How does rising atmospheric CO2 affect marine organisms?

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A Six-Year CO2 Enrichment Study of a Phosphorus-Poor and Water-Limited Grassland
Niklaus, P.A. and Korner, C.  2004.  Synthesis of a six-year study of calcareous grassland responses to in situ CO2 enrichment.  Ecological Monographs 74: 491-511.

What was done
The authors used screen-aided CO2 control (SACC) technology to enrich the air above a water-limited and phosphorus-poor temperate calcareous grassland in Switzerland with an extra 235 ppm of CO2 for a total of six years, over which period they measured a number of individual and community plant parameters.

What was learned
Peak percentage increases in biomass production in years 1 through 6 of the experiment were, respectively, 5%, 20%, 22%, 27%, 31% and 18%, for an average of 23.6% over the last five years of the study.  Year-to-year variability in this factor was best predicted by precipitation and resulting soil moisture differences, with the "obvious mechanism," in the words of the authors, being "soil moisture savings due to reduced stomatal conductance under elevated CO2," which would tend to "alleviate effects of water limitation more in dry years."

What it means
Although Niklaus and Korner note that "low available phosphorous ultimately limited community productivity and responses to CO2," this deficiency - coupled with a deficiency of water - was not sufficient to counter the growth-promoting effect of atmospheric CO2 enrichment, which in this particular case was equivalent to a 30% increase in growth in response to a standard 300-ppm increase in the air's CO2 concentration.

Reviewed 26 January 2005