How does rising atmospheric CO2 affect marine organisms?

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Citrus Trees - Summary
How does atmospheric CO2 enrichment affect the growth and development of citrus trees and the fruit they produce?

In the study of Keutgen and Chen (2001), cuttings of Citrus madurensis grown for three months at 600 ppm CO2 displayed rates of photosynthesis that were more than 300% greater than those measured on control cuttings grown at 300 ppm CO2.  In addition, elevated CO2 concentrations have been shown to increase photosynthetic rates in mango (Schaffer et al., 1997), mangosteen (Schaffer et al., 1999) and sweet orange (Jifon et al., 2002).  In the study of Jifon et al., it was further reported that twice-ambient CO2 concentrations increased photosynthetic rates in mycorrhizal- and non-mycorrhizal-treated sour orange seedlings by 118 and 18%, respectively.

Such CO2-induced increases in photosynthesis should ultimately lead to enhanced biomass production; and so they do.  Idso and Kimball (2001), for example, have documented how a 75% increase in the air's CO2 content has boosted the long-term production of aboveground wood and fruit biomass in sour orange trees by 80% in a study that has been ongoing since November of 1987.  Furthermore, Idso et al. (2002) have additionally demonstrated that the 300-ppm increase in the air's CO2 content has increased the fresh weight of individual oranges by an average of 4% and the vitamin C content of their juice by an average of 5%.

In summary, these peer-reviewed studies suggest that as the air's CO2 content slowly but steadily rises, citrus trees will respond by increasing their rates of photosynthesis and biomass production.  In addition, they may also increase the vitamin C content of their fruit, which may help to prevent an array of human health problems brought about by insufficient intake of vitamin C.

References
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.

Idso, S.B., Kimball, B.A., Shaw, P.E., Widmer, W., Vanderslice, J.T., Higgs, D.J., Montanari, A. and Clark, W.D.  2002.  The effect of elevated atmospheric CO2 on the vitamin C concentration of (sour) orange juice.  Agriculture, Ecosystems and Environment 90: 1-7.

Jifon, J.L., Graham, J.H., Drouillard, D.L. and Syvertsen, J.P.  2002.  Growth depression of mycorrhizal Citrus seedlings grown at high phosphorus supply is mitigated by elevated CO2New Phytologist 153: 133-142.

Keutgen, N. and Chen, K.  2001.  Responses of citrus leaf photosynthesis, chlorophyll fluorescence, macronutrient and carbohydrate contents to elevated CO2Journal of Plant Physiology 158: 1307-1316.

Schaffer, B., Whiley, A.W. and Searle, C.  1999.  Atmospheric CO2 enrichment, root restriction, photosynthesis, and dry-matter partitioning in subtropical and tropical fruit crops.  HortScience 34: 1033-1037.

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.