Ectomycorrhizal (ECM) communities were assessed on a 720 m(2) plot along a chronosequence of red oak (Quercus rubra) stands on a forest reclamation site with disturbed soil in the lignite mining area of Lower Lusatia (Brandenburg, Germany). Adjacent to the mining area, a red oak reference stand with undisturbed soil was investigated reflecting mycorrhiza diversity of the intact landscape. Aboveground, sporocarp surveys were carried out during the fruiting season in a 2-week interval in the years 2002 and 2003. Belowground, ECM morphotypes were identified by comparing sequences of the internal transcribed spacer regions from nuclear rDNA with sequences from the GenBank database. Fifteen ECM fungal species were identified as sporocarps and 61 belowground as determined by morphological/anatomical and molecular analysis of their ectomycorrhizas. The number of ECM morphotypes increased with stand age along the chronosequence. However, the number of morphotypes was lower in stands with disturbed soil than with undisturbed soil. All stands showed site-specific ECM communities with low similarity between the chronosequence stands. The dominant ECM species in nearly all stands was Cenococcum geophilum, which reached an abundance approaching 80% in the 21-year-old chronosequence stand. Colonization rate of red oak was high (>95%) at all stands besides the youngest chronosequence stand where colonization rate was only 15%. This supports our idea that artificial inoculation with site-adapted mycorrhizal fungi would enhance colonization rate of red oak and thus plant growth and survival in the first years after outplanting.

The occurrence and amount of soluble and insoluble phenolics in mycorrhizal and non-mycorrhizal roots of Picea abies (L.) Karst, were investigated, p-Hydroxybenzoic acid glucoside, picein, piceatannol and its glucoside, isorhapontin, catechin and ferulic acid could be identified by high-performance liquid chromatography in mycorrhizas of Picea abies-Lactarius deterrimus and Picea abies-Laccaria amethystea. Both types were collected from axenic cultures and the latter also from a spruce stand. The same phenolics occurred in non-mycorrhizal short roots from sterile cultures. However, the amounts of p-hydroxybenzoic acid glucoside, picein, catechin and cell wall-bound ferulic acid were considerably reduced in mycorrhizas from axenic culture, whereas the hydroxystilbenes piceatannol, its glucoside and worhapontin were not significantly reduced. Pure mycelia of Laccaria amethystea (Bull.) Murr, and Lactarius deterrimus Gröger were also analysed for phenolic compounds. Both fungal species contained none of the identified phenolics. The results are discussed with respect to mycorrhization in different mycorrhizal types.

Peroxidase (EC 1.11.1.7) and laccase (EC 1.10.3.1) activities were determined in mycorrhizal and non-mycorrhizal main and lateral roots of Picea abies (L.) Karst. (Norway spruce) and Larix decidua Mill, (larch) and in mycelia of the ectomycorrhizal fungus Laccaria amethystea (Bull.) Murr. grown under axenic conditions. Peroxidase isozyme patterns were identified after isoelectric focussing. In both tree species, mycorrhizae contained the lowest, and laterals of noninoculated plants the highest, peroxidase activities. Pure mycelia of Laccaria amethystea contained considerable laccase activity but no peroxidase activity. Laccase activity was barely detected in noninoculated laterals of spruce, but was present in noninoculated laterals of larch and in main roots of Norway spruce and larch. Highest laccase activities were found in mycorrhizae of both tree species, indicating that most of the activity was derived from the fungus. Laterals of Norway spruce contained eight, and those of larch five, acidic peroxidase isozymes. In mycorrhizae of Norway spruce and larch, specific peroxidase isozymes with pI values of 4.5 and 6.2 and 5.8 and 6.0, respectively, were almost completely suppressed. The specific suppression of peroxidase suggests that the fungal symbiont is able to modify the host defence response in mature mycorrhizae. Key words: defence mechanism, laccase, mycorrhiza, peroxidase (isozymes), plant–fungus interaction.

Relatively few ectomycorrhizal fungal species are known to form sclerotia. Usually, sclerotia are initiated at the extraradical mycelium. In this study, we present anatomical and ultrastructural evidence for the formation of sclerotia directly in the hyphal mantle of the mycorrhizal morphotype Pinirhiza sclerotia. A dark-pigmented fungal strain was isolated from Pinirhiza sclerotia and identified by molecular tools as Acephala macrosclerotiorum sp. nov., a close relative of Phialocephala fortinii s.l. As dark septate fungi are known to be mostly endophytic, resyntheses with Pinus sylvestris and A. macrosclerotiorum as well as Populus tremula x Populus tremuloides and A. macrosclerotiorum or P. fortinii s.l. were performed under axenic conditions. No mycorrhizas were found when hybrid aspen was inoculated with A. macrosclerotiorum or P. fortinii. However, A. macrosclerotiorum formed true ectomycorrhizas in vitro with P. sylvestris. Anatomical and ultrastructural features of this ectomycorrhiza are presented. The natural and synthesized ectomycorrhizal morphotypes were identical and characterized by a thin hyphal mantle that bore sclerotia in a later ontogenetic stage. The Hartig net was well-developed and grew up to the endodermis. To our knowledge, this is the first evidence at the anatomical and ultrastructural level that a close relative of P. fortinii s.l. forms true ectomycorrhizas with a coniferous host.

Soluble and cell-wall-bound phenolics in mycorrhizas of Larix decidua-Laccaria amethystea and in nonmycorrhizal fine roots of larch grown in sterile culture were analyzed by HPLC. The soluble phenolics p-hydroxybenzoylglucose, p-hydroxybenzoic acid glucoside, picein, catechin, and epicatechin were identified in nonmycorrhizal fine roots. The same phenolics also occurred in mycorrhizas, but only in very small quantities compared with those in nonmycorrhizal fine roots. The amount of cell-wall-bound ferulic acid was much lower in mycorrhizas than in nonmycorrhizal fine roots. Pure mycelia of Laccaria amethystea (Bull.) Murr. contained none of the identified phenolics. We conclude that L. amethystea induced a large decrease in soluble and cell-wall-bound phenolics in fine roots of Larix decidua Mill. that may explain their rapid mycorrhization.