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Effects of Elevated CO2 on the Decomposition of Litter from Ash and Sycamore Trees
Cotrufo, M.F., Briones, M.J.I. and Ineson, P.  1998.  Elevated CO2 affects field decomposition rate and palatability of tree leaf litter: importance of changes in substrate quality.  Soil Biology and Biochemistry 30: 1565-1571.

What was done
The authors grew two-year-old ash (Fraxinus excelsior L.) and sycamore (Acer pseudoplatanus L.) seedlings for one growing season in closed-top chambers (solar domes) receiving atmospheric CO2 concentrations of 350 and 600 ppm to study the effects of elevated CO2 on leaf tissue properties in these species.  In addition, biolitter samples from each species grown at each CO2 concentration were incubated in litter bags placed within a forest soil for one year to study the effects of growth CO2 concentration on subsequent litter decomposition rates.  Finally, leaves were fed to woodlouse arthropods (Oniscus asellus) to determine if elevated CO2 impacted their rates of foliage consumption.

What was learned
Elevated CO2 reduced nitrogen concentrations, but increased lignin contents, in biolitter produced from both tree species.  These changes in biolitter properties likely contributed to the decreased decomposition rates observed in CO2-enriched biolitter as compared to biolitter produced under ambient concentrations of CO2.  Indeed, after one-year of incubation, biolitter bags from CO2-enrihced trees - regardless of species - had about 30% more dry mass remaining in them than biolitter bags from ambient trees.  Finally, the woodlouse arthropods consumed 16% less biolitter generated from seedlings grown at 600 ppm CO2 than from biolitter generated from ambiently-grown seedlings.

What it means
As the CO2 content of the air increases, ash and sycamore seedlings will likely respond by increasing their rates of photosynthesis and biomass production.  These species should thus increase the amounts of biolitter they contribute to soils.  Moreover, due to CO2-induced changes in biolitter nitrogen and lignin contents, the rates of decomposition of the biolitter produced by the two species will likely be reduced.  In addition, biolitter consumption by the woodlouse arthropod will likely be reduced as well.  When all is said and done, therefore, these phenomena should enhance carbon sequestration within ecosystems dominated by ash and sycamore trees and perhaps other related species.

Reviewed 21 August 2002