Field decomposition of leaf litters: relationships between decomposition rates and soil moisture, soil temperature and earthworm activity

Abstract

The decomposition of leaf litter from four Mediterranean tree species (sessile oak, Quercus petraea L.; holm oak, Quercus ilex L.; sweet chestnut, Castanea sativa Mill and beech, Fagus sylvatica L.) was studied in litterbags for more than 2 y in an altitudinal transect from 380 to 860 m. The three experimental sites (Anduze, Le Vernet and Salidès) differed in their climatic conditions and in earthworm abundance (epigeous+anecics+epianecics=16, 17 and 181 g m −2 at the Salidès, Le Vernet and Anduze sites, respectively). After 2 y, Fagus sylvatica was the least decomposed litter whatever the site (38.5%±6.6 to 61.7%±8.0) followed by Q. ilex (62.7%±8.5 to 70.4%±5.7), Q. petraea (63.5%±8.6 to 84.6%±6.5) and C. sativa (65.8%±7.5 to 88.6%±5.7). During the first year (from 314 to 376 d depending on the litters) the effect of earthworms on litter decomposition was negligible at Anduze despite having the highest earthworm concentration. Thereafter, the litter decomposition rate was increased by a factor of from 3 to 10 depending on the litter. This pattern is explained by an enhanced litter palatability for earthworms after 1 y in the field and by litter consumption during the second year. At the Anduze site, litter decomposition was mostly controlled by earthworm activity. In contrast at the Le Vernet and Salidès sites which contained a much smaller earthworm community, climatic conditions (soil moisture and temperature) played the most important role in litter decomposition. A model relating climatic variables (soil moisture and temperature) to litter decomposition is described that allows a possible estimation (1) of the decomposition time for some Mediterranean litters, and (2) of the effects of microorganisms and earthworms on litter decay.