Summary1. Plants possess numerous mechanisms to control infections by deleterious organisms. Unspecific resistance mechanisms may, however, also exert ecological costs when they have a negative effect on beneficial plant-microbe interactions. Such negative effects may even cross the border between a plant's aerial parts and its roots and then affect very central functions such as nutrient uptake and root resistance to micro-organisms. Whereas an impaired nodulation indeed appears common after resistance expression in the leaves, contradictory results have been published for the case of arbuscular mycorrhizal (AM) fungi. 2. We analysed the effect of induction of resistance mechanisms in foliar tissues on AM colonization in soybean plants, using acibenzolar-S-methyl (ASM) as chemical elicitor. By determining different physiological and biochemical parameters, we assessed whether the effects are related to the activation of the plant defence mechanisms or rather to the re-allocation of primary metabolites. 3. Colonization with AM fungi transiently decreased after pathogen resistance mechanisms were elicited in the aerial parts of the plant. The induction with ASM led to a significant, yet moderate, defence response in the roots, which was modulated in mycorrhizal plants. No allocation or fitness costs associated with the induction of resistance were detected in this study. 4. Synthesis. Our study confirms a transient negative impact of the elicitation of foliar defences on root-AM interactions. The results show that induced resistance to foliar pathogens can (i) move from the above-ground to the below-ground compartment and (ii) affect mutualistic micro-organisms as well as plant pathogens. We also conclude that (iii) the negative effect is likely linked to changes in the defence status of the plant rather than to changes in resource allocation patterns and (iv) the AM association can modulate the activation of the plant defence mechanisms and overcome such effects.

Two study plots, burned and control, were established in autumn 1998 in a Quercus ilex forest located in northern Spain, part of which had been affected by a low intensity fire in 1994. Soil samples for ectomycorrhizae (ECM) were taken over a 3-year period in each study plot in spring, summer, autumn and winter. ECM morphotypes were identified and the relative abundance of each morphotype in each soil sample calculated, along with species richness, Shannon diversity index and percentage of mycorrhization in each soil sample. The relative abundance of certain ECM morphotypes differed between burned and control plots, and the percentage of mycorrhizal tips was significantly lower in the burned than in the control plot. Nevertheless, there were no significant differences in the diversity, species richness or species composition of the ECM community in the burned and control plots. The dominant ECM morphotypes in both stands were Cenococcum geophilum and several thelephoroid fungi. Sphaerosporella brunnea and Pisolithus tinctorius thrived especially in the burned plot, whereas three ectomycorrhizal morphotypes assigned to the genus Hebeloma were especially abundant in the control plot. There was no significant variation in the relative abundance of the ECM morphotypes between seasons, but ECM community species richness was highest in autumn and lowest in summer. The percentage of mycorrhizal tips reached a maximum in winter, with its minimum in autumn. Collection of samples over the 3-year period also enabled us to detect a significant increase in percentage of ECM colonisation in the burned stand over time.

Fungi are a good source of digestible proteins and fibre, are low in fat and energy and make a useful contribution to vitamin and mineral intake. In terms of current dietary advice, 80 g fungi represent one portion of vegetables. Dried fungi and concentrated extracts are also used as medicines and dietary supplements. Some species show strong anti-tumour and antioxidant activity by enhancing various immune system functions and lowering cholesterol levels. Nevertheless, there are also some safety concerns. Edible species might be mistaken for poisonous ones, high heavy-metal concentrations in wild edible fungi (WEF) are a known source of chronic poisoning and the consumption of WEF can contribute markedly to the radiocaesium intake of human subjects. Some regions of Europe have a strong WEF tradition, especially eastern Europe. In the UK the consumption of wild fungi is considered of minor importance. Only one-third of adults consume fungi (cultivated species and WEF) throughout the UK; the average intake of fungi in the UK is estimated to be 0 . 12 kg fresh weight per capita per year. At least eighty-two species of wild fungi are recorded as being consumed in the UK, although certain species (e.g. chanterelle (Cantharellus cibarius), cep (Boletus edulis), oyster mushroom (Pleurotus ostreatus)) are favoured over others. Although WEF are not essential components in the daily diet, they are a nutritionally-valuable addition to the range of vegetables consumed, and their role in helping to avert food shortages in less-favoured areas should be definitely considered.

All available publications providing descriptions of ectomycorrhizas (ECM) were reviewed in order to build a database containing details on fungus forming the ECM, host tree, country where the material for description was collected, and habitat of the ECM. Other secondary data were also recorded. In all 1244 descriptions of ECM published since 1961 in 479 papers were reviewed. The number of different ECM morphotypes described was 814. Most ECM described were collected in Europe and North America. Gymnosperms were the most common tree associates, and boreal and temperate forests the most studied ecosystems. Fungal symbionts were mostly Basidiomycota, epigeous, and with mushroom-like morphology. The paper also addresses the gaps in ECM knowledge that mycorrhizologists should address in future studies.