How does rising atmospheric CO2 affect marine organisms?

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CO2 and N2O Fluxes to and from Timothy-Sown Mesocosms
Kettunen, R., Saarnio, S. and Silvola, J. 2007. N2O fluxes and CO2 exchange at different N doses under elevated CO2 concentration in boreal agricultural mineral soil under Phleum pratense. Nutrient Cycling in Agroecosystems 78: 197-209.

Three of the important questions surrounding the environmental impact of the ongoing rise in the air's CO2 content concern its effects on the evolution of the greenhouse gas nitrous oxide or N2O from agricultural soils, the productivity of crops, and the potential for carbon storage in the soils upon which crops grow.

What was done
The authors grew timothy (Phleum pratense) from seed in sandy-soil-filled mesocosms located within greenhouses maintained at atmospheric CO2 concentrations of either 360 or 720 ppm for a period of 3.5 months at moderate (standard), low (half-standard) and high (1.5 times standard) soil nitrogen (N) supply, while they measured the evolution of N2O from the mesocosms, vegetative net CO2 exchange, and final above- and below-ground biomass production over the course of three harvests.

What was learned
The elevated CO2 concentration increased the net CO2 exchange of the ecosystems (which phenomenon was primarily driven by CO2-induced increases in photosynthesis) by about 30%, 46% and 34% at the low, moderate and high soil N levels, respectively, while it increased the above-ground biomass of the timothy crop by about 8%, 14% and 8% at the low, moderate and high soil N levels, and the below-ground biomass of the crop by 28%, 27% and 41% at the same respective soil N levels. In addition, Kettunen et al. report that "an explicit increase in N2O fluxes due to the elevated atmospheric CO2 concentration was not found."

What it means
All of the above findings are of a positive nature. Crop growth was enhanced by the experimental doubling of the air's CO2 content. There was no increase in the evolution of the greenhouse gas N2O from the soil. And the three Finnish researchers concluded that the high increase in the below-ground biomass indicates "enhanced photosynthate accumulation in the soil as a response to the increased CO2 concentration."

Reviewed 24 October 2007