The sun sets outside with the high temperatures of the 80s where they will stay most of the night, several varieties of potted rice plants growing in two sections of a greenhouse on the roof of Arkansas State University’s Institute for Biological Sciences.
In one section, the greenhouse temperature is almost the same as outside; in the other it is upgraded with 4C. Here, a dry, fragile flower hangs from one of the plants, its growth stunted by the heat.
This is the highlight of the day for the research project of metabolic engineering professor Argelia Lorence and her team. Because the climate crisis is pushing daytime temperatures to record levels, nighttime temperatures are rising significantly faster. This is a big problem for humans and animals trying to cool their bodies at night. But it’s also a crisis for plants, which have fewer defenses at night and pose a major threat to the global food system.
“Because of how photosynthesis works, plants need cooler temperatures at night. And there are processes that are currently being disturbed,” says Lorence.
Every 1 degree increase in night temperature can cause wheat yield to decrease by 6% and rice yield by up to 10%. Warmer nights can also affect quality, making the rice chalky and less flavorful, and even altering the nutrient composition.
Lorence and his team at Arkansas State University’s Institute of Biological Sciences are part of the race to figure out how to create rice varieties that are the main food source for billions of people around the world and a vital crop for farmers worldwide. fast changing climate.
In 2019, rice growers began a two-year experiment at RiceTec’s experimental sites in Harrisburg, Arkansas, applying heat stress to different rice crop varieties. The team built six customizable greenhouses that allow them to grow rice in field conditions during the day and create higher temperatures at night. The greenhouses were built from a kit that was put together from “lego-like” pieces, including walls that slide back and forth and a roof that retracts to expose the plants to the air.
The researchers hand-sowed 1,920 seed packets of 320 varieties of rice in each greenhouse, waiting for what Lorence called “the most sensitive developmental stage in a rice plant” to flower.
At night, during the two weeks of the flowering phase, an automated system raised the temperature in three of the greenhouses by 4C relative to the temperature in the other three control greenhouses – which was in line with the outdoors. This warming was hot enough to have a net effect on the plants, but not severe enough to directly kill them all.
The researchers commuted to and from the field every day during the experiment, manually opening and closing the plastic roofs in the mornings and evenings. In late summer, in August and September, the team collected 30,000 plants and then took them back to campus for researchers to analyze which cultivars did better and why.
Lorence’s lab in Arkansas, facing the Mississippi River, the heart of the state’s $6 billion rice industry, is part of a larger project called the Wheat and Rice Refractory Center (WRCHR) to understand the effects of nighttime temperatures on crops. ), a collaboration that also includes the University of Nebraska-Lincoln and Kansas State University.
Krishna Jagadish, a founding researcher on the WRCHR project and now a professor at Texas Tech while in Kansas State, said one reason the increase in nighttime temperatures has had a worse effect on crops is that plants don’t have as many defense mechanisms at night. .
They may use their stomata — tiny pores on the leaf’s surface — to protect against heat during the day, but most of them are closed at night, Jagadish said. Plants also have nowhere to hide from the heat of the night, unlike during the day when shade from crop canopies allows parts of the plant to escape the heat.
The research collaboration helps develop new wheat and rice varieties. “We can make these available to growers. “Then growers can then get farmers to start tying it to the soil,” said Harakamal Walia, an agricultural engineer at the University of Nebraska-Lincoln who led the project.
His lab took images of 400 rice varieties grown individually in a high-tech greenhouse at each stage of development and analyzed the images to identify changes caused by heat stress. They have already identified a gene that regulates grain width in rice: fie1. Varieties with this gene were less sensitive to high nighttime temperatures. “They were able to sustain the grain weight even when the nights were warmer,” Walia said.
This process is slightly more complex in wheat and more difficult to analyze and rank because it has six separate sets of chromosomes compared to the two in rice. Less research has been done to determine the effect of higher nighttime temperatures on wheat and which traits may lead to greater resilience, Jagadish said. His old lab in Kansas State tried to fill that gap.
The State of Kansas, which originally developed the greenhouses used by Lorence’s team, used them to conduct similar experiments on wheat in 2019. The research team found that for field-grown wheat, high nighttime heat stress resulted in lower yields, lower grain weight, and lower grain weight. reduction in starch and protein.
In Arkansas, Lorence’s team is now deep in the painstaking process of analyzing two years of data from their greenhouse. This July afternoon, the lab is bustling with a dozen researchers busy placing rice granules in trays for analysis, writing and running scripts for image analysis, or watering the rooftop plants.
Originally from Mexico, Lorence put together an international team of scientists. Crop physiologist and doctoral student Cherryl Quiñones, originally from the Philippines, is researching how vitamin C can help plants become more resilient. Like quiñones, Kharla Mendez, a doctoral student who came to Arkansas State from her hometown of the Philippines, examines how sugar and starch can give plants more protection. Karina Medina, a biotechnology postdoctoral researcher and laboratory director from Mexico, is using robotic imaging on rice seeds to understand how high nighttime temperatures affect their weight, size and quality.
As her researchers gather their data, Lorence sends them to Gota Morota, a geneticist at Virginia Tech, who conducted analyzes to isolate genes that appear to be associated with rice’s high nighttime tolerance.
WRCHR hopes that the varieties, genes and phenotypes it has isolated can be used by rice and wheat growers to create new crop varieties and then passed on to farmers to ensure their fields are producing at peak capacity even as temperatures rise.
The researchers hope that breeders will be able to create rice and wheat varieties that can save the world’s food supply by combining genes that are resistant to a range of stressors (not only high nighttime temperatures, but also drought, salinity and others). consistent as the effects of the climate crisis continue to worsen.
The effects of high nighttime temperatures on rice are already here. An intense heatwave that swept Bangladesh in April 2021 destroyed tens of thousands of hectares of rice crops, affected 300,000 farmers and caused nearly $40 million in losses.
“When we look at parts of Bangladesh or eastern India, we find that these stressors and [high night-time temperatures] “It’s been happening alone for over a year and a half,” said Neşe Sreenivasulu, a researcher at the International Rice Research Institute, who also studies the effects of high nighttime temperatures on rice. Sreenivasulu’s research found that Bangladesh and southern and eastern India are already vulnerable to rising temperatures day and night.
“These stresses that affect crop yield and quality will become more and more frequent,” said Medina, director of the Arkansas State lab. “We must act now to develop the varieties we will need in the future.”
The work to understand and develop these heat-tolerant plants is just beginning. “We’re just starting to figure out what genes might help us develop better crops in the future,” Lorence said. Said. “There are still so many genes to be discovered, so many mechanisms still to be understood.”