How does rising atmospheric CO2 affect marine organisms?

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The Photosynthetic Response of the Common Cocklebur to Atmospheric CO2 Enrichment
Lewis, J.D., Wang, X.Z., Griffin, K.L. and Tissue, D.T.  2002.  Effects of age and ontogeny on photosynthetic responses of a determinate annual plant to elevated CO2 concentrations.  Plant, Cell and Environment 25: 359-368.

What was done
The authors grew the common cocklebur (Xanthium strumarium L.) in environmental chambers receiving atmospheric CO2 concentrations of 365 and 730 ppm for 70 days post-emergence to determine the effect of elevated CO2 on photosynthesis in this species over its developmental life cycle.

What was learned
As anticipated, elevated CO2 consistently boosted net photosynthetic rates in this species.  However, the magnitude of the response varied with plant development.  During the vegetative growth phase, for example, rates of photosynthesis in CO2-enriched plants were 30% greater than those exhibited by ambiently-grown plants.  In the flowering period, which ensued shortly thereafter, this stimulation was reduced to 10%, whereupon it increased to 20% during the fruiting period.

What it means
As the air's CO2 concentration increases, the common cocklebur will likely display enhanced rates of photosynthesis that should lead to greater biomass production.  More importantly, however, the data indicate that the CO2-responsiveness of a plant may depend upon its age and stage of development.

Reviewed 15 May 2002