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Effects of Elevated CO2 and O3 on Pine Needle Litter Decomposition
Kainulainen, P., Holopainen, T. and Holopainen, J.K.  2003.  Decomposition of secondary compounds from needle litter of Scots pine grown under elevated CO2 and O3Global Change Biology 9: 295-304.

What was done
The authors collected needle litter beneath 22-year-old Scots pine (Pinus sylvestris L.) trees that had been growing in open-top chambers for three years at atmospheric CO2 concentrations of 350 and 600 ppm in combination with ambient and elevated (approximately 1.4 x ambient) ozone concentrations to determine the impacts of these variables on the subsequent decomposition of senesced needles.  Needles were collected and placed in litterbags located within a native litter layer in a Scots pine forest.  Decomposition rates were assessed by measuring accumulated mass loss in needles over a period of 19 months.

What was learned
Simply stated, exposure to elevated CO2 during growth did not affect subsequent rates of decomposition of Scots pine needles, nor did elevated O3 exposure nor any combination of the two gases.

What it means
As the composition of trace gases in earth's atmosphere changes, particularly with respect to increasing CO2 and O3 concentrations, it would appear that the decomposition of needle litter in Scots pine forests will not be affected.  To be more confident of this conclusion, however, it would be good to conduct an experiment similar to this one with needle litter maintained in both ambient air and CO2- and O3-enriched air, since the latter situation recreates potential future atmospheric conditions with greater fidelity.

Reviewed 14 May 2003