The identity of black alder (Alnus glutinosa (L.) Gaertn.) ectomycorrhizas was investigated using PCR/RFLP analysis of the ITS region from 16 morphotypes sampled at a 60-yr-old black alder stand. A comparison was made with restriction patterns from sporocarps of 28 mycobionts, of which 16 originated from the same stand, the remaining 12 came from two geographically distant alder stands. Eight of the mycorrhizal types could thus be identified, whereas eight mycorrhizal types remained unidentified. The identified mycorrhizas belonged to the genera Russula, Lactarius, Naucoria and Cortinarius. Four of the identified ectomycorrhizal types had identical PCR/RFLP profiles to corresponding fruit bodies from all investigated stands with no detectable intraspecific variation, despite the geographical distance of c. 300 km between the sampling locations. By contrast, intraspecific variation between sporocarps from the different locations was detected in Paxillus rubicundulus, mycorrhizas of which were not found. The diversity of fruiting alder mycobionts at the main experimental plot only partly matched the diversity observed from mycorrhizas when comparing their PCR/RFLP profiles. The results are discussed regarding sampling techniques, PCR/RFLP analyses and ecological aspects.

Leaves of two species, alder (Alnus glutinosa) and holm-oak (Quercus ilex), were exposed in bags of two mesh sizes in two climatically contrasting sites of a Corsican softwater stream. Leaves were incubated both in winter and in summer for about 6 months. The field experiment was designed to determine the influence of both spatial (climate) and temporal (season) variations of temperature, as well as differences in the chemical and physical properties of sclerophyllous and malacophyllous leaves, on leaf decomposition rates. Comparisons were made between leaves colonized by macroinvertebrates and leaves protected by finemesh. In winter and summer, holm-oak leaves were colonized much less by macroinvertebrates than alder leaves. Spatial and temporal differences in leaf litter processing were mainly dependent on three factors (i) the chemical and physical properties of the leaves, (ii) the abundance of macroinvertebrates in the sediment and (iii) the temperature. The climatical pattern of temperature had a greater influence than its seasonal pattern. In contrast with many other studies, abiotic factors dominated over biotic factors in this study.