Climate change could lower the nutritional quality of Midwestern soybeans, according to a new study from SoyFACE researchers. The researchers found that soybeans grown under predicted future levels of carbon dioxide (CO2) had lower concentrations of certain important nutrients, including iron and calcium.
This does not mean there will be an imminent breakdown of our food system, Anthony Digrado said, a plant biologist at the University of Illinois and the first author of the study. But, the study does warn that yield should not be the sole priority as global CO2 emissions continue to rise.
“The nutrient declines we saw were relatively minor, but this is something we need to keep an eye on,” said Dr. Digrado.
The study was published in the journal Global Change Biology in Feb 2024.
Early on at SoyFACE, researchers found that raising CO2 levels had a positive impact on the yields of plants that do C3 photosynthesis, such as soybean. Plants that do C3 photosynthesis are relatively inefficient at using CO2, so when more CO2 becomes available, the plants perform better. For soybean, more CO2 equals more yield.
However, scientists were quick to check if there was a catch, and trials began on the effects of CO2 on crop nutritional quality. One of the most influential studies in this field, published in Nature in 2014, found that legumes such as soybeans had lower zinc and iron content when grown under future CO2 levels. This study certainly drew attention to the problem, but the researchers still had one very big question- why exactly was this happening?
This question may already have been answered by a team of scientists back in 2004. Their study, published in the Journal of the American College of Nutrition, found that the nutritional content of common garden crops had been dropping since the 1950s. The scientists suggested that this was because farmers had been adopting newer, higher-yielding cultivars.
The idea that high-yielding crops have lower nutritional quality is called the “dilution effect.” Higher-yielding cultivars get most of their yield boost from increased carbohydrates. When this happens, the other nutrients get diluted.
To test the dilution effect theory for CO2, Dr. Digrado and his colleagues compared the nutritional responses of two different soybean cultivars. One of the cultivars, Loda, has well-established yield increases under high CO2, while the other cultivar, HS93-4118, has less of a yield response.
An earlier group of researchers grew Loda and HS93-4118 soybeans at SoyFACE from 2004 to 2008 under high CO2 levels and then measured the seeds’ nutritional contents. Dr. Digrado and his colleagues used a type of statistics called path analysis on this dataset to see if nutrient declines were because of the dilution effect or not.
The researchers found that both cultivars had less of certain nutrients under high CO2, including iron, zinc and calcium. They also found that Loda, the high-yielding cultivar, had a stronger “path” between CO2 and yield. This meant that the nutrient declines were because of higher yields i.e., the dilution effect.
However, the scientists observed that certain nutrients such as aluminum and cobalt declined but did not have a “path” between CO2 and yield. In other words, it was not the dilution effect that caused these nutritional declines.
These nutritional declines could have been because of altered root growth or water uptake, but more research is needed. “Untangling these mechanisms can be complicated and takes great efforts,” said Mary Durstock, a researcher from the University of Illinois who specializes in crop responses to CO2, but who was not involved in the study.
Thankfully, we still have time to figure out exactly what is going on. “We’re going to be seeing these simulated CO2 levels in 70 years, not tomorrow,” Dr. Digrado said.
However, the study still provides valuable insight into the potential trade-off between yields and nutritional quality. “Higher yields will always be a target for crop breeding, so these findings are relevant to us right now,” Mary Durstock said.
Story sources: Dr. Anthony Digrado; Mary Durstock
Written by Megan Allen