How does rising atmospheric CO2 affect marine organisms?

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Photosynthetic Acclimation: Is It Affected by Light Availability?
Kubiske, M.E., Zak, D.R., Pregitzer, K.S. and Takeuchi, Y.  2002.  Photosynthetic acclimation of overstory Populus tremuloides and understory Acer saccharum to elevated atmospheric CO2 concentration: interactions with shade and soil nitrogen.  Tree Physiology 22: 321-329.

What was done
The authors grew aspen (Populus tremuloides) and sugar maple (Acer saccharum) seedlings for three years in open-top chambers receiving atmospheric CO2 concentrations of 360 and 560 ppm and low or high levels of soil nitrogen.  In addition, seedlings were grown with or without shade.  Thus, the authors studied the interactive effects of elevated CO2, soil nutrition, and shading on photosynthetic acclimation in these shade-intolerant (aspen) and shade-tolerant (sugar maple) trees.

What was learned
Photosynthetic acclimation occurred in both tree species, as indicated by CO2-induced reductions in their maximum rates of rubisco activity.  In addition, these responses were typically greater in shade leaves (vs. sun leaves) of shade-intolerant aspen seedlings and in sun leaves (vs. shade leaves) of shade-tolerant sugar maple.

What it means
As the air's CO2 content increases, aspen and sugar maple seedlings will likely respond by displaying increased rates of photosynthesis, in spite of photosynthetic acclimation that may be induced in these species.  In addition, since the fraction of sunlit leaves in under-story sugar maple trees is likely to be far less than the fraction of shaded leaves in upper-story aspen trees, there should be a greater acclimation of the totality of leaves of upper-story aspen trees than of the totality of leaves of under-story sugar maple trees, which suggests that shade-tolerant trees may well be more responsive to atmospheric CO2 enrichment than are shade-intolerant trees, as has indeed been observed in many instances (Kerstiens, 1998).

Kerstiens, G.  1998.  Shade-tolerance as a predictor of responses to elevated CO2 in trees.  Physiologia Plantarum 102: 472-480.

Reviewed 18 September 2002