FIELD DECOMPOSITION OF LEAF LITTERS - RELATIONSHIPS BETWEEN DECOMPOSITION RATES AND SOIL-MOISTURE, SOIL-TEMPERATURE AND EARTHWORM ACTIVITY

The decomposition of leaf litter from four Mediterranean tree species (sessile oak, Quercus petraea L.; helm oak, Quercus ilex L.; sweet che stnut, Castanea sativa Mill and beech, Fagus sylvatica L.) was studied in litterbags for more than 2y in an altitudinal transect from 380 to 860 m. The three experimental sites (Anduze, Le Vernet and Salides) d iffered in their climatic conditions and in earthworm abundance (epige ous + anecics + epianecics = 16, 17 and 181 g m(-2) at the Salides, Le Vernet and Anduze sites, respectively). After 2y, 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. pet raea (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 negl igible at Anduze despite having the highest earthworm concentration. T hereafter, 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 ly in the held and b y litter consumption during the second year. At the Anduze site, litte r decomposition Was mostly controlled by earthworm activity. In contra st at the Le Vernet and Salides sites which contained a much smaller e arthworm community, climatic conditions (soil moisture and temperature ) played the most important role in litter decomposition. A model rela ting climatic variables (soil moisture and temperature) to litter deco mposition is described that allows a possible estimation (1) of the de composition time for some Mediterranean litters, and (2) of the effect s of microorganisms and earthworms on litter decay. (C) 1998 Elsevier Science Ltd. All rights reserved.