How does rising atmospheric CO2 affect marine organisms?

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Response of Mango Trees to Elevated CO2
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.

What was done
Two mango ecotypes, one evolving from a warm, humid tropical climate, and the other from a cool, dry subtropical region, were grown for 12 months in glasshouses receiving 350 and 700 ppm CO2 to determine the effects of atmospheric CO2 enrichment on their growth and leaf mineral nutrient concentrations.

What was learned
Although atmospheric CO2 enrichment led to partial photosynthetic acclimation in both ecotypes, greater net carbon gains were still achieved with elevated CO2, as indicated by greater plant dry mass values for trees grown at 700 ppm CO2.  In both mango cultivars, elevated CO2 tended to decrease foliar concentrations of mineral nutrients (N, P, K, Ca, Mg, S, Cl, Fe, Zn, Mn, Cu and B), most likely due to a dilution effect, since atmospheric CO2 enrichment increased leaf dry mass.

What it means
As the CO2 content of the air rises, it is likely that mango biodiversity will be maintained, as there were no obvious differences in the responses of these two ecotypes to atmospheric CO2 enrichment.  In addition, these cultivars will likely increase their overall size, biomass, and yield as more and more CO2 enters the air from mankind's activities.  Although the instantaneous doubling of the atmospheric CO2 content in this experiment reduced concentrations of leaf mineral elements, the authors stated that "given the slow rate at which global atmospheric CO2 concentration is increasing, it is possible that plants will adapt to elevated ambient CO2 concentrations over time with respect to mineral nutrition," as did sour orange trees after 85 months of exposure to elevated CO2 (Penuelas et al., 1997).

Penuelas, J., Idso, S.B., Ribas, A. and Kimball, B.A.  1997.  Effects of long-term atmospheric CO2 enrichment on the mineral concentration of Citrus aurantium leaves.  New Phytologist 135: 439-444.

Reviewed 1 September 1999