How does rising atmospheric CO2 affect marine organisms?

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Trees Can Positively Respond to Elevated Levels of Atmospheric CO2 at Very Low Levels of Sunlight
Hattenschwiler, S.  2001.  Tree seedling growth in natural deep shade: functional traits related to interspecific variation in response to elevated CO2Oecologia 129: 31-42.

What was done
Seedlings of five temperate forest species (Fagus sylvatica, Acer pseudoplatanus, Quercus robur, Taxus baccata, and Abies alba) were grown in open-top chambers receiving atmospheric CO2 concentrations of 360, 500 and 660 ppm for two growing seasons.  They were also exposed to reduced light intensities of only 3.4 and 1.3% of full sunlight.  Thus, the author studied the interactive effects of elevated CO2 and low light intensities on the growth of these five tree species.

What was learned
When the seedlings were grown at 3.4% of full sunlight, all five species exhibited significant CO2-induced increases in total biomass.  At 660 ppm CO2, for example, the CO2-induced total biomass increases recorded for Fagus, Taxus, Acer, Quercus and Abies were 17, 16, 50, 31 and 62%, respectively.  At the lowest light intensity, which was only 1.3% of full sunlight, elevated CO2 continued to significantly increase the total biomass of the Fagus and Taxus seedlings.  The Fagus seedlings exhibited a 74% increase in total biomass when grown at either 500 or 660 ppm CO2, while the Taxus seedlings displayed 34 and 41% biomass increases at 500 and 660 ppm CO2, respectively.

What it means
As the CO2 content of the air increases, seedlings of these five temperate forest species will likely respond by increasing their photosynthetic rates and biomass production, even at very low intensities of sunlight.  Thus, the germination, recruitment and survival of these species on forest floors beneath closed canopies is likely to increase with increasing atmospheric CO2 concentration.

Reviewed 27 February 2002