Summary• In order to clarify the functional role of individual ectomycorrhizal (EcM) fungal species in the field, we need to relate their abundance and distribution as mycorrhizas to their abundance and distribution as extramatrical mycelium (EMM).• We divided each of four 20 cm × 20 cm × 2 cm slices of pine forest soil into 100 cubes of 2 cm × 2 cm. For each cube, ectomycorrhizas were identified and the presence of EMM of the EcM fungi recorded as ectomycorrhizas was determined by terminal restriction fragment length polymorphism (T-RFLP) analysis of ITS rDNA.• Ectomycorrhizas and EMM of seven EcM species were mapped. Spatial segregation of mycorrhizas and EMM was evident and some species produced their EMM in different soil layers from their mycorrhizas.• The spatial relationship between mycorrhizas and their EMM generally conformed to their reported exploration types, but EMM of smooth types (e.g. Lactarius rufus ) was more frequent than expected. Different EcM fungi foraged at different spatial scales.

Summary• Spatial analysis was used to explore the distribution of individual species in an ectomycorrhizal (ECM) fungal community to address: whether mycorrhizas of individual ECM fungal species were patchily distributed, and at what scale; and what the causes of this patchiness might be.• Ectomycorrhizas were extracted from spatially explicit samples of the surface organic horizons of a pine plantation. The number of mycorrhizas of each ECM fungal species was recorded using morphotyping combined with internal transcribed spacer (ITS) sequencing. Semivariograms, kriging and cluster analyses were used to determine both the extent and scale of spatial autocorrelation in species abundances, potential interactions between species, and change over time.• The mycorrhizas of some, but not all, ECM fungal species were patchily distributed and the size of patches differed between species. The relative abundance of individual ECM fungal species and the position of patches of ectomycorrhizas changed between years.• Spatial and temporal analysis revealed a dynamic ECM fungal community with many interspecific interactions taking place, despite the homogeneity of the host community. The spatial pattern of mycorrhizas was influenced by the underlying distribution of fine roots, but local root density was in turn influenced by the presence of specific fungal species.

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Microbial ecology has made large advances over the last decade, mostly because of improvements in molecular analysis techniques that have enabled the detection and identification of progressively larger numbers of microbial species. However, determining the ecological patterns and processes taking place in communities of microbes remains a significant challenge. Are communities randomly assembled through dispersal and priority effects, or do species interact with each other leading to positive and negative associations? For mycorrhizal fungi, evidence is accumulating that stochastic and competitive interactions between species may both have a role in shaping community structure. Could the methodological approach, which is often incidence based, impact the outcomes detected? Here, we applied an incidence-based Terminal Restriction Fragment Length Polymorphism (T-RFLP) database approach to examine species diversity and ecological interactions within a community of ectomycorrhizal (ECM) fungi. Co-occurrence analysis revealed that the ECM community colonizing root tips was strongly structured by competitive interactions, or ecological processes generating a similar spatial pattern, rather than neutral processes. Analysis of β-diversity indicated that community structure was significantly more similar (spatially autocorrelated) at distances equal to or <3.41 m. The eight most frequently encountered species in the root tip community of ECM fungi displayed significant competitive interactions with at least one other species, showing that the incidence-based approach was capable of detecting this sort of ecological information.

In many semi-natural and natural ecosystems, mycorrhizal fungi are the most abundant and functionally important group of soil micro-organisms. They are almost wholly dependent on their host plants to supply them with photosynthate in return for which they enable the plant to access greater quantities of nutrients. Thus, there is considerable potential for plant communities to regulate the structure and function of mycorrhizal communities. This paper reviews some of the key recent developments that have enabled the influence of plant species richness, composition, and age on mycorrhizal communities in boreal forests and temperate grassland to be determined. It discusses the emerging evidence that, in some situations, plant species richness is related to mycorrhizal species richness, in contrast to previous thinking. The paper also includes some preliminary data on the effect of host stand age on root-associated basidiomycete communities. It concludes by highlighting some of the new methodological advances that promise to unravel the linkages between mycorrhizal diversity and their function in situ.

SummaryEctomycorrhizal (ECM) mycelium is a key component of the ectomycorrhizal symbiosis, yet we know little regarding the fine-scale diversity and distribution of mycelium in ECM fungal communities.We collected four 20 9 20 9 2-cm 3 (800-cm 3 ) slices of Scots pine (Pinus sylvestris) forest soil and divided each into 100 2 9 2 9 2-cm 3 (8-cm 3 ) cubes. The presence of mycelium of ECM fungi was determined using an internal transcribed spacer (ITS) database terminal restriction fragment length polymorphism (T-RFLP) approach. As expected, many more ECM fungi were detected as mycelium than as ectomycorrhizas in a cube or slice. More surprisingly, up to one-quarter of the 43 species previously detected as ectomycorrhizas over an area of 400 m 2 could be detected in a single 8-cm 3 cube, and up to three-quarters in a single 800-cm 3 slice. ECM mycelium frequency decreased markedly with depth and there were distinct 'hotspots' of mycelium in the moss/F1 layer. Our data demonstrate a high diversity of ECM mycelium in a small (8-cm 3 ) volume of substrate, and indicate that the spatial scale at which ECM species are distributed as mycelium may be very different from the spatial scale at which they are distributed as tips.

Summary1. Spatial variation and covariation in host-plant quality, herbivore abundance and herbivore mortality were examined across the natural geographical range in Europe of holly Ilex aquifolium and the host-specific holly leaf-miner Phytomyza ilicis. 2. Although measures of host-plant quality showed substantial between-site variation, no simple spatial pattern in any of the measures (only phosphorus content and leaf mass showed correlations with latitude, longitude or altitude) was detected, and few correlations with tree or local site characteristics. 3. In contrast, measures of the abundance of the leaf-miner exhibited marked spatial patterns, resulting in a lack of simple covariance between leaf-miner abundance and host-plant quality. 4. Different apparent mortalities of the leaf-miner exhibited varied spatial patterns in their intensity, but no evidence of range-wide density dependence, again resulting in few patterns of covariance between intensity of mortality and measures of host-plant quality. 5. The population dynamics of the holly leaