The effect of elevated atmospheric CO2 on the vitamin C concentration of (sour) orange juice

Well-watered and fertilized sour orange trees (Citrus aurantium L.) have been grown since the seedling stage (November 1987) out-of-doors at Phoenix, AZ, USA in clear-plastic-wall open-top chambers maintained at atmospheric CO2 concentrations of 400 and 700 mul/l. Over the 12-year period 1988-1999, all fruit produced by each tree were counted and weighed; and over the last 8 years of this period (1992-1999), the concentration of vitamin C in the juice of the fruit was measured. Based upon these data, it has. been determined that when the 75% increase in the air's CO2 concentration doubles fruit production, it increases the vitamin C concentration of the juice of the fruit by 7%. This nutritional enhancement is even greater in years when fruit production is more than doubled, due to the CO2-enriched fruit being slightly smaller than the ambient-treatment fruit in such circumstances, which increases the vitamin C concentration of the juice of the CO2-enriched fruit. In years when the CO2-induced increase in fruit production is less than 100%, however, the CO2-enriched fruit are generally slightly larger than the ambient-treatment fruit, which reduces the CO2-induced increase in juice vitamin C concentration below the basic 7% level characteristic of fruit of identical size. In what appears to be an approach to long-term equilibrium conditions, five of the last 6 years have seen the CO2-induced increase in the number of fruit produced hover at 74 +/- 9%, while the CO2-induced increase in fruit fresh weight has averaged 4 +/- 2% and the CO2-induced increase injuice vitamin C concentration has averaged 51%. Published by Elsevier Science B.V.