Fossil study sheds light on famous spirals found in nature

Leaf arrangements in the earliest plants differ from most modern plants, overturning a long-held theory regarding the origins of a famous mathematical pattern found in nature, research shows.

The findings indicate that the arrangement of leaves into distinctive spirals, that are common in nature today, were not common in the most ancient land plants that first populated the earth's surface.

Instead, the ancient plants were found to have another type of spiral. This negates a long held theory about the evolution of plant leaf spirals, indicating that they evolved down two separate evolutionary paths.

Whether it is the vast swirl of a hurricane or the intricate spirals of the DNA double-helix, spirals are common in nature and most can be described by the famous mathematical series the Fibonacci sequence.

Named after the Italian mathematician, Leonardo Fibonacci, this sequence forms the basis of many of nature's most efficient and stunning patterns.

Spirals are common in plants, with Fibonacci spirals making up over 90% of the spirals. Sunflower heads, pinecones, pineapples and succulent houseplants all include these distinctive spirals in their flower petals, leaves or seeds.

Why Fibonacci spirals, also known as nature's secret code, are so common in plants has perplexed scientists for centuries, but their evolutionary origin has been largely overlooked.

Based on their widespread distribution it has long been assumed that Fibonacci spirals were an ancient feature that evolved in the earliest land plants and became highly conserved in plants.

However, an international team led by the University of Edinburgh has overthrown this theory with the discovery of non-Fibonacci spirals in a 407-million-year old plant fossil.

Using digital reconstruction techniques the researchers produced the first 3D models of leafy shoots in the fossil clubmoss Asteroxylon mackiei -- a member of the earliest group of leafy plants.

The exceptionally preserved fossil was found in the famous fossil site the Rhynie chert, a Scottish sedimentary deposit near the Aberdeenshire village of Rhynie.

The site contains evidence of some of the planet's earliest ecosystems -- when land plants first evolved and gradually started to cover the earth's rocky surface making it habitable.

The findings revealed that leaves and reproductive structures in Asteroxylon mackiei, were most commonly arranged in non-Fibonacci spirals that are rare in plants today.

This transforms scientists understanding of Fibonacci spirals in land plants. It indicates that non-Fibonacci spirals were common in ancient clubmosses and that the evolution of leaf spirals diverged into two separate paths.

The leaves of ancient clubmosses had an entirely distinct evolutionary history to the other major groups of plants today such as ferns, conifers and flowering plants.

The team created the 3D model of Asteroxylon mackiei, which has been extinct for over 400 million years, by working with digital artist Matt Humpage, using digital rendering and 3D printing.

The research, published in the journal Science, was funded by UK Research and Innovation (UKRI), The Royal Society and the German Research Foundation.

The study also involved researchers from, University College Cork, Ireland, University Münster, Germany and Northern Rogue Studios, UK.

Dr Sandy Hetherington, an evolutionary palaeobiologist and the project's lead at the University of Edinburgh, said:

"Our model of Asteroxylon mackiei lets us examine leaf arrangement in 3D for the first time. The technology to 3D print a 407-million-year old plant fossils and hold it in your hand is really incredible.

"Our findings give a new perspective on the evolution of Fibonacci spirals in plants."

Holly-Anne Turner, who worked on the project as an undergraduate student at the University of Edinburgh and is first author of the study, said:

"The clubmoss Asteroxylon mackiei is one of the earliest examples of a plant with leaves in the fossil record.

Read more at Science Daily

How photoelectrodes change in contact with water

Every green leaf is able to convert solar energy into chemical energy, storing it in chemical compounds. However, an important sub-process of photosynthesis can already be technically imitated -- solar hydrogen production: Sunlight generates a current in a so-called photoelectrode that can be used to split water molecules. This produces hydrogen, a versatile fuel that stores solar energy in chemical form and can release it when needed.

Photoelectrodes with many talents

At the HZB Institute for Solar Fuels, many teams are working on this vision. The focus of their research is on producing efficient photoelectrodes. These are semiconductors that remain stable in aqueous solutions and are highly active: Not only can they convert sunlight into electrical current, but they may also act as catalysts to accelerate the splitting of water. Among the best candidates for inexpensive and efficient photoelectrodes is bismuth vanadate (BiVO4).

What happens when in water?

"Basically, we know that just by immersing bismuth vanadate in the aqueous solution the chemical composition of the surface changes," says Dr. David Starr of the HZB Institute for Solar Fuels. And his colleague Dr. Marco Favaro adds: "Although there are a great many studies on BiVO4, it has not been clear until now exactly what implications this has on the surface electronic properties once they come into contact with the water molecules." In this work, they have now investigated this question.

Doped BiVO4 under water vapor

They studied single crystals of BiVO4 doped with molybdenum under water vapor with resonant ambient pressure photoemission spectroscopy at the Advanced Light Source at Lawrence Berkeley National Laboratory. A team led by Giulia Galli at the University of Chicago then performed density functional theory calculations to help interpret the data and to untangle the contributions of individual elements and electron orbitals to the electronic states.

Polarons on the surface detected

"In situ resonant photoemission has allowed us to understand how the electronic properties of our BiVO4 crystals changed upon water adsorption," Favaro says. The combination of measurements and calculations showed that due to excess charge, generated by either doping or defects on certain surfaces of the crystal, so-called polarons may form: negatively charged localized states, where water molecules can easily attach and then dissociate. The hydroxyl groups formed via water dissociation help to stabilize further polaron formation. "The excess electrons are localized as polarons at VO4 units on the surface," Starr summarizes the results.

Read more at Science Daily