How does rising atmospheric CO2 affect marine organisms?

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Response of an Orchid to Super-Elevated CO2
Gouk, S.S., He, J. and Hew, C.S.  1999.  Changes in photosynthetic capability and carbohydrate production in an epiphytic CAM orchid plantlet exposed to super-elevated CO2Environmental and Experimental Botany 41: 219-230.

What was done
The authors grew an orchid plantlet, Mokara Yellow, in plastic bags flushed with 350 and 10,000 ppm CO2 for three months to study the effects of elevated CO2 on this epiphytic CAM species.

What was learned
Super-elevated CO2 enhanced total dry weight of plantlets by more than 2-fold, when compared to dry weights of plantlets grown at ambient CO2.  Interestingly, atmospheric CO2 enrichment not only significantly increased the growth of existing roots, it also increased the induction of new roots from internodes located on orchid stems.  Total chlorophyll content was increased by elevated CO2 in young leaves and roots by 64 and 118%, respectively, thus permitting greater light harvesting during the process of photosynthesis.  Greater utilization of sunlight in CO2-enriched plantlets likely contributed to tissue starch contents that were nearly 20-fold higher than those measured in control plantlets.  In spite of this large accumulation of starch, no disruption or damage of chloroplasts was evident in leaves and roots of CO2-enriched plantlets.

What it means
As the CO2 content of the air continues to rise higher and higher, it is likely that this CAM species will exhibit enhanced rates of photosynthesis and growth, leading to ever-increasing gains in biomass.  Roots, in particular, should increase their size more than leaves, thus acting as large sinks for leaf-derived carbohydrates, which may keep photosynthetic acclimation from occurring due to end product feedback inhibition.

Reviewed 1 August 1999