Future drought will offset benefits of higher CO2 on soybean yields.
An eight-year study of soybeans grown outdoors in a carbon dioxide-rich atmosphere like that expected by 2050 has yielded a new and worrisome finding: Higher atmospheric CO2 concentrations will boost plant growth under ideal growing conditions, but drought — expected to worsen as the climate warms and rainfall patterns change — will outweigh those benefits and cause yield losses much sooner than anticipated.
The new discovery, reported in the journal Nature Plants, contradicts a widely accepted hypothesis about how climate change will affect food production, said University of Illinois plant biology professor Andrew Leakey, who led the new research.
Under hot and dry conditions at elevated CO2, the plants in the SoyFACE experiments used more, not less, water than those grown under current atmospheric conditions, the researchers found.
"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.
Elevated CO2 and drought together also influence soybean’s ability to fix nitrogen through nodules formed on its roots.
Under elevated CO2 and drought, the number of beneficial nodules on the soybean roots increases, Leakey said.
"But what we find is that they put all these extra nodules on in relatively shallow soil layers.
And the nodules don’t work well when they’re in dry soil."
Intensifying drought eliminates the expected benefits of elevated carbon dioxide for soybean.