News

A global team of researchers, our Professor Ülo Niinemets included, have cracked the mystery of leaf size. Their research was published on Friday as a cover story in Science.

Why are leaves generally much larger in tropical jungles than in temperate forests and deserts?

The research, led by Associate Professor Ian Wright from Macquarie University, reveals that in much of the world the key limiting factor for leaf size is night temperature and the risk of frost damage to leaves.

Ian, and 16 colleagues from Australia, the UK, Canada, Argentina, the USA, Estonia, Spain, and China analysed leaves from over 7,600 species, then teamed the data with new theory to create a series of equations that can predict the maximum viable leaf size anywhere in the world based on the risk of daytime overheating and night-time freezing.

The researchers will use these findings to create more accurate vegetation models. This will be used by governments to predict how vegetation will change locally and globally under climate change, and to plan for adaptation.

For scientists it’s been a century-old conundrum: why does leaf size vary with latitude – from very small near the poles to massive leaves in the tropics?

“The conventional explanation was that water availability and overheating were the two major limits to leaf size. But the data didn’t fit,” says Ian. “For example the tropics are both wet and hot, and leaves in cooler parts of the world are unlikely to overheat.”

“The most surprising result was that over much of the world the maximum size of leaves is set not by the risk of overheating, but rather by the risk of damaging frost at night. Larger leaves have thicker, insulating “boundary layers” of still air that slows their ability to draw heat from their surroundings – heat that is needed to compensate for longwave energy lost to the night-time sky,” says co-author Colin Prentice from Imperial College London, who co-ordinated the mathematical modelling effort.

Ülle Jaakma, Prorector of Science of Estonian University of Life Sciences, said that to get your article published on the front page of Science is a really big acknowledgment for every scientist.

Professor Ülo Niinemtes is one of the most cited scientists in the world.