Alcohol slakes the thirst of plants threatened by climate change
Few things feel worse than waking up to a nasty hangover: alcohol suppresses the release of an important hormone that keeps you from being dehydrated, leading to fatigue and headaches.
However, as counterintuitive as it sounds, alcohol has the opposite effect on plants.
A recent study published in Plant & Cell Physiology shows that pre-treating soil with ethanol significantly enhances crop plants’ drought tolerance — without genetic modification. The stakes are high for climate resilience in food systems. Some of the most economically stressed regions in the world face famine and displacement due to climate-driven heat and drought trends: weather extremes drove food insecurity for some 16 million people in 2020. Even the U.S. is not immune: In Kansas, the recent winter wheat harvest fell by over 25% due to drought; the Colorado Water Conservation Board estimates that the state could lose up to 700,000 acres of irrigated agricultural land (20%) by 2030 without better water conservation measures.
Plants produce ethanol when deprived of water, so the team, led by Motoaki Seki of the RIKEN Center for Sustainable Resource Science in Japan, hypothesized that proactively giving ethanol to plants such as wheat or rice would protect them from drought. The team grew seedlings for about two weeks with ample water. Then they treated soil with an ethanol solution for three days, followed by water deprivation for two weeks.
Ethanol priming changed the activity of hundreds of genes. The genes caused plants to accumulate drought-tolerant amino acids and sugars, which regulate photosynthesis. Plants also closed their stomata, or leaf pores, preventing evaporation from leaves and retaining more water than plants not treated with ethanol. About 75% of wheat and rice plants treated with ethanol survived the simulated drought, compared with under 5% for untreated plants. It did not take much ethanol to show positive effects; a dilution of about 0.3% (like pouring one teaspoon of ethanol into seven cups of water) was optimal for wheat.
The team then used Arabidopsis, a non-crop plant often used for research, to learn why ethanol had these effects. They found that plants treated with ethanol released ABA, a stress hormone that tells plants to close their stomata and activate drought-related genes.
But surviving a drought is not the same as thriving in a drought, and the study did not explore grain yields. “The mechanism used to improve survival in this paper is clear: it’s a decrease in stomatal conductance,” says François Tardieu, the Research Director of the French National Institute for Agriculture, Food, and Environment. Tardieu notes that it takes entirely different mechanisms and genes to improve survival than it does to increase grain yield.
Another question for further research is how ethanol affects plants in outdoor light. The study applied 100 μmol of light to the plants; Tardieu likens this to driving at twilight when cars’ headlights are coming on. While 100 μmol is fine for growing seedlings, a wheat field needs about 2,000 μmol of light (equivalent to full sun) to be productive. Because the amount of light strongly determines transpiration rates, ethanol could impact plants differently in bright outdoor lighting. The light question is crucial, as there is a strong association between light and crop yields.
Extensive research is needed to answer such questions and to determine whether ethanol confers benefits on grain yields. “This is a major challenge, not just ‘check,’” says Tardieu. “You need to test it in many fields, with different genotypes, at least three years of work with a good budget.” A budget for this type of study can be in the millions of Euros.
Tardieu cautions that the timing of crop priming would be critical for crops, whether using ethanol or another agent. Farmers priming plants to close their stomata should likely avoid doing so during flowering, “a very fragile time” for most staple crops, or during the early stages of growth. He says a better time is during the late stages of grain filling.
Another application of priming could be weather-based. “You know the forecast, and the plant doesn’t. If you have three days with very high evaporative demand, perhaps it is not worth spending all this water just for three days. So why not tell the plant: ‘You should close your stomata, and next week you begin again.’ This is fine, as long as it’s temporary,” says Tardieu.
If future research shows that ethanol priming is practical in the field, its simplicity and low cost could make it accessible to low-resourced farmers. Farms could produce ethanol locally (many developing nations already use biodigesters), and ethanol is potentially more affordable than genetically-modified seeds.
The drought paper comes on the heels of another by Dr. Seki’s team, demonstrating that plants, including lettuce, can thrive in extreme heat up to 50 °C (122 °F) for 3 hours when primed with ethanol in lab and field tests. The difference in the survival rate of Arabidopsis was striking (70% with ethanol; 10% without). Lettuces grew three times heavier in extreme heat with ethanol treatment than those without it. The lettuce results are more farm-ready than the grain results, as the heat study showed an actual increase in yield.
“We think that adding ethanol mitigates the stress and improves the growth of lettuce in a harsh temperature environment,” says Seki. The team is also testing the heat tolerance of other vegetables.
The Ethanol Issue
Ethanol has been touted by some as a more sustainable alternative to gasoline but receives increasing pushback. Studies have found that the average carbon dioxide emissions from ethanol production and consumption are about 20 percent lower than those of gasoline, while the U.S. Department of Agriculture contends that they’re about 40 percent lower. But as the Russo-Ukrainian war reminds us, the corn grown to produce ethanol occupies fields that could otherwise feed people and increases reliance on fossil-fuel-based fertilizers. Yet, while ethanol used as a vehicle fuel does little to alleviate food insecurity, ethanol used to treat crops just might.
People in drought-affected regions still need fruits, vegetables, and grains. If such crops had to be trucked or flown in, the food-miles emissions could easily outweigh those of ethanol production. “Global freight transport associated with vegetable and fruit consumption contributes 36% of food-miles emissions—almost twice the amount of greenhouse gases released during their production,” according to a June 2022 study in Nature Food. Surprisingly, global food-miles emissions for fruits and vegetables (1.06 gigatons of carbon dioxide equivalent) outweigh those of meat (0.11 gigatons); that’s primarily because more produce than meat by raw weight is shipped. Grains also contribute significantly to global food miles.
Mengyu Li, a Postdoctoral Fellow at the University of Sydney’s Center for Integrated Sustainability Analysis and a lead author of the food-miles study, says that truck and air transportation are the two most carbon-intensive transportation modes. Transporting food to drought-stricken regions around the globe has an enormous carbon footprint. Reducing food-miles emissions requires “the engagement of different actors at different supply-chain stages,” she says. In other words, everything matters, and local food is part of the solution.
And ethanol can be produced from crop waste, making it more sustainable. New research by the Agricultural Research Service of the USDA identified a yeast, Clavispora NRRL Y-50464, that produces ethanol more cost-effectively than the industry standard yeast, Saccharomyces cerevisiae. Clavispora makes it easier to use non-corn materials like grasses and crop residues to generate ethanol. The new yeast yields more ethanol faster than standard yeast and tolerates temperatures up to 39 C (102 F).
Suppose we diverted just a fraction of biofuel ethanol to treat crops–or better yet, derived ethanol from waste. More people would have access to local food, fewer byproducts would rot in fields (releasing methane, a powerful greenhouse gas), and less fuel would be needed to transport crops. It’s likely that net carbon emissions would decrease, a boost for efforts to slow climate change. But all this hinges on whether ethanol priming works in agricultural conditions.
Ethanol has the potential to help crops survive in a changing climate and improve produce yields in the heat. But science is still far from determining whether ethanol will increase grain yields on farms experiencing drought. In the meantime, Tardieu suggests that farmers could use different crop strains depending on conditions. For example, one strain of wheat might do best in a drought-prone field with shallow soil, but another type might yield more grain in a wetter field across the road. “Farmers know how to do that,” he says.
Correction: A previous version of the article misstated the global food-miles emissions of fruits, vegetables, and meat. We apologize for the error.