Midwood: We have discovered an entirely new kind of wood

Scientists have discovered an entirely new kind of wood, a finding that could turbocharge trees’ ability to store carbon.

Tulip trees feature a nanoscale wood structure that sits somewhere between hardwood and softwood, dubbed “midwood”, which may explain why they are so effective at storing carbon.

Jan Łyczakowski at Jagiellonian University in Poland and his colleagues investigated the nanoscale structure of live wood samples taken from 33 species of trees in the botanic garden at the University of Cambridge in the UK.

They froze each sample in a “slush nitrogen” that held specimens at a temperature of –210°C, before studying each one under a low-temperature scanning electron microscope.  This allowed them to anlayse the size of each wood type’s macrofibrils, tiny rod-like filaments that house wood cells.

They found that hardwood trees, such as oak or birch, have macrofibrils about 15 nanometres in diameter, whereas softwood trees, such as pine or spruce, have larger macrofibrils of 25 nanometres or more in diameter.

But there was one “surprise” exception, says Łyczakowski. The two surviving species of the Liriodendron genus, the tulip tree (Liriodendron tulipifera) and the Chinese tulip tree (Liriodendron chinense), had macrofibrils of around 20 nanometres, midway between softwood and hardwood. “Liriodendron, for some unknown reason, has a different macrofibrial structure,” he says.

“We knew then there was something special about the liriodendrum,” says Raymond Wightman at the University of Cambridge. 

Previous research has demonstrated that Liriodendrons are fast-growing with high carbon sequestration rates, making them popular candidates for carbon plantation schemes.

Liriodendrons diverged from their close relative Magnolia (Magnoliids) around 30-50 million years ago, a point in Earth’s history when atmospheric CO2 concentrations dropped sharply from 1000 parts per million (ppm) to around 320ppm.

The trees may have developed larger macrofibrils to make them more effective at drawing carbon from the atmosphere as concentrations fell, Łyczakowski suggests. Łyczakowski now wants to test that theory, by bioengineering trees to have midwood-sized macrofibrils and then testing their carbon sequestration rate. If it turns out midwood-sized macrofibrils are best suited for carbon sequestration, it may be possible to breed other tree species with those optimum-sized macrofibrils to boost their carbon storing capacity, he says.