Why Plants Waste Almost All the Solar Energy They Receive

Introduction: the disappointing efficiency of photosynthesis

A vital process, but surprisingly inefficient

Photosynthesis is often presented as one of the most remarkable mechanisms in the living world, capable of turning sunlight into chemical energy that plants can actually use. It underpins nearly all life on Earth, supplying both the oxygen we breathe and the organic matter that feeds every food chain on the planet.

This process unfolds inside chloroplasts, tiny structures found in plant cells, where captured light is used to assemble sugar molecules from carbon dioxide and water, through a sequence of biochemical reactions of extraordinary molecular complexity.

Yet despite its critical importance, this process is surprisingly inefficient from an energy standpoint. On average, plants convert only 1 to 2 percent of the light energy they receive into chemical energy they can actually use for growth, an efficiency rate that often surprises the general public, who tend to assume nature is optimized to perfection.

A considerable gap between theoretical potential and reality

Scientists estimate that the maximum theoretical efficiency of photosynthesis, under perfectly optimized conditions, could reach roughly 11 percent of available solar energy. But in the reality of agricultural fields and natural ecosystems, the overall achievable efficiency sits closer to 3 to 6 percent, once every inevitable loss in the biological system is factored in.

This considerable gap between theoretical potential and what is actually observed on the ground has pushed many researchers to ask whether it might be possible to directly intervene in the photosynthetic machinery of plants to improve this efficiency, with potentially major consequences for global agriculture and the food security of billions of people.

Closing even part of this gap would represent a considerable leap forward for global agricultural production, without requiring more farmland, fertilizer, or irrigation water, resources already under heavy strain in many regions of the world.

Where all that solar energy actually disappears

Losses at every stage of the process

To understand why the efficiency of photosynthesis stays so low, you have to follow the path of light energy from the moment it hits the leaf all the way to its final transformation into sugars and other organic compounds the plant uses to grow and reproduce.

A significant portion of incoming light is simply reflected off the leaf's surface or passes straight through the plant tissue without being absorbed by the photosynthetic pigments, chiefly chlorophyll, which is only effective at capturing certain precise wavelengths of the visible light spectrum.

Another significant share of the available solar energy arrives at wavelengths that plant pigments simply cannot use, such as certain bands of infrared radiation, which further reduces the amount of energy actually available for the photosynthetic reaction itself.

Additional losses then occur during the many biochemical conversion steps, each of which inevitably comes with some partial dissipation of energy as heat, an unavoidable phenomenon in virtually every energy transformation process known in physics and biology.

The costly role of photorespiration

One of the most significant sources of loss goes by the name photorespiration, a biochemical mechanism researchers sometimes describe as pure energy waste, which occurs when the enzyme responsible for fixing carbon accidentally captures oxygen instead of carbon dioxide.

This mechanism forces the plant to spend considerable energy recycling the toxic compounds that result, an expenditure that, according to scientists' estimates, can account for as much as a quarter of the energy potentially available in certain major crops such as soybeans or wheat grown at large scale.

Reducing this energy waste tied to photorespiration has therefore become one of the preferred targets of research programs seeking to artificially improve the photosynthetic efficiency of cultivated plants around the world.

The RIPE program, funded by the Gates Foundation

A clearly stated mission: reinventing photosynthesis

It is precisely to tackle this problem that the RIPE research program was created, with a mission to advance the science and engineering of photosynthesis by pursuing fundamental discoveries capable of opening new paths toward better agricultural yields and greater resilience to environmental stress.

This program is led by researcher Stephen Long at the University of Illinois, and brings together a broad international consortium of partners, including the Australian organization CSIRO, Lancaster University, the University of California, Berkeley, the University of Cambridge, the University of Essex, along with several specialized American agricultural research centers.

Massive funding from philanthropy

Founded in 2012 thanks to an initial grant of 25 million dollars spread over five years, the RIPE program was first funded by the Bill and Melinda Gates Foundation, before receiving an additional reinvestment of 45 million dollars in 2017, coming both from the foundation itself, the Foundation for Food and Agriculture Research, and the United Kingdom's Department for International Development.

In 2018, the Gates Foundation injected another 13 million dollars into the program, before a new round of 34 million dollars, spread over four years, was granted in 2022 by the organization Gates Ag One, specifically earmarked to extend the research to crops such as cowpea and soybean, which are particularly important for the food security of many developing countries.

This level of philanthropic funding, rare in the field of fundamental research in plant biology, reflects the strategic importance its funders place on improving photosynthetic efficiency as a potential response to the global food challenges of the coming decades.

