Climate scientists are predicting that CO2 will increase to at least 550 parts per million (ppm) well beyond the current 410 ppm today. This will have both a positive and negative effect on the major agricultural crops such as wheat, rice, and soybeans that we use to feed both people and animals.

Depending on the crop, plant yield per acre will increase by 40-60%. But scientists are also discovering that the nutrition will decrease by approximately 10% (depending on the mineral or micronutrient) as the yield increases.

How is the effect of CO2 on crops determined?

FACE (Free Air Carbon Dioxide) experiments are the methodology used to compare crops with today’s CO2 of approximately 400ppm with an increase to 550 or 600 ppm. One crop will have enriched air, otherwise known as eCO2, pumped through sprinkler-like devices every few seconds and the other crop will rely on the CO2 currently available in the air.

Free-air carbon dioxide enrichment (FACE) experiments use controlled atmospheric concentrations of carbon dioxide in the field — a more realistic representation of increased levels of carbon dioxide in the atmosphere. Photo: David F. Karnosky

Nature published a meta-analysis of wheat, soybeans, maize, sorghum, rice, and field peas from Australia, China, Japan, and the United States. There was an overall 50% increase in yield and an approximate 10% decrease in nutrients, specifically zinc, iron, and protein.

Rob Norton, Director, IPNI Australia and New Zealand, has done several FACE studies to understand the effect of changes in water, temperature, and with eCO2 on wheat. He and his team found that the wheat grain yield increased by 50%. They also confirmed that higher yields dilute the nitrogen. Nitrogen produces protein in the plant. So when nitrogen is diluted, protein is diluted. Normally, wheat is 15.5% protein and under the enriched CO2 environment the protein percentage dropped to 13.5%.

Faster growth does not necessarily mean more zinc, iron, or protein. When grain yield is increased a ‘dilution problem’ occurs. Think of dropping a cube of sugar into a glass of water. Then add more water, the sugar becomes diluted. This is similar to what happens when plants grow due to an increase in CO2. Interestingly enough, the chart below shows that this phenomenon occurred even during the Green Revolution when farmers adopted fertilizer and high-yielding plants.The opposite effect can also occur. If you evaporate the sugar water, you have a sugar concentrate. The same is true with a reduction in yield. While there would not be the quantity of grains, oilseeds, or rice, the nutritional quality would increase.

It is not just CO2 which affects the nutrient concentration, it can be the plant breed, or even the amount of fertilizer used, which can also increase the yield.

Some fruits and vegetables are also slightly at risk from CO2 increases.

A group of scientists from Germany, Australia, and China also looked at a meta-analysis consisting of 57 observations – primarily focusing on lettuce, tomatoes, and potatoes.  They discovered that enriched CO2 increased concentrations of fructose, glucose, antioxidant capacity, total phenols, total flavonoids, ascorbic acid, and calcium but decreased protein, nitrate, magnesium, iron, and zinc.

Will this decline in nutrients affect your diet?

If you are reading this, you probably have enough of a varied diet that you are able to get your nutrients through the 2000 or so daily calories you consume. In addition, while there could be a drop in crop nutrition, it is not significant enough to make you run to the vitamin store.  However, if rice is 1/4^th of your diet, then this is an issue because this means a diversified diet is not available to you. As you can see below, one cup of rice or one slice of bread is not a significant source of protein, iron, or zinc.

How can we adapt food nutrients to an increase in CO2?

Now that it is becoming better understood how CO2 affects plants, researchers are studying how plant genetics can help them adapt. Plant biotechnology can enhance photosynthesis with a range of temperature, water, and CO2 so we can adapt to a higher carbon world. Biofortified crops will continue to be important for those who heavily depend on wheat and rice as a large portion of their diet.