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How will the ongoing rise in the air’s CO2 content alter the amounts of various health-promoting substances found in the plants that we commonly eat? Studies of the effects of atmospheric CO2 enrichment on the quality of the different plants that comprise our diets have typically lagged far behind studies designed to assess the effects of elevated CO2 on the quantity of plant production. Some noteworthy exceptions were the early studies of Barbale (1970) and Madsen (1971, 1975), who discovered that increasing the air’s CO2 content produced a modest increase in the vitamin C concentration of tomatoes, while Kimball and Mitchell (1981) demonstrated that enriching the air with CO2 also stimulated the tomato plant’s production of vitamin A. Then, a few years later, Tajiri (1985) found that a mere one-hour-per-day doubling of the air’s CO2 concentration actually doubled the vitamin C contents of bean sprouts, and that it did so over a period of only seven days.