How does rising atmospheric CO2 affect marine organisms?

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Effect of Elevated CO2 on Photosynthesis and Growth in a Sunfleck Light Regime
Leakey, A.D.B., Press, M.C., Scholes, J.D. and Watling, J.R.  2002.  Relative enhancement of photosynthesis and growth at elevated CO2 is greater under sunflecks than uniform irradiance in a tropical rain forest tree seedling.  Plant, Cell and Environment 25: 1701-1714.

What was done
The authors grew seedlings of Shorea leprosula (an under-story rain forest tree) in controlled environments maintained at atmospheric CO2 concentrations of 376 and 711 ppm in combination with low irradiance treatments delivered in a uniform or intermittent (sunfleck) manner for about seven months to study the effects of elevated CO2 and low light intensity on photosynthesis and growth in this species.

What was learned
Elevated CO2 increased light-saturated rates of photosynthesis by about 63%, regardless of light delivery treatment.  However, initial steady-state rates of photosynthesis measured in the shade in CO2-enriched leaves were approximately 109% greater than those observed in ambiently-grown leaves.  In addition, seedlings grown in elevated CO2 displayed post-irradiance rates of photosynthesis that were 14% greater than those observed in control seedlings.  Taken together, these increases in photosynthesis led to CO2-induced increases in carbon uptake that were 59 and 89% greater than those observed in control seedlings subjected to uniform and sunfleck light treatments, respectively.  Ultimately, seedlings subjected to uniform irradiance produced more biomass than seedlings exposed to sunfleck irradiance.  However, the CO2-induced percentage increase in biomass was greater under the sunfleck irradiance regime (60%) than under the uniform irradiance regime (25%).

What it means
As the air's CO2 content continues to rise, seedlings of Shorea leprosula growing in the understories of tropical rain forests will likely display increases in photosynthesis and biomass production.  Thus, this species will likely exhibit a greater capacity for carbon sequestration as the atmospheric CO2 concentration increases.

Reviewed 12 March 2003