Yield gains already measured in the field

A landmark study published in the journal Science

In 2019, a study published in the prestigious journal Science demonstrated that it was possible to increase the yield of certain crops by nearly 40 percent by genetically modifying the recycling pathways linked to photorespiration, a result considered a major breakthrough and widely covered across the international scientific community.

This experiment, conducted over two consecutive years under real field-growing conditions, showed that the genetically modified plants grew significantly taller and produced roughly 40 percent more biomass, largely thanks to stems nearly 50 percent bulkier than those of unmodified control plants.

To put that figure in perspective, conventional plant breeding techniques typically deliver annual gains of only about 1 percent, which makes a yield jump of this magnitude, achieved through a single targeted genetic intervention in these crops, all the more remarkable.

Complementary results on protection against excess light

Another approach explored by RIPE program teams involves acting on plants' photoprotection mechanisms, the natural systems that dissipate excess light as heat to prevent damage to the photosynthetic apparatus during overly intense sun exposure.

By genetically adjusting the speed at which plants switch off this protective mechanism once light levels drop again, for instance in the shade of a passing cloud, researchers achieved yield gains of between 14 and 20 percent in repeated field trials, marking one of the first concrete demonstrations that photosynthesis can be modified to produce better agricultural yields.

A direct stake in global food security

Intensifying demographic pressure

According to estimates from the Food and Agriculture Organization of the United Nations, global food production will need to increase by roughly 70 percent by 2050 to keep pace with expected population growth and shifting consumption habits across many regions of the world.

Facing this considerable pressure, and given the physical limits imposed by the availability of farmland and freshwater resources, improving the photosynthetic efficiency of existing crops appears to be one of the few paths capable of generating productivity gains large enough without requiring a massive expansion of agricultural land.

One solution among others, not a single answer

Researchers with the RIPE program nonetheless insist that improving photosynthesis is only one of several approaches that must be combined to meet the global food challenge, alongside others such as reducing food waste, improving farming practices, and fighting crop pests and diseases.

This combined approach remains particularly promising, however, because it directly targets the fundamental biological limit of all agricultural production: the amount of solar energy a plant actually manages to convert into material useful for feeding people and animals.

Conclusion: a potential still largely untapped

What recent advances reveal

The work carried out by the RIPE program and by other research teams around the world clearly demonstrates that the low natural efficiency of photosynthesis is not a fixed biological fate, but rather a trait that can be significantly improved through targeted genetic interventions rigorously tested in the field.

The gains already observed, whether the 40 percent achieved by correcting losses linked to photorespiration or the 14 to 20 percent tied to optimizing photoprotection, far exceed anything traditional plant breeding methods could offer over a comparable period.

A long road remains before widespread adoption

There nonetheless remains a considerable road to travel before these genetically optimized crops are widely adopted by farmers around the world, particularly given the varied regulatory frameworks governing genetically modified organisms from one country and continent to another.

This research into photosynthetic efficiency nonetheless illustrates a concrete, already partially validated scientific path toward addressing one of the greatest challenges of the coming century: feeding an ever-growing global population without further depleting our planet's limited resources.

By Maxime Marquette, columnist

Columnist's transparency note

How I approached this guide

This guide draws on the RIPE program's own public materials from the University of Illinois, along with peer-reviewed coverage of the 2019 Science study and subsequent field-trial results on photoprotection. I am not a plant biologist, and I have deliberately stuck to figures the researchers themselves have published rather than speculating about yield gains that have not yet been demonstrated in the field.

I also chose to spend real space on the funding history behind RIPE, because I think readers deserve to know that a discovery this consequential for global food security has been shaped, in large part, by a small number of philanthropic funders making a long-term bet on basic plant science rather than a quick commercial return.

Why I kept the regulatory caveat front and center

Genetically modified crops remain a politically and legally sensitive subject in many countries, and I did not want this guide to read as an unqualified endorsement of a technology still facing very different regulatory paths depending on where a farmer happens to live. The science behind these yield gains is solid, but adoption is a separate question, shaped as much by policy and public trust as by laboratory results.

Sources

Primary sources

RIPE — Realizing Increased Photosynthetic Efficiency, University of Illinois — official program page

Nature — Photosynthesis: scientific publications on photosynthetic efficiency

PNAS — Proceedings of the National Academy of Sciences, research on plant biology

Secondary sources

Futura Sciences — Accessible analysis of photosynthesis and agriculture

Sciences et Avenir — Coverage of advances in plant biology and agronomy

National Geographic — Reporting on global food security and sustainable agriculture