How does rising atmospheric CO2 affect marine organisms?

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Arbuscular Mycorrhizal Fungi: Do They Alter the Growth Response of Lolium perenne to Elevated CO2?
Hartwig, U.A., Wittmann, P., Braun, R., Hartwig-Raz, B., Jansa, J., Mozafar, A., Luscher, A., Leuann, A., Frossard, E. and Nosberger, J.  2002.  Arbuscular mycorrhiza infection enhances the growth response of Lolium perenne to elevated atmospheric pCO2Journal of Experimental Botany 53: 1207-1213.

What was done
Perennial ryegrass (Lolium perenne L.) was grown in environmental chambers receiving atmospheric CO2 concentrations of 350 and 600 ppm for 60 days.  In addition, plants were subjected to low and high levels of soil nitrogen and were inoculated with or without arbuscular mycorrhizal fungi.  Thus, the authors studied the interactive effects elevated CO2, soil nitrogen, and arbuscular mycorrhizal fungi on growth in this important grassland species.

What was learned
Elevated CO2 increased plant biomass by 10 and 17% at low and high levels of soil nitrogen, respectively.  However, when plants were inoculated with the arbuscular mycorrhizal fungi, elevated CO2 only enhanced plant biomass by 3% at low soil nitrogen, but it increased it by 41% at high soil nitrogen.  Thus, at high soil nitrogen, the presence of this symbiotic fungi more than doubled the plant growth response to atmospheric CO2 enrichment.  In addition, the amount of root colonization by the arbuscular mycorrhizal fungi increased by 56% in the high CO2 treatment.

What it means
As the air's CO2 content increases, it is likely that perennial ryegrass will respond by exhibiting enhanced biomass production, even in nitrogen-poor soils.  In addition, due to the positive CO2 x fungi interaction, plants growing in association with these symbionts will likely display even greater amounts of biomass production, especially if soil nutrients are plentiful.  Clearly, arbuscular mycorrhizal fungi play an important role in increasing the CO2-induced growth response of this grassland species; and they may well play a similar role with respect to entire grasslands.

Reviewed 3 July 2002