How does rising atmospheric CO2 affect marine organisms?

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Long-Term Effects of Elevated
CO2 on Arbutus unedo Trees

Bartak, M., Raschi, A. and Tognetti, R.  1999.  Photosynthetic characteristics of sun and shade leaves in the canopy of Arbutus unedo L. trees exposed to in situ long-term elevated CO2Photosynthetica 37: 1-16.

What was done
The authors studied the long-term effects of atmospheric CO2 enrichment on mature Arbutus unedo L. trees growing near CO2-emitting vents in central Italy.  At different distances from the CO2 vents, physiological measurements were made on trees that had been exposed to atmospheric CO2 concentrations of approximately 355 and 465 ppm throughout their entire 30-year lifetimes.

What was learned
The modest 30% increase in atmospheric CO2 boosted net photosynthetic rates in this perennial evergreen species by 110 to 140%, depending upon light intensity.  Moreover, there was no evidence of photosynthetic acclimation to elevated CO2.  Because stomatal conductance was similar in leaves of CO2-enriched and control trees, water-use efficiency in CO2-enriched leaves was more than 100% greater than that observed in leaves exposed to 355 ppm CO2.

What it means
As the atmospheric CO2 concentration rises, it is likely that this Mediterranean forest species will exhibit significant gains in photosynthesis and growth.  Moreover, this tree species should display significant improvements in its water-use efficiency, allowing it to better cope with periods of water stress, which commonly occur in its natural habitat.  It is likely that these enhancements in photosynthesis and growth will lead to greater carbon sequestration by this species, which should help reduce the rate of rise of atmospheric CO2.