Researchers from the University of Cambridge and Jagiellonian University, Poland, have discovered an entirely new type of wood that does not fit into either category of hardwood or softwood. This discovery may open new opportunities to mitigate climate change by improving carbon capture and storage in carbon capture plantation forests, by planting a fast-growing tree more commonly seen in ornamental gardens.
The study found that tulip trees, which are related to magnolias and can grow over 100 feet tall, have this unique type of wood.
The discovery was part of an evolutionary survey of the microscopic structure of wood from 33 tree species from CUBG’s Living Collections. The survey explored how the arrangement and properties of the cell walls of wood (wood ultrastructure) evolved across softwoods (gymnosperms such as pines and conifers) and hardwoods (angiosperms or flowering plants including oak, ash, birch, and eucalypts).
We’ve made some key new discoveries in this survey – an entirely novel form of wood ultrastructure never observed before and a family of gymnosperms with angiosperm-like hardwood instead of the typical gymnosperm softwood.
Lead author of the research published in New Phytologist, Dr Jan Łyczakowski from Jagiellonian University, explains: “Despite its importance, we know little about how the structure of wood evolves and adapts to the external environment. We’ve made some key new discoveries in this survey – an entirely novel form of wood ultrastructure never observed before and a family of gymnosperms with angiosperm-like hardwood instead of the typical gymnosperm softwood.
“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. 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 wood samples were collected from trees in the Botanic Garden in coordination with CUBG’s Collections Coordinator. Fresh samples of wood, deposited in the previous spring growing season, were collected from a selection of trees to reflect the evolutionary history of gymnosperm and angiosperm populations as they diverged and evolved.
Scientists used a low temperature scanning electron microscope (cryo-SEM) to image the nanoscale architecture of secondary cell walls (wood) in their native hydrated state. This allows scientists to see the cells while they are still in their living state, rather than using dried or chemically treated samples.
The research illustrates the continued value and impact that botanic gardens have in contributing to modern day research. This study would not be possible without having such a diverse selection of plants represented through evolutionary time, all growing together in the same place in the Botanic Garden’s Collections.
They found that the two surviving species of the ancient Liriodendron genus, commonly known as the tulip tree (Liriodendron tulipifera) and Chinese tulip tree (Liriodendron chinense), have much larger macrofibrils (long fibres aligned in layers in the secondary cell wall) than their hardwood relatives.
The team suspect it is the larger macrofibrils in this ‘midwood’ that is behind the tulip trees’ rapid growth.
Dr Jan Łyczakowski continues: “We show Liriodendrons have an intermediate macrofibril structure that is significantly different from the structure of either softwood or hardwood. Liriodendrons diverged from magnolia trees around 30-50 million years ago, which coincided with a rapid reduction in atmospheric CO2. This might help explain why tulip trees are highly effective at carbon storage.”
Liriodendron tulipifera are native to northern America and Liriodendron chinense is a native species of central and southern China and Vietnam. Dr Łyczakowski says: “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. 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.”
Microscopy Core Facility Manager at the Sainsbury Laboratory Cambridge University, Dr Raymond Wightman, explains more about the study: “We analysed some of the world’s most iconic trees like the coastal redwood, Wollemi pine and so-called ‘living fossils’ such as Amborella trichopoda, which is the sole surviving species of a family of plants that was the earliest still existing group to evolve separately from all other flowering plants.
“Our survey data has given us new insights into the evolutionary relationships between wood nanostructure and the cell wall composition, which differs across the lineages of angiosperm and gymnosperm plants. Angiosperm cell walls possess characteristic narrower elementary units, called macrofibrils, compared to gymnosperms and this small macrofibril emerged after divergence from the Amborella trichopoda ancestor.”
Lyczakowski and Wightman also analysed the cell wall macrofibrils of two gymnosperm plants in the Gnetophytes family – Gnetum gnemon and Gnetum edule (growing in CUBG’s Glasshouse Range) – and confirmed both have a secondary cell wall ultrastructure synonymous with the hardwood cell wall structures of angiosperms. This is an example of convergent evolution where the Gnetophytes have independently evolved a hardwood-type structure normally only seen in angiosperms.
The survey was undertaken while the UK was sweltering under the UK’s fourth hottest ever recorded summer in 2022.
“We think this could be the largest survey, using a cryo-electron microscope, of woody plants ever done,” Dr Wightman says. “It was only possible to do such a large survey of fresh hydrated wood because the Sainsbury Lab is located within the grounds of the Botanic Garden. We collected all the samples in the early morning, freezing the samples in ultra-cold slush nitrogen and then imaging the samples through to midnight.
“The research illustrates the continued value and impact that botanic gardens have in contributing to modern day research. This study would not be possible without having such a diverse selection of plants represented through evolutionary time, all growing together in the same place in the Botanic Garden’s Collections.”
Reference: Jan J Lyczakowski and Raymond Wightman (2024) Convergent and adaptive evolution drove change of secondary cell wall ultrastructure in extant lineages of seed plants. New Phytologist. DOI: https://doi.org/10.1111/nph.19983
This research was supported by grants from National Science Centre Poland and The Gatsby Charitable Foundation.
This article was originally written by Sainsbury Laboratory, Cambridge University.
