Increasing levels of carbon dioxide (CO₂) in the environment may increase agricultural production at the expense of crop quality, according to a new analysis.

Leanne Jablonski and her colleagues at Ohio State University and Indiana University-Purdue University say that their analysis represents the first comprehensive and statistically robust summary of plant reproduction in environments with enriched CO₂. While the studies show that increased CO₂ concentrations markedly enhance fruit, flower, and seed production in domesticated crops, elevated CO₂ also appears to decrease the concentration of nitrogen in the seeds of both domesticated and wild plant species.

On average, the nitrogen concentration dropped by 14% in the seeds of 79 species for which data are available on growth changes in environments with enhanced CO₂. While both soybeans and rice were exceptions to this general trend, the effect was particularly pronounced on wheat seeds, which lost approximately 20% of their nitrogen concentrations. This means that people and animals would need to eat more of the crops with the reduced nitrogen content to get the same nutrition.

The researchers conclude that the trade-offs between quantity and quality need to be considered when the effects of rising CO₂ levels on agriculture are calculated. The ecological consequences of reduced nitrogen concentrations in seeds could be extensive, they claim. Because the populations of pollinators, as well as creatures whose diets are dependent upon consuming fruit and insects, could be altered, ecosystem functioning ultimately could be impacted. (New Phytologist 2002, 156, 9-26).