How does rising atmospheric CO2 affect marine organisms?

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Elevated CO2 and Crop Residue Decomposition
Torbert, H.A., Prior, S.A., Rogers, H.H. and Runion, G.B.  1998.  Crop residue decomposition as affected by growth under elevated atmospheric CO2Soil Science 163: 412-419.

What was done
Crop residues from soybean and grain sorghum plants grown at ambient and twice-ambient atmospheric CO2 concentrations were added to soil plots exposed to normal air to see if their decomposition rates were affected by their prior CO2 growth concentrations.  For both species, some plots received equal amounts of crop residue, regardless of CO2 growth concentration, while others received greater amounts of residue that reflected observed CO2-induced biomass increases.  Measurements of carbon evolution from the soil were gathered 3, 14, 30 and 60 days after residue addition to indirectly determine how much carbon remained in the soil.

What was learned
At all measurement times, with the exception of day 3, significantly lower amounts of carbon were lost from soils that were equally amended with crop residues grown in elevated CO2.  And soils amended with the weighted residues produced in elevated CO2, always exhibited significantly less carbon evolution.  In fact, after 60 days, the cumulative amount of carbon evolved from this treatment was about 40% less than that evolved from plots containing ambiently-produced crop residues.

What it means
As the CO2 content of the air rises ever higher, most plants will increase their photosynthetic rates, thereby removing more carbon from the atmosphere and integrating it into their tissues, which generally increases their carbon to nitrogen ratios.  Following senescence, leaves and stems typically fall to the ground and become incorporated into the soil, where the mineralization of their various elements occurs.  With higher carbon to nitrogen ratios, however, the amount of carbon mineralization may decrease as the air's CO2 concentration increases, thereby locking up greater stores of carbon in the soil and helping to slow the rate of rise of the air's CO2 content.

Reviewed 15 April 1999