Increasing carbon dioxide is making our food less nutritious

Elevated atmospheric carbon dioxide levels negatively impact key mineral nutrients in plants, reducing the nutrition derived from consuming them, reveals a recent review article in the Trends in Plant Science Journal which summarises findings from several studies. The review by scientists from France explained that almost all C3 plants – which employ the C3 pathway for photosynthesis where the first carbon compound has three carbon atoms – that are exposed to elevated levels of carbon dioxide show reduction across nutrients such as nitrogen, phosphorus, potassium, iron, zinc, magnesium and sulphur.

Estimates reveal that compared to the pre-industrial era, atmospheric carbon dioxide levels are now 50 percent higher. In 2022, global average carbon dioxide levels rose to 417.06 parts per million, resulting in a new record increase.

In May this year, carbon dioxide levels measured by NOAA’s Global Monitoring Laboratory averaged 424.0 parts per million (ppm), an increase of 3.0 ppm over May 2022.

While being a vital resource for plants, carbon dioxide is also among the prominent greenhouse gases. Considering that the majority of plants on the planet, including cereals like wheat, rice, barley and oats, use the C3 pathway, the review article raised alarm bells about increasing carbon dioxide levels not only impact the quantity of food produced but also its quality.

Although this phenomenon was recorded about two decades ago, recent evidence has aided in establishing the extent of its impact, states the review article.

Crops face the brunt of human actions from above and below

While the review article has resurfaced the conversation on climate change and its impact on the nutritional value of crops, from an Indian context, the topic gains significance given the country’s difficulties with meeting food and nutrition requirements. According to the Global Hunger Index (GHI) 2022, India ranked 107 out of 121 countries and has a hunger issue that has been designated as serious. GHI 2022 also stated that India has the highest child wasting rate (children who are too thin for their height) in the world. In 2022, a report published in the BMJ Global Health highlighted that severe acute malnutrition has drastically increased in India over the last two decades.

In light of these findings, the fact that crops are becoming inherently less nutritious is worrisome, said Dr. Hemapriya Natesan, Founder & CEO My Little Moppet, an e-commerce platform for children’s food products.

Dr. Natesan explained that early food choices are vital in establishing healthy eating patterns in the future, and optimal nutrition at the right time makes all the difference. While this may seem like a well-established fact, as a mother and a doctor, Dr. Natesan has both seen the impacts of inadequate nutrition and faced challenges in providing optimal nutrition in a landscape where sugar-laden cereals are the norm.

When you add the influence of rising carbon dioxide levels to the above scenario, it makes it more complicated.

While the nutritional challenges are one part of the issue, elevated carbon dioxide levels also alter the balance in the soil, making it difficult to implement sustainable agricultural practices, explained G. Ravikanth, Associate Professor in the Suri Sehgal Centre For Biodiversity And Conservation, Ashoka Trust for Research in Ecology and the Environment (ATREE), Bangalore.

“When plants are exposed to more carbon dioxide, there is increased photosynthesis, which in turn leads to more biomass. To meet the new demand, plants try to draw more nutrients from the soil. Additionally, the carbon dioxide also affects the soil’s microflora, thereby impacting the decomposition rates in the soil and influencing the nutrients available to plants,” he said. The vicious cycle makes it difficult to grow crops without the addition of external nutrients, he remarked.

Just like India’s troubled nutritional landscape, the Global Soil Biodiversity Atlas published in 2016 revealed that India’s soil organisms are at high risk due to various threats such as pollution, intensive agriculture, erosion and climate change, among others.

A separate research study published in 2018 revealed that elevated atmospheric carbon dioxide impacts not only micronutrients but also the protein and vitamin content of rice grains. The study found that apart from protein, zinc and iron, carbon dioxide levels also lead to a decline in B1, B2, B5 and B9 vitamins. While the exact health outcomes are difficult to measure, considering the fact that rice is the primary food source for more than half of the world’s population, these deficiencies can pose significant health risks.

Lewis H. Ziska, Associate Professor in the Environmental Health Sciences at the Mailman School of Public Health, Columbia University, who is one of the co-authors of the study, writes in a related blog post that these silent changes to plant physiology are often not part of mainstream narratives about the effects of rising carbon dioxide as they are hard to envisage. In an email interview, Ziska reiterated the importance of understanding these underlying changes. “The larger implications of reduced nutritional values are enormous, not only in terms of human health through CO₂-induced effects on protein, vitamins and micronutrients, but the role that this will also play in regards to the global food chain,” said Ziska, who has also written a book on the impact of carbon dioxide on plants and life.

Diversity in crops can help address nutrition 

Talking about a possible solution to the issue, Ravikanth of ATREE admitted that it is a complex problem to solve, but one way to prepare for a nutritionally challenged future is to grow plants that better assimilate nutrients from the soil and provide optimal yields. Trials are ongoing at various research centres such as the University of Agricultural Sciences, GKVK, Bengaluru.

Ziska added that at the policy-level, crop lines that have higher nutrient content must also be incentivised to encourage their cultivation.

“The earth provides a wide array of genetics among plants that we consume. Encouraging diversity in both time (crop rotation) and space (planting different crop lines in the same location) are absolutely essential in addressing the nutrition issue,” said Ziska.

Natesan further added that the approach is paramount not only on the field but also on the plate. “Climate change mitigation requires all stakeholders to work together and come up with long term solutions. But what we can do right now is focus on consuming more traditional grains and ensuring a healthier diet, free of chemical inputs, so we address these deficiencies early on to the best of our abilities,” she said.

CITATION:

Gojon A, Cassan O, Bach L, Lejay L, Martin A. The decline of plant mineral nutrition under rising CO2: physiological and molecular aspects of a bad deal. Trends Plant Sci. 2023 Feb;28(2):185-198. doi: 10.1016/j.tplants.2022.09.002. Epub 2022 Nov 3. PMID: 36336557.

Chunwu Zhu et al., Carbon dioxide (CO2) levels this century will alter the protein, micronutrients, and vitamin content of rice grains with potential health consequences for the poorest rice-dependent countries.Sci. Adv.4, 2018.

Banner image: A vendor selling vegetables in Howrah, West Bengal. Photo by Biswarup Ganguly/Wikimedia Commons.