Litter quality and decomposition in a CO2-enriched Mediterranean forest ecosystem

Six large open top chambers were installed to test the effect of atmospheri c [CO2] enrichment on clumps of natural Mediterranean vegetation starting f rom early spring 1992. To study the impact of [CO2] enrichment on litter de composition, leaves of three woody species (Quercus ilex L., Phillyrea angu stifolia L. and Pistacia lentiscus L.) were collected from the forest floor and subsequently incubated in situ over a two-year period. The initial slo pe of the exponential function, describing mass loss, indicated that there was a small negative effect of elevated [CO2] on the decomposition rate of all the species. All regressions were significant. The decrease of decompos ition rate is particularly notable during the initial stages of decompositi on, when the differences of quality parameters, lignin/N and C/N were large r. This study points out that a decrease of decomposition rate may occur un der elevated [CO2] conditions; if this effect is coupled to an increase of primary production, there will be a net rise of C-storage in the soils of f orest ecosystems. Forest soils may, therefore, represent a potentially incr easing sink for this excess carbon.