An extensive study designed to simulate the growing conditions of the future has cast significant doubt on widely held assumptions about the impact of climate change on food production, suggesting that we will face significant crop failures far sooner than previously thought.
The study, which is published today in the journal Nature Plants, saw researchers from the University of Illinois conduct an eight year-long study of soybeans that were grown outdoors in a carbon dioxide-rich atmosphere. This was designed to mimic the higher atmospheric CO₂ concentrations that we are projected to experience by 2050.
It had been thought that the increased levels of CO₂ would balance future water shortages, by prompting the plans to reduce the size of the pores in their leaves and so reducing gaseous exchange with the atmosphere. This would reduce the amount of water the plants needed from the soil, resulting in crops that were only minimally affected by climate change.
“If you read the most recent Intergovernmental Panel on Climate Change reports and if you read the scientific literature on the subject for the last 30 years, the concluding statement is nearly always that elevated carbon dioxide will ameliorate drought stress in crops,” explained lead author Andrew Leakey, an associate professor of plant biology at the University of Illinois.
However, the study found a flaw in that premise, in that it only works in wetter growing seasons.
“[The theory] was consistent with what we saw with our own experiments the first four years, the relatively wet years,” added Leakey. “But when the growing seasons were hot and dry, that pattern broke down.”
The researchers created the CO₂-rich environment in real farm fields using a technology known as the Soybean Free Air Concentration Enrichment Facility. This featured sensors that that can measure wind speed and direction, prompting the regulated release of gases to simulate higher concentrations of CO₂.
This allowed the researchers to determine that plants grown in a hot, dry CO₂-rich environment needed more water than plants growing under the same conditions but with current atmospheric CO₂ levels; the opposite of what previous research had suggested.
“All of the model predictions up to this point were assuming that in 2050, elevated CO₂ was going to give us a 15% increase in yield over what we had at the beginning of this century,” Leakey said. “And what we’re seeing is that as it gets hotter and drier, that number diminishes to zero. No gain.
“What we think is happening is that early in the growing season, when the plant has enough water, it’s able to photosynthesize more as a result of the higher CO2 levels. It’s got more sugars to play with, it grows more, it creates all this extra leaf area. But when it gets dry, the plant has overextended itself, so later in the season it’s now using more water.”
The research has significant implications for the management of food security in the future, with soybeans being the fourth biggest food crop in the world by area harvested.
In addition to providing a valuable source of protein for nonmeat eaters, they are used in a wide array of foods, oils and sauces, particularly in East Asia where the crop has formed a significant part of the diet since at least 7,000 BC.
Soybeans are also used extensively for livestock feed, making their importance for food security even greater.