How does rising CO2 affect crop production?

For decades, a network of 14 research facilities located across five different continents has been working to predict the impacts that future CO2 levels will have on crop production. The research involves “Free-Air Concentration Enrichment” (FACE) experiments, which are real-world field surveys designed to study the environmental factors that impact crop growth and yield.

Based on the analysis of 30 years of FACE data, researchers have found some discouraging details of how global crop production may be impacted by rising CO2 levels.

Study co-author Lisa Ainsworth is a research plant physiologist with the U.S. Department of Agriculture, Agricultural Research Service (USDA-ARS). 

“It’s quite shocking to go back and look at just how much CO2 concentrations have increased over the lifetime of these experiments,” said Ainsworth.”We are reaching the concentrations of some of the first CO2 treatments 30 years back. The idea that we can check the results of some of the first FACE experiments in the current atmosphere is disconcerting.”

The study was focused on two groups of plants: C3 plants such as soybeanand rice, which are less efficient at converting CO2 and light into energy through photosynthesis; and C4 plants, such as corn and sugarcane, which are up to 60 percent more efficient at using CO2 and light for energy. 

Many commercial growers elevate CO2 levels in greenhouses to boost photosynthesis and crop production among plants like tomatoes, peppers, and cucumbers.

In the current analysis, the researchers found that CO2 levels expected at the second half of this century could increase C3 crop production by 18 percent with adequate nutrients and water.

Study co-author Stephen Long is a professor of Crop Sciences and Plant Biology at the University of Illinois and a member of the Carl R. Woese Institute for Genomic Biology.

“So should we anticipate a bounty as CO2 rises?” said Professor Long. “Sadly not because rising CO2 is the primary cause of change in the global climate system. The anticipated 2° C rise in temperature, caused primarily by this increase in CO2, could halve yields of some of our major crops, wiping out any gain from CO2.”

While CO2 could increase crop production, the experts found that the resulting crops would lose some critical components of their quality, such as nutrient and protein content. The study also revealed that major food crops become considerably more vulnerable to pests and diseases when exposed to higher levels of CO2.

“Lots of people have presumed that rising CO2 is largely a good thing for crops: assuming more CO2 will make the world’s forests greener and increase crop yields,” said Ainsworth. “The more recent studies challenge that assumption a bit. We’re finding that when you have other stresses, you don’t always get a benefit of elevated CO2.”

Looking on the bright side, the study authors noted that there is sufficient genetic variation in major crops to overcome some of the negative effects of higher CO2 levels and to capitalize on the yield benefits. 

“Where genetic variation is lacking, there are some bioengineering solutions with one already demonstrated to prevent yield loss when the temperature is raised with CO2,” explained Professor Long. “But, given the time taken to develop new crop cultivars, this potential could only be realized if we start now.”

“We are driven by a motivation to prepare for the future and to identify the traits that are going to be important for maximizing this CO2 response while dealing with the aspects of global change that may drive down yields,” said Ainsworth. “The last 15 years have taught us to account more for the complex interactions from other factors like drought, temperature, nutrients, and pests.”

According to Ainsworth, researchers should explore a wider variety of crops and genotypes as well as different management practices, such as seeding density, tillage, and cover crops, to find solutions that are less burdensome on the environment. In addition, it would be greatly beneficial to make the FACE data on crop production more accessible.

“We don’t have a formal database of all of the FACE results from the last two decades of research. There’s an opportunity to put all of the information together in one place and make it openly accessible for everyone to use and to encourage more people to use the data to think about solutions.”

“The ideal solution will be that we dramatically decrease our release of CO2 into the atmosphere and quickly achieve carbon neutrality,” said Professor Long. “But we also need to take out an insurance policy against this not being achieved. That is, we need to breed and engineer future-proof crops and systems that can be sustainable and nutritious under the combined changes in atmospheric composition and climate to help realize the goal of zero hunger.”

The study is published in the journal Global Change Biology.

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By Chrissy Sexton, Earth.com Staff Writer