Researchers conducting an evolutionary study of the microscopic structure of wood from some of the world’s most iconic trees and shrubs have discovered an entirely new type of wood.
This discovery could open up new opportunities to improve carbon sequestration in plantation forests by planting a fast-growing tree more commonly seen in ornamental gardens.
The research showed that tulip trees, which are related to magnolias and can grow to more than 30 meters tall, have a unique type of wood that does not fit into any of the hardwood or softwood categories.
Scientists from the Jagiellonian University and the University of Cambridge used a low-temperature scanning electron microscope (cryo-SEM) to image the nanoscale architecture of secondary cell walls (wood) in their native hydrated state.
The researchers found the two surviving species from ancient times Liriodendron genus, commonly known as the Tulip Tree (Liriodendrontulpifera) and Chinese Tulip Tree (Liriodendron chinense) have much larger macrofibrils than their hardwood relatives (macrofibrils are long fibers aligned in layers in the secondary cell wall).
Lead author of the study published in New phytologistDr. Jan Łyczakowski from Jagiellonian University said: “We show it Liriodendrons have an intermediate macrofibril structure that differs significantly from the structure of softwood or hardwood. Liriodendrons diverged from magnolia trees about 30-50 million years ago, coinciding with a rapid reduction in atmospheric CO22. This could help explain why tulip trees are very effective at storing carbon.”
The team suspects that it is the larger macrofibrils in this ‘middle wood’ or ‘accumulator wood’ that are responsible for the rapid growth of the tulip trees.
Łyczakowski added: “Both types of tulip trees are known to be exceptionally efficient at capturing carbon, and their enlarged macrofibril structure could be an adaptation to help them more easily capture and store larger amounts of carbon when carbon availability in the atmosphere was reduced. Tulip trees can be useful for carbon capture plantations. Some East Asian countries are already using them Liriodendron plantations to capture carbon efficiently, and we now think this may be related to the new wood structure.”
Liriodendrontulpifera are native to North America and Liriodendron chinenseis a native species of central and southern China and Vietnam.
The discovery was part of a study of 33 tree species from the Living Collections of the Cambridge University Botanic Garden, which examined how the ultrastructure of wood evolved in softwoods (gymnosperms such as pine and conifers) and hardwoods (angiosperms including oak, ash, birch and eucalyptus trees).
Łyczakowski said: “Despite its importance, we know little about how the structure of wood evolves and adapts to the external environment. We have made some important new discoveries in this research – a completely new form of ultrastructure of wood that has never been seen before observed and a family of gymnosperms with angiosperm-like hardwoods instead of the typical gymnosperm softwoods.
“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 store of carbon in the biosphere, making it even more makes it more important to understand their diversity to advance our carbon capture programs and help mitigate climate change.”
Ultrastructure of wood
Ultrastructure of wood refers to the detailed microscopic architecture of wood, which includes the arrangement and organization of its material components. This research on wood using a cryo-scanning electron microscope focused on:
- The secondary cell wall: This consists mainly of cellulose plus other complex sugars and is impregnated with lignin to make the entire structure stiff. These components form the macrofibrils, forming long aligned fibers arranged in different layers within the secondary cell wall.
- The macrofibril: This is currently the smallest structure we can measure using cryoSEM and is on the order of 10 to 40 nanometers thick. It is composed of cellulose microfibrils (3-4 nanometers) plus other components.
Studying the ultrastructure of wood is crucial for several applications, including wood processing, materials science and understanding the ecological and evolutionary aspects of trees. Understanding the biology behind tree growth and wood deposition is also valuable information when calculating carbon capture.
The Living Collections of Cambridge University Botanic Garden
The wood samples were collected from trees in the Cambridge University Botanic Garden in collaboration with Margeaux Apple, the garden’s collections coordinator. Fresh wood samples deposited in the previous spring growing season were collected from a selection of trees to represent the evolutionary history of gymnosperm and angiosperm populations as they diverged and evolved.
Microscopy Core Facility Manager at the Sainsbury Laboratory Cambridge University, Dr Raymond Wightman, said: “We analyzed some of the world’s most iconic trees, such as the giant sequoia, Wollemi pine and so-called “living fossils” such as Amborella trichopodathe only surviving species of a plant family that was the earliest extant group to evolve separately from all other flowering plants.
“Our research data has given us new insights into the evolutionary relationships between wood nanostructure and cell wall composition, which differs between the sexes of angiosperm and gymnosperm plants. Angiosperm cell walls possess characteristically narrower elementary units, called macrofibrils, compared to gymnosperms and this small macrofibril formed after divergence of the Amborella trichopoda Ancestor.”
Lyczakowski and Wightman also analyzed the cell wall macrofibrils of two gymnosperm plants from the Gnetophytes family –Gnetum gnemon AndGnetum edule— and confirmed that 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 developed a hardwood-like structure normally found only in angiosperms.
The research was carried out while Britain was sweltering under the British 4e warmest summer ever measured in 2022.
“We think this could be the largest study, using a cryo-electron microscope, of woody plants ever done,” Wightman said. “It was only possible to conduct such a large study on freshly hydrated wood because the Sainsbury Lab is located in the grounds of the Cambridge University Botanic Garden. We collected all the samples in the summer of 2022 – collected in the early morning, at freezing point, the samples in ultracold slush nitrogen and then the samples are imaged until midnight.
“This research illustrates the continued value and impact that botanical gardens have in contributing to contemporary research. This study would not be possible without such a diverse selection of plants represented through evolutionary time, all growing together in the same place at the University from Cambridge Collections Botanical Garden.”
