NewsMakers: Research

Increased CO2 Levels Are a Mixed Blessing for Agriculture

A new study by Peter Curtis, EEOB, suggests that rising levels of carbon dioxide in the atmosphere could be a boon for agricultural crops, as this greenhouse gas helps crop plants grow and reproduce more.

But that boon comes with a price, he says. Greater growth and reproduction may hurt the nutritional value of crops.

"If you're looking for a positive spin on rising CO2 levels, it's that agricultural production in some areas is bound to increase," Curtis says. "Crops have higher yields when more CO2 is available, even if growing conditions aren't perfect.

"But there's a tradeoff between quantity and quality. While crops may be more productive, the resulting produce will be of lower nutritional quality."

Nutritional quality declines because while the plants produce more seeds under higher CO2 levels, the seeds contain less nitrogen.

"The quality of the food produced by the plant decreases, so you've got to eat more of it to get the same benefits," Curtis explains. "Nitrogen is a critical component for building protein in animals, and much of the grain grown in the United States is fed to livestock.

Curtis and his colleagues analyzed eight different ways plants respond to higher CO2 levels: number of flowers; number of fruits; fruit weight; number of seeds; total seed weight; individual seed weight; the amount of nitrogen contained in seeds; and a plant's reproductive allocation, a measurement of a plant's capacity to reproduce.

Plants grown at higher CO2 levels had more flowers (an average of 19 percent more in the species studied); more seeds (16 percent more); greater individual seed weight (four percent more); greater total seed weight (25 percent more) and lower concentration of nitrogen in the seeds (a decrease of 14 percent) than those grown at current levels of atmospheric CO2.

Even though seed size increased, the amount of nitrogen in the seeds didn't. Nitrogen levels decreased by an average of 14 percent across all plants except cultivated legumes, such as peas and soybeans.

"That's bad news," Curtis said. "Nitrogen is important for building protein in humans and animals. If anything, plant biologists want to boost the levels of nitrogen in crops.

"A growing global population demands more food, but humans would have to eat more of the food to get the same nutritional benefits."

"Ecologically speaking, changes in the number of flowers, fruits and seeds and their nutritional quality could have far-reaching consequences," Curtis said. "Changes in the amount of nutrients in seeds could affect reproductive success and seedling survival. Such changes could also have long-term effects on ecosystem functioning."