Scientists Are Trying to Grow Crops in the Dark
By Matt Reynolds, Wired.com, 04 July 2022
Powering plant growth with solar panels instead of photosynthesis could be a more efficient way of using the sun’s energy for food. But it’s not all good news.
We have a lot to thank photosynthesis for. Our entire existence, for a start. About 3 billion years ago, a group of microbes called cyanobacteria evolved a way to turn light and water into energy, releasing oxygen in the process. These microbes would eventually flood our atmosphere with oxygen—turning it from a toxic miasma of mostly nitrogen and carbon dioxide into the life-sustaining mix we have today. All of it—plants, humans, dogs, Netflix, ice cream—started with photosynthesis, more or less.
The same process is also right at the beginning of everything we eat. Plants use sunlight, water, and carbon dioxide to grow, and then humans either eat those plants directly or after they have become part of an animal, mushroom, or anything else we like to munch on. All of the energy that ends up in our bodies starts with sunlight captured by plants through photosynthesis. There’s just a tiny hitch in this system—plants are actually pretty bad at turning sunlight into growth. By some estimates, plants convert sunlight and carbon dioxide into new biomass at an efficiency as low as 1 percent.
Robert Jinkerson, a professor at the University of California, Riverside, looked at the lackluster efficiency of photosynthesis and saw an engineering problem. If we can squeeze more energy out of every square inch of sunlight, then we can reduce the overall amount of land we need to grow food. “Our ultimate goal is to transform the way that we think about how to produce crops and agriculture,” says Jinkerson. “If we can be more efficient with the area needed to produce the food needed for humanity, then we can turn agricultural lands back to natural lands.”
One way to do that might be to grow crops in the dark using electricity provided by solar panels, which are many times more efficient than plants at turning sunlight into energy. In a new scientific paper published in the journal Nature Food, Jinkerson and his colleagues describe using solar panels to power a process called electrocatalysis, which creates a liquid that algae, yeast, and plants can use to grow instead of sunlight.
The researchers used solar panels to run a machine that converts carbon dioxide, electricity, and water into acetate—a molecule that can be diluted in water and used to feed plants. They then fed this mixture to algae, yeast, mushrooms, and a selection of commonly grown plants, including cowpea, tomato, canola, and rice. The algae and yeast both grew pretty efficiently on the acetate mixture, which isn’t exactly surprising, as scientists already know that these species can eat acetate. What was more surprising was that the crop plants also consumed the acetate and grew, even though they were growing in complete darkness.
But before you shut away your tomato plants in a cupboard, a word of warning. Jinkerson and his colleagues only knew that the plants were eating the acetate because they dissolved them after they’d grown for a little while and analyzed them to see whether they contained any carbon molecules from acetate. But giving the plants enough acetate to grow on ended up proving toxic to them—so although plants can technically grow on acetate, they don’t exactly thrive on it.
This means that we’re a long way from being able to grow any common commercial crops in the dark. But this technology could be of interest for vertical farms, which already run up huge electricity bills on LED lights that power photosynthesis for their plants. Jinkerson thinks that if researchers can find a way to grow tomato plants that really thrive on acetate, it could be a much more energy-efficient way for vertical farms to divert electricity to acetate production instead of lighting.
But even if we could bring more tomato plants indoors, that wouldn’t necessarily free up much land to return to nature. The majority of agricultural land is used for pasture to graze animals or to grow feed for animals. A lot of the remaining land is used to grow commodity crops, such as wheat, soy, or corn, with only a relatively small amount of land used to grow fruits and vegetables. These commodity crops are extremely cheap to grow outside, so investing lots of time and money to grow them indoors doesn’t make a whole lot of sense. Growing plants in the dark might be useful in places where energy and space are scarce—like on a spaceflight to Mars—but it’s not suitable for most crops on Earth. (Jinkerson’s project was also one of the winners of the first phase of NASA’s Deep Space Food Challenge. For the next phase, the team will build a prototype food-growing device to share with the space agency.)
There are already lots of ways that we can use cropland more efficiently, points out Elizabete Carmo-Silva, a professor of crop physiology at Lancaster University in the UK. Reducing food waste, eating less meat, and burning fewer crops for biofuels all help us get more edible calories out of every hectare of land. And we shouldn’t write photosynthesis off yet, either.
“We have nothing else that provides oxygen and food at basically very little cost to us,” says Carmo-Silva. She’s currently working on a project to increase the photosynthetic efficiency of cowpea—an important crop in Africa and Asia. “If we really want to tackle the challenge of food security and have food security everywhere in the world, we need to address it with multiple solutions,” she says. Her team is exploring whether it’s possible to use breeding or gene-editing to make versions of cowpea that are 20 percent more efficient when it comes to photosynthesis.
Finding ways to improve photosynthesis rather than bypassing it altogether might end up having a bigger impact on the world, says Amanda Cavanagh, a plant scientist at the University of Essex in the UK. “For things like soybean or maize or wheat, our inefficient photosynthesis is likely still to be our best bet for realizing gains in those crops.”
But Jinkerson’s work also raises some tricky questions about the kinds of food people will accept. Much of the work on improving photosynthesis involves gene-editing plants, which is still a controversial technology in parts of the world—particularly in the EU. Which is more natural: a gene-edited plant, or one that has never seen a ray of sunlight? And if one day we manage to grow tomatoes in the darkness, Cavanagh says, would they still be as tasty as those grown in the open air? If Jinkerson’s prototype food-growing device works as planned, NASA astronauts might be the first to have an answer.