be available online to scientists globally.

And that’s not his only gift to science. Along the way Dr Warwick has produced an unexpected artistic by-product. Beautiful samples that he sectioned and stained for microscopic analysis have been photographed and now feature on complimentary bookmarks and postcards in the Kew Gardens gift shop.