How a thin coated film could upgrade photosynthesis and feed 9 billion people

A thin film coated with the rare-earth metal europium is boosting plant productivity. How might this assist in supplying the planet with food in the future?
Sade Agard
Plant-boosting thin film could help feed our planet in colder climates
Plant-boosting thin film could help feed our planet in colder climates

Vladimir Zapletin/ iStock 

  • Scientists have created a plant-boosting coating that converts high-energy UV light from the sun into lower-energy red light, which plants can use in photosynthesis.
  • The technology requires no electricity and demonstrated accelerated growth in both green leafy vegetables and trees.
  • It is hoped that the technology may one day be utilized to enhance food production in colder climates while tackling several other sustainable development goals (SDGs).

The emergence of life on Earth depended heavily on the evolution of photosynthesis- the process by which plants and some other organisms use sunlight, water, and carbon dioxide to generate oxygen and energy in the form of sugar.

Still, as ancient as photosynthesis is - around 3.5 billion years old, to be a bit more precise - it's surprisingly inefficient. Only a tiny portion of the sunlight reaching a plant is used to fuel its growth, which means our crops produce less food than theoretically possible.

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Given our growing food requirements- which is needed to feed a burgeoning global population, predicted to total around nine billion by the year 2050- some researchers have asked themselves whether we could make plants that absorb sunlight more effectively to meet the challenge.

Researchers from Hokkaido University and the Institute for Chemical Reaction Design and Discovery (WPI-ICReDD) have proposed just that. They have developed a thin film coated with the rare-earth metal europium (Eu3+). They claim their cutting-edge technology can increase plant productivity and address problems with the world's food supply, particularly in colder locations. Better yet, it requires zero electricity.

Interesting Engineering (IE) spoke with the lead scientist Dr. Sunao Shoji, to learn more.

Photosynthesis is most efficient with red and blue light

As much as sunlight is a sustainable energy source, only a fraction of its full spectrum is actually used for photosynthesis. This is because chlorophyll, the green pigment responsible for the color of leaves, is most effective at absorbing light in the red and blue regions of the visible light spectrum, which together account for less than half of all the light that reaches Earth.

Additionally, plants cannot fully utilize all of the energy they absorb from the sunlight to generate biomass. This relates to the presence of ultraviolet (UV) rays, especially UV-B. Excessive exposure to this can cause plants harm, as is the case with humans and other animals. As a protective mechanism, rather than using UV light, the plant finds a way to get rid of it in a process known as non-photochemical quenching, or photo-protection.

In this process, excess absorbed light energy is dissipated into heat. This prevents protons from forming more quickly than the plant can use them, preventing excess energy from being absorbed and damaging critical components of the plant’s molecular machinery. However, natural inefficiencies in the way that plants react to changes in the amount of sunlight they receive mean that plants reject a lot of energy that they could be using to build more biomass.

This is where the europium-based (Eu3+) thin-film coating comes in.

'This material is able to convert higher energy ultraviolet light... into red light'

How a thin coated film could upgrade photosynthesis and feed 9 billion people
The wavelength converting film can be applied to commercially available plastic sheets.

"For this project, we developed a thin film coating containing a luminescent europium complex that is able to change the wavelength of incoming light," explained Dr. Sunao Shoji.

"This material is able to convert higher energy ultraviolet light from the sun into lower energy red light, which plants can use in photosynthesis."

Essentially, in the study, researchers developed a wavelength-converting material (WCM) based on a Eu3+ complex and made a thin-film coating that can be applied to commercially available plastic sheets.

When positioned over plants growing in direct sunshine, the researchers demonstrated that the film converts UV light to red light. Additionally, it doesn't block any beneficial visible light from the sun. In this way, plants received additional visible light that they can use in photosynthesis, resulting in accelerated growth.

The film was then put to the test by comparing plant growth using sheets with and without the WCM coating. The latter being the 'control.'

Accelerating growth in leafy vegetables and trees

How a thin coated film could upgrade photosynthesis and feed 9 billion people
Accelerated growth in a larch tree: left shows without film (control)

"We were pleasantly surprised that we saw accelerated growth for both Swiss chard, a vegetal crop, and Japanese larch, a tree plant," revealed Shoji.

While no significant difference was observed for Swiss chard in summer when using the WCM films - winter was a different story. The researchers found that when days are shorter and the sunlight weaker, Swiss chard plants grown using the WCM films showed 1.2 times greater plant height and 1.4 times greater biomass after 63 days.

Trials with Japanese larch trees also demonstrated accelerated growth. In the first four months of development, seedlings exhibited a greater relative growth rate, resulting in a 1.2-fold larger stem diameter. According to the researchers, the overall biomass was also 1.4 times greater than that of trees growing without the WCM covering.

Crucially, this made it possible for the seedlings to grow to the standard size for planting in Hokkaido's forests in just one year. Usually, this takes two years, indicating that growth with WCM films could mean more cost-efficient plant production.

'This opens a large avenue of future development for next-generation agricultural and forestry engineering'

How a thin coated film could upgrade photosynthesis and feed 9 billion people
How the UV-to-red WCM film equipped with a Eu3+ works

"We think that the emitting wavelength of the material and coating thickness are important to control the balance of light for the plants," Shoji told IE.

"In future we hope to study the effect of these parameters and better understand how much customization is needed for different plant species."

In other words, the ability to freely control the amount of light of different wavelengths, like green and yellow, means the team now looks forward to investigating optimized WCMs for different plant types. Shoji described how this development opens a large avenue of future growth for next-generation agricultural and forestry engineering.

Besides, "We hope to study how changing the molecular structures of the luminescent materials on the film affects plant growth acceleration," revealed Shoji to IE.

Customizing the technology could help meet four UN sustainable development goals (SDGs)

It is hoped that the technology may one day be utilized to enhance food production in colder climates, where the days are short and the sun's rays are weaker, contributing to sustainable development goal 2 (SDG 2) — zero hunger.

The study also highlights additional SDGs the team believes the WCM could help achieve. These include SDG7 (affordable and clean energy), SDG9 (industry, innovation, and infrastructure), and SDG15 (life on land).

The europium (Eu3+) thin film, which operates in sunlight, is a promising candidate for sustainable and eco-friendly UV-to-red light WCM; i.e., it doesn't consume electricity, unlike farms and nurseries using LED devices.

From key understandings to observable gains

Developing a better understanding of the mechanisms involved in photosynthesis has been the subject of decades of study. For example, Hartmut Michel, Robert Huber, and Johannes Deisenhofer were jointly given the 1988 Nobel Prize in Chemistry "for the determination of the three-dimensional structure of a photosynthetic reaction center."

Naturally, this is all for a good reason; as this recent study shows, a better knowledge of how photosynthesis works may ensure the sustainability of our food supply in the future. Research like this, which could convert key understandings into observable gains in agricultural yield, indicates that we might soon start to see this strategy's benefits at scale. We'll keep you posted.