Tulip Tree Wood Could Transform Carbon Storage

A garden tree valued for its attractive blooms and leaves has been concealing an unexpected property.

The wood produced by the two tulip tree species (Liriodendron) is not classified as either hardwood or softwood. Instead, it represents an intermediate form of wood, a category that had not previously been recognised. Researchers say this material also appears to be especially effective at sequestering and retaining carbon.

Tulip tree wood and carbon storage

According to biochemists Jan Łyczakowski of Jagiellonian University in Poland and Raymond Wightman of Cambridge University in the UK, this capacity may stem from the size of the trees’ macrofibrils. These long, thread-like bundles of cellulose and cell-wall components are considerably larger than macrofibrils found in hardwood trees.

The finding could also open up new approaches to carbon storage.

"Both tulip tree species are known to be exceptionally efficient at locking in carbon, and their enlarged macrofibril structure could be an adaptation to help them more readily capture and store larger quantities of carbon when the availability of atmospheric carbon was being reduced," Łyczakowski explains.

"Tulip trees may end up being useful for carbon capture plantations. Some east Asian countries are already using Liriodendron plantations to efficiently lock in carbon, and we now think this might be related to its novel wood structure."

There are two tulip tree species, Liriodendron tulipifera and Liriodendron chinense. Their evolutionary lines date back 30 to 50 million years, when they separated from the Magnolia genus.

At roughly that period, atmospheric carbon dioxide levels fell rapidly and dramatically. The researchers suggest that this decline may be connected to the emergence of Liriodendron.

"This," Łyczakowski explains, "might help explain why tulip trees are highly effective at carbon storage."

Macrofibrils in woody plant cell walls

Macrofibrils occur in the secondary cell walls of woody plants, a central part of their anatomy. Formed after the primary cell walls, these secondary walls strengthen the plant’s overall structure.

Most of a plant’s woody biomass is located here, yet relatively little is known about it.

Łyczakowski and his colleagues identified the unusual wood while investigating how the structures of these plants evolved. Their work covered softwood plants, including pines and conifers, as well as hardwoods such as oak and birch.

Using scanning electron cryomicroscopy (cryo-SEM), the team examined the cell walls of 33 plants in a state as close to natural as possible. The process involved collecting the wood, preserving it and imaging it for hours, allowing the researchers to observe it as it exists in life rather than in the dry, desiccated condition typical of dead wood.

Evolutionary insights from tulip trees

The research showed that distinctions between angiosperms, or flowering plants, and gymnosperms, or seed-producing plants, are not invariably straightforward.

Alongside the identification of a new wood type, the researchers found that two gymnosperms from the Gnetum genus possess secondary cell walls structured in the same way as those of woody angiosperms.

The pair describe this as an instance of convergent evolution, in which separate species independently acquire the same characteristics. Taken together, the results offer fresh insight into the evolutionary links between plant cell-wall composition and the nanostructure of wood.

These discoveries matter across disciplines, from biology to engineering.

"The main building blocks of wood are the secondary cell walls, and it is the architecture of these cell walls that give wood its density and strength that we rely on for construction," Łyczakowski says.

"Secondary cell walls are also the largest repository of carbon in the biosphere, which makes it even more important to understand their diversity to further our carbon capture programmes to help mitigate climate change."

The research was published in New Phytologist.