Australian experts have contributed to an exciting new finding – working out how trees pull water up to their very highest branches.

It solves a long-standing scientific mystery, according to QUT physicist Dr Stephen Hughes.

Researchers from QUT and the University of Leicester, led by chemist Dr Adrian Boatwright, examined the phenomenon.

How water gets pulled to the top of tree branches has been a perplexing question, because traditional thinking says the barometric limit would stop it getting any higher than 10.06m.

“How is it that trees can pull water up to the top most branches? This question has troubled both botanists and physicists for many years with various mechanisms used to describe this process - ranging from capillary action to osmotic pressure," said Dr Boatwright, from the University of Leicester's Department of Chemistry.

The researchers discovered that water can be held in a vacuum for almost indefinite periods of time and even under significant tension without forming bubbles or breaking apart, which helps to explain how trees siphon water to their highest points.

“By siphoning water up to as much as 13.7m we have managed to ‘break’ the barometric limit and show that the maximum height is limited only by the strength of bonds in the water,” Dr Boatwright said.

While the widespread view has been that siphons work because of atmospheric pressure, recent research has shown that cohesion and gravity, and not atmospheric pressure is the driving principle.

“The first recorded use of siphons was in ancient Egypt circa 1430 BC," said Dr Hughes, from QUT's Science and Engineering Faculty.

“Our experiment, conducted over 3,400 years later, is the first report published in the scientific literature of a siphon operating over the barometric limit.

“How siphons work has been quite controversial. This experiment is a clear demonstration that siphons work through gravity and not atmospheric pressure as is commonly supposed.”

More details are available in the full report, here.