Increasing Levels of CO2 Results in Less Nutritious Crops

Elevated CO2 levels cause mineral deficiency in plants resulting in less nutritious crops.

For years, one of the only possible bright sides of increasing levels of atmospheric carbon dioxide (CO₂) seen by scientists is enhanced photosynthesisPhotosynthesis is how plants and some microorganisms use sunlight to synthesize carbohydrates from carbon dioxide and water.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>photosynthesis. After all, plants use carbon dioxide for photosynthesis, so it was expected that higher levels of the greenhouse gas will lead to more productive plants. However, this effect may be less than expected because elevated levels of CO₂ make it difficult for plants to obtain the minerals necessary to grow and provide nutritious food. This is explained by scientists from the Institute for Plant Science of Montpellier in France in a review published on November 3 in the journal Trends in Plant Science.

“There are many reports in the literature showing that the CO₂ levels expected at the end of the twenty-first century will lead to a lower concentration of nitrogen in most plants, mainly affecting the protein content in plant products,” says first author Alain Gojon. “It is very important to understand why growing plants at elevated CO₂ has such a negative effect on the protein content of most staple crops and the future of food.” Gojon is the research director of France’s National Research Institute for Agriculture, Food and the Environment.

Plants use photosynthesis to incorporate CO₂ into sugars that they derive their energy from. However, photosynthesis does not provide plants with the key minerals they need to grow. For most plants, these minerals, such as nitrogen, phosphorus, and iron, are picked up from the soil through their root systems. Nitrogen is particularly important as it is a key building block for the amino acids<div class="cell text-container large-6 small-order-0 large-order-1">
<div class="text-wrapper"><br />Amino acids are a set of organic compounds used to build proteins. There are about 500 naturally occurring known amino acids, though only 20 appear in the genetic code. Proteins consist of one or more chains of amino acids called polypeptides. The sequence of the amino acid chain causes the polypeptide to fold into a shape that is biologically active. The amino acid sequences of proteins are encoded in the genes. Nine proteinogenic amino acids are called "essential" for humans because they cannot be produced from other compounds by the human body and so must be taken in as food.<br /></div>
</div>” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>amino acids that plants use to make proteins.

Not only does a nitrogen deficiency mean that a plant will have difficulty building its tissues, but also that it will provide less nutrition to humans. “What is clear is that the nutrient composition of the main crops used worldwide, such as rice and wheat, is negatively impacted by the elevation of CO₂. This will have a strong impact on food quality and global food security,” says corresponding author Antoine Martin, researcher of the French National Centre for Scientific Research.

“Two main nutrients that are essential for human nutrition may be affected by this phenomenon,” adds Gojon. “The first one is proteins built from nitrogen. In developing countries this can be a big issue, because many diets in these countries aren’t rich in proteins and plants grown at elevated CO₂ can have twenty to thirty percent less protein. The second one is iron. Iron deficiency already affects an estimated 2 billion people worldwide.”

Beyond global food systems, the lowered mineral status of plants due to increased atmospheric CO₂ levels may lead to a negative feedback loop for mitigating climate change. “The terrestrial carbon sink associated with enhanced photosynthesis may be limited if most of the vegetation is deficient in nitrogen and other minerals, which may prevent any additional increase of CO₂ capture from the atmosphere,” says Gojon.

“We would like to really understand the mechanisms that are responsible for the negative effects of elevated CO₂ on the mineral composition of plants,” says Martin. “For example, we are currently exploring the natural genetic variation behind these negative effects, that could be used afterward to improve crops nutritional value under future CO₂ atmosphere.”

Reference: “The decline of plant mineral nutrition under rising CO₂: physiological and molecular aspects of a bad deal” by Alain Gojon, Océane Cassan, Liên Bach, Laurence Lejay and Antoine Martin, 3 November 2022, Trends in Plant Science.
DOI: 10.1016/j.tplants.2022.09.002

This work was supported by the I-Site MUSEThe Multi Unit Spectroscopic Explorer (MUSE) is a panoramic integral-field spectrograph on ESO's Very Large Telescope in Chile. It operates in the visible wavelength range and helps astronomers reveal objects that cannot be found in imaging surveys.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>MUSE, the CNRS through the MITI interdisciplinary PRIME program, and the BAP department of INRAE.