How does rising atmospheric CO2 affect marine organisms?

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Effects of Elevated CO2 on Regrowth of a Tropical Tree
Hoffmann, W.A., Bazzaz, F.A., Chatterton, N.J., Harrison, P.A. and Jackson, R.B.  2000.  Elevated CO2 enhances resprouting of a tropical savanna tree.  Oecologia 123: 312-317.

What was done
A tree common to the Brazilian savannah (Keilmeyera coriacea) was germinated and grown in controlled environmental chambers receiving combinations of ambient (350 ppm) and elevated (700 ppm) atmospheric CO2 concentrations and low- and high-strength soil nutrient solutions.  In addition, at 10 weeks post-germination, half of the seedlings in each treatment combination were clipped to the ground to simulate burning, thus allowing the authors to study the interactive effects of elevated CO2 and soil nutrients on seedling growth and regrowth with and without the presence of a simulated burning event.

What was learned
In uncut seedlings, atmospheric CO2 enrichment increased total dry weight by about 50%, while high nutrient solutions increased this parameter by 22%.  There were no significant interactions between elevated CO2 and nutrient status on growth in uncut seedlings.  However, in seedlings subjected to a simulated burning event, elevated CO2 had a significant impact on regrowth, but only in the presence of high soil nutrient availability, when it stimulated regrowth by nearly 300%!  This observation, coupled with the knowledge that large pulses of nutrients typically become available in soils following burning events, led the authors to conclude that "under elevated CO2, enhanced growth following fire will reduce the time required for individuals to regain the pre-burn size, minimizing the negative effect of fire on population growth."  Moreover, they state that "greater growth rates and higher capacities of regeneration under elevated CO2 are expected to increase the ability of woody plants to withstand the high fire frequencies currently prevalent in moist savannahs throughout the tropics."

What it means
As the air's CO2 content rises, unburned seedlings of Keilmeyera coriacea are likely to exhibit increased growth rates and biomass production, regardless of soil nutrient availability.  After burning events, which drastically reduce seedling biomass, it is likely that seedlings will exhibit even greater CO2-induced increases in rates of regrowth and production of new tissues.  Thus, the rising CO2 content of the atmosphere will help woody plant species recover from fires that frequent tropical savannahs.

Reviewed 25 October 2000