Several studies have recently documented the effects of elevated atmospheric CO2 concentrations on photosynthesis in various fruiting trees. In an eight-day experiment, Pan et al. (1998) found that twice-ambient CO2 concentrations increased rates of net photosynthesis in one-year-old apple seedlings by 90%. In a longer three-month study, Keutgen and Chen (2001) noted that cuttings of Citrus madurensis exposed to 600 ppm CO2 displayed rates of photosynthesis that were more than 300% greater than rates observed in control cuttings exposed to 300 ppm CO2. Likewise, in the review paper of Schaffer et al. (1997), it was noted that atmospheric CO2 enrichment had previously been shown to enhance rates of net photosynthesis in various tropical and sub-tropical fruit trees, including avocado, banana, citrus, mango and mangosteen. Finally in the two-year study of Centritto et al. (1999a), cherry seedlings grown at 700 ppm CO2 exhibited photosynthetic rates that were 44% greater than those displayed by seedlings grown in ambient air, independent of a concomitant soil moisture treatment.
Because elevated CO2 enhances the photosynthetic rates of fruiting trees, it should also lead to increased biomass production in them. And it does. In the two-year study of Centritto et al. (1999b), for example, well-watered and water-stressed seedlings growing at twice-ambient CO2 concentrations displayed basal trunk areas that were 47 and 51% larger than their respective ambient controls. Similarly, in a study spanning more than thirteen years, Idso and Kimball (2001) demonstrated that the aboveground wood biomass of mature sour orange trees growing in air enriched with an additional 300 ppm of CO2 was 80% greater than that attained by control trees growing in ambient air.
In summary, as the CO2 content of the air increases, fruit trees will likely display enhanced rates of photosynthesis and biomass production, regardless of soil moisture conditions. Consequently, greater amounts of carbon will likely be sequestered in the woody trunks and branches of such species. Moreover, fruit yields may increase as well. In the study of Idso and Kimball, for example, they were stimulated to essentially the same degree as aboveground wood biomass, i.e., by 80% in response to a 75% increase in the air's CO2 content.
For more information on fruit-bearing tree growth responses to atmospheric CO2 enrichment see Plant Growth Data: Black Cherry (dry weight, photosynthesis), Calamondin (photosynthesis), Mango (dry weight), Marsh Grapefruit (photosynthesis, photosynthesis), Sour Orange (photosynthesis), Sweet Cherry (dry weight), Valencia Orange (photosynthesis, photosynthesis), and Washington Naval Orange (photosynthesis, photosynthesis).
References
Centritto, M., Magnani, F., Lee, H.S.J. and Jarvis, P.G. 1999a. Interactive effects of elevated [CO2] and drought on cherry (Prunus avium) seedlings. II. Photosynthetic capacity and water relations. New Phytologist 141: 141-153.
Centritto, M., Lee, H.S.J. and Jarvis, P.G. 1999b. Interactive effects of elevated [CO2] and drought on cherry (Prunus avium) seedlings. I. Growth, whole-plant water use efficiency and water loss. New Phytologist 141: 129-140.
Idso, S.B. and Kimball, B.A. 2001. CO2 enrichment of sour orange trees: 13 years and counting. Environmental and Experimental Botany 46: 147-153.
Keutgen, N. and Chen, K. 2001. Responses of citrus leaf photosynthesis, chlorophyll fluorescence, macronutrient and carbohydrate contents to elevated CO2. Journal of Plant Physiology 158: 1307-1316.
Pan, Q., Wang, Z. and Quebedeaux, B. 1998. Responses of the apple plant to CO2 enrichment: changes in photosynthesis, sorbitol, other soluble sugars, and starch. Australian Journal of Plant Physiology 25: 293-297.
Schaffer, B., Whiley, A.W., Searle, C. and Nissen, R.J. 1997. Leaf gas exchange, dry matter partitioning, and mineral element concentrations in mango as influenced by elevated atmospheric carbon dioxide and root restriction. Journal of the American Society of Horticultural Science 122: 849-855.