Rising atmospheric CO2 levels pose many challenges to global climate, thus to all forms of life including plants. The impact of elevated CO2 on plant growth and development and the nutritional quality in relation to major nutrients in many crops has been explored extensively. However, information on the elevated CO2 effects on the health-promoting phytochemicals in food crops is rather limited. Major nutrients in food crops including protein, phosphorus, potassium, calcium, iron, zinc and other micronutrients in many food crops are known to be suppressed at elevated CO2 levels. Elevated CO2 increases carbohydrate accumulation but decreases nitrogen accumulation in plants thus affecting their C-N ratio. A number of studies show that high C-N ratio and nitrogen limiting conditions in plants can result in the accumulation of carbon-based secondary metabolites, many of which are health-promoting phytochemicals and allelochemicals involved in plants’ defense against pathogens and herbivory. Although the results from these studies are variable, it can be concluded that while elevated CO2 is known to suppress the content of major nutrients, it may actually have a favorable impact on the accumulation of carbon-based phytochemicals in food crops.
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