Carbon dioxide enrichment is a standard tool in modern greenhouse horticulture, widely used to boost yields and accelerate crop growth. New research from Leiden University shows, however, that rising CO₂ concentrations also directly affect the nutritional composition of food crops, an issue with growing relevance for controlled-environment agriculture.
Published in Global Change Biology, the study by Sterre F. ter Haar, Peter M. van Bodegom, and Laura Scherer is the largest meta-analysis to date on CO₂-driven changes in crop nutrient content. It compiles data from 109 peer-reviewed studies, covering 43 crops and more than 29,000 paired observations of edible plant parts.
From climate change to food quality
The research was driven by concerns about diet quality under climate change rather than greenhouse performance or crop flavour. "We were curious about the effect of climate change on our diets," says Sterre ter Haar, Lecturer and Doctoral Candidate at Leiden University. "Specifically, we were interested in the direct relationship between CO₂ rise and food quality."
While climate impacts on food systems are often discussed in terms of yield losses or supply disruptions, the Leiden team focused on a more direct mechanism: changes in plant stoichiometry. As atmospheric CO₂ rises, the balance of elements such as zinc, iron and nitrogen in crops shifts, affecting nutritional value even when yields increase.
A measurable decline in nutrients
To compare studies conducted at different CO₂ concentrations, the researchers standardised all data to a common baseline of 350 ppm CO₂ and an elevated level of 550 ppm: concentrations that are societally relevant within this century.
Across all crops and nutrients combined, the analysis shows an average decline of 3.2%. Zinc showed the strongest and most consistent reductions, followed by iron and protein (measured via nitrogen). In some cases, the declines were much larger, including a 37.5% reduction in zinc in chickpeas, although this crop is not typically grown in greenhouses.
"What emerges very clearly is that plants do not respond uniformly," Sterre explains. "Nutrient shifts and losses are crop- and cultivar-specific, and different elements behave very differently under elevated CO₂."
Implications for greenhouse production
Although most data came from field and FACE (free-air CO₂ enrichment) experiments, greenhouse and growth-chamber studies were included. On average, nutrient declines measured indoors were smaller than those observed outdoors, but the direction of change was consistent.
This directly intersects with commercial greenhouse practice, where CO₂ concentrations of 700–1,000 ppm are commonly used. "Our work suggests that elevated CO₂ levels can lead to decreasing crop nutrient density." At the same time, she stresses that CO₂ enrichment cannot be evaluated in isolation. "CO₂ enrichment in greenhouses can increase crop yields and thus food availability, which is important in a world where many people still face hunger."
Rather than recommending immediate changes to enrichment strategies, the researchers frame nutrient density as an additional consideration. "We hope to broaden the food security discussion to include nutrient security to help inform decision-making processes."
Yield versus nutrient density
A key technical issue for greenhouse horticulture is the potential trade-off between yield gains and nutrient concentration. Elevated CO₂ increases carbohydrate production, which can dilute mineral concentrations if uptake does not keep pace.
"Our analysis confirms that this effect goes beyond simple carbon dilution. Nutrient responses vary by element, tissue type and species. Reproductive tissues (fruits, grains and seeds) showed significant declines, making the findings particularly relevant for fruiting greenhouse crops such as tomatoes, cucumbers and peppers."
Cultivar selection may therefore become increasingly important. "Breeders should prioritise cultivars that retain nutrient density while still providing satisfactory yields," she notes. "In this way, both food sufficiency and nutrient sufficiency can be part of the decision-making process."
Knowledge gaps and next steps
The study did not assess interactions between elevated CO₂ and other greenhouse variables such as light intensity, fertilisation, irrigation, substrates or temperature control. "Investigating specific practices to counteract CO₂-driven nutrient loss was outside of our study's scope," she mentions, adding that available co-factor data were included in an open database for future research.
The analysis also detected increases in some non-essential and potentially harmful elements, including lead, although data remain limited. "Instead of only looking at desirable nutrients, we should expand our measurements to include a broader range of nutrients, including heavy metals. You don't know what you don't measure, and you can't respond to what you don't know."
The study highlights research needs around long-term nutrient responses under sustained high CO₂, cultivar performance at commercial scale, and strategies to balance yield and nutritional quality.
While the meta-analysis does not offer prescriptive solutions, it provides a robust quantitative baseline. CO₂ enrichment remains a powerful production tool, but the findings suggest that nutrient outcomes may deserve greater attention alongside yield metrics.
For more information:
University of Leiden
Sterre ter Haar, Lecturer and Doctoral Candidate
[email protected]
