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Growing plants in the dark sounds like something out of science fiction, but a new breakthrough has brought it closer to reality.
The development could lead to new ways of growing food in a world wracked by climate change, researchers have said.
The electrocatalytic process allows plants – in this case green algae – to grow in the dark, powered by carbon dioxide, electricity and water.
Scientists have said that the new process is 18 times more efficient than natural photosynthesis at converting energy into food.
Photosynthesis has evolved in plants for millions of years to turn water, carbon dioxide, and the energy from sunlight into the foods we eat.
But the process is inefficient, with only about 1% of the sunlight energy ending up in the plant.
The technology uses a two-step electrocatalytic process to convert carbon dioxide, electricity and water into acetate, a form of the main component of vinegar.
Food-producing organisms then consume acetate in the dark to grow.
Robert Jinkerson, a University of California Riverside assistant professor of chemical and environmental engineering, who worked on the study, said: "With our approach we sought to identify a new way of producing food that could break through the limits normally imposed by biological photosynthesis."
Experiments showed that a wide range of food-producing organisms could be grown in the dark directly on the acetate-rich electrolyser output, including green algae, yeast and fungal mycelium that produce mushrooms.
Producing algae with this technology is approximately fourfold more energy efficient than growing it photosynthetically.
Yeast production is about 18 times more energy efficient than how it is typically cultivated using sugar extracted from corn.
Elizabeth Hann, a doctoral candidate in the university's Jinkerson Lab and co-lead author of the study, said: "We were able to grow food-producing organisms without any contributions from biological photosynthesis.
"Typically, these organisms are cultivated on sugars derived from plants or inputs derived from petroleum – which is a product of biological photosynthesis that took place millions of years ago.
"This technology is a more efficient method of turning solar energy into food, as compared to food production that relies on biological photosynthesis."
The potential for employing the technology to grow crop plants was also investigated.
Cowpea, tomato, tobacco, rice, canola and green peas were all able to utilise carbon from acetate when cultivated in the dark.
Marcus Harland-Dunaway, a doctoral candidate in the Jinkerson Lab and co-lead author of the study, said: "We found that a wide range of crops could take the acetate we provided and build it into the major molecular building blocks an organism needs to grow and thrive.
"With some breeding and engineering that we are currently working on we might be able to grow crops with acetate as an extra energy source to boost crop yields.
"By liberating agriculture from complete dependence on the sun, artificial photosynthesis opens the door to countless possibilities for growing food in a world battered by extreme weather caused by anthropogenic climate change."
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