How does rising atmospheric CO2 affect marine organisms?

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Growth and N-Fixation Responses of Four Legumes to Atmospheric CO2 and Soil Nitrogen Additions
West, J.B., HilleRisLambers, J., Lee, T.D., Hobbie, S.E. and Reich, P.B.  2005.  Legume species identity and soil nitrogen supply determine symbiotic nitrogen-fixation responses to elevated atmospheric [CO2].  New Phytologist 167: 523-530.

What was done
In conjunction with the BioCON FACE experiment at the Cedar Creek Natural History Area in east central Minnesota, USA, the authors studied the growth and nitrogen fixation responses of four leguminous plants grown in monoculture - Amorpha canescens Pursh, Lespedeza capitata Mich., Lupinus perennis L., and Petalostemum villosum Nutt. - to an extra 192 ppm of atmospheric CO2 and an extra 4 g of soil nitrogen (N, in the form of NH4NO3) per m2 per year.

What was learned
With respect to the proportion of N derived from the atmosphere (Ndfa), the authors say that "within the ambient N treatment, Amorpha and Lespedeza showed increases in Ndfa with elevated CO2, whereas Lupinus and Petalostemum showed decreases."  Within the elevated N treatment, on the other hand, they report that "Amorpha Ndfa decreased with increased CO2 ... and the other three species exhibited little or no response to elevated CO2."

With respect to growth, aboveground biomass production in the ambient N treatment exhibited a hodgepodge of responses to elevated CO2, decreasing by about 30% in Amorpha, showing no effect in Petalostemum, rising by some 15% in Lupinus and skyrocketing by 250% in Lespedeza.  Within the elevated N treatment all responses were positive, with modest increases in Lupinus and Petalostemum (12 and 23%, respectively), a large increase in Amorpha (125%), and a monstrous increase in Lespedeza (420%).

What it means
West et al. conclude that "legume species identity and N supply are critical factors in determining symbiotic N-fixation responses to increased atmospheric CO2," and that "species identity may be an important factor controlling the response of N fixation to global change."  In terms of all-important growth, there also appears to be a wide range of responses among species; but it is encouraging to see that in the face of soil nitrogen additions, such as are likely to occur from continued atmospheric N deposition, the four leguminous plants of this study all exhibited increases in biomass production in response to atmospheric CO2 enrichment, with some of them being extremely large.

Reviewed 14 September 2005