Decomposition and nutrient dynamics of Quercus pubescens leaf litter in a naturally enriched CO2 Mediterranean ecosystem

摘要

The chemical composition (N, P, C, lignin and polyphenol concentrations) of Quercus pubescens leaf litter from mature trees growing close to a natural CO2 spring in Tuscany (Italy) was analysed, and compared to litter from a nearby reference site. Litter was incubated for 25 months at both the natural CO2 spring and the reference site, and monitored for decomposition rates, nutrient and lignin concentrations. Long-term exposure to elevated CO2 concentrations from the natural spring was associated with changes in the chemical composition of the oak leaf litter: decreases in P and polyphenol concentrations, and an increase in lignin. No differences in N concentrations were observed between the enriched CO2 litter from the natural spring and the reference litter. The decomposition rate was reduced in the CO2 spring leaf litter, with the lower P concentration of the native litter, combined with the lack of soil fauna observed at that site, being the factors most probably responsible for the measuredreductions in mass loss. However, litter from the CO2 spring and reference litter decomposed at the reference site showed similar rates of decomposition. All litter showed similar N concentrations during decomposition, with N being mineralized throughoutthe incubation period from both litter samples regardless of the site of incubation. In contrast, P dynamics differed between the two litters, with P being immobilized in the litter derived from the spring, and mineralized from the reference litter. When the litter from the spring was incubated at the reference site, there was a trend for net P uptake from the surrounding environment. The chemical composition of decomposing litter from the spring appeared to match that of the reference litter after 3 months of incubation at the reference site. The results from the CO2 spring suggest that litter decomposition may be retarded under elevated levels of atmospheric CO2. However, results from field surveys around CO2 vents should be viewed with caution because differences may relate to factors other than the known differences in CO2 concentrations.