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Effects of Elevated CO2 on Aspen Leaf Litter Quality and Decomposition
King, J.S., Pregitzer, K.S., Zak, D.R., Kubiske, M.E., Ashby, J.A. and Holmes, W.E.  2001.  Chemistry and decomposition of litter from Populus tremuloides Michaux grown at elevated atmospheric CO2 and varying N availability.  Global Change Biology 7: 65-74.

What was done
Aspen (Populus tremuloides) seedlings were grown for five months in
open-top chambers receiving atmospheric CO2 concentrations of 350 and 700 ppm.  At the end of this period, naturally senesced leaf litter was collected, analyzed, and allowed to decompose under ambient conditions for 111 days.  Thus, the authors studied the effects of elevated CO2 on aspen leaf litter quality and decomposition.

What was learned
Although elevated CO2 lowered leaf litter nitrogen content to 21 mg g-1 from the ambient living-leaf value of 23 mg g-1, it had no effect on litter sugar, starch or tannin concentrations.  Thus, with little to no CO2-induced effects on leaf litter quality of aspen seedlings, it was not surprising the authors found no CO2-induced effects on litter decomposition rates.

What it means
As the air's CO2 content increases, it is likely that few, if any, changes in green leaf chemistry will persist in naturally senesced leaf litter of aspen seedlings.  In addition, because leaf litter will likely be unaffected by increases in the air's CO2 concentration, its subsequent decomposition should similarly be unaffected.  In fact, the authors say they "found very minor changes in litter chemistry under elevated atmospheric CO2, and rates of decomposition were unaltered."  Thus, the rates of litter decomposition and nutrient cycling in aspen stands should change little with future increases in the air's CO2 concentration, so that more carbon should be sequestered in the soils on which they grow in a future high-CO2 world as a result of the greater litter production resulting from the aerial fertilization effect of atmospheric CO2 enrichment.