How does rising atmospheric CO2 affect marine organisms?

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Prairie Community Response to Atmospheric CO2 Enrichment
Johnson, N.C., Wolf, J. and Koch, G.W.  2003.  Interactions among mycorrhizae, atmospheric CO2 and soil N impact plant community composition.  Ecology Letters 6: 532-540.

What was done
The authors grew communities of 14 common prairie plants in twelve greenhouse chambers at Flagstaff, Arizona, USA, six of which chambers were maintained at an atmospheric CO2 concentration of 450 ppm and six of which were maintained at 688 ppm during daylight hours (equivalent to 368 and 560 ppm at sea level, respectively).  Each of the CO2 treatments also had treatments of living or dead arbuscular mycorrhizal (AM) fungal inoculum and low or enriched soil nitrogen (N) content.

What was learned
After one growing season, it was determined, in the words of the authors, that "plant species richness was highest in mesocosms with elevated CO2, +AM fungi, and low soil N."  They also concluded that "in some plant species elevated CO2 can increase the net benefits of mycorrhizae by reducing their relative carbon cost."  Hence, not only did the extra CO2 directly help the various plant species in this experiment, it also helped them indirectly by promoting the growth of AM fungi, which provided additional benefits to the plants.

What it means
As the air's CO2 content continues to rise, it should have a tendency to maintain, and possibly even increase, the species richness of prairie ecosystems, especially where soil nitrogen content is less than optimal.

Reviewed 6 August 2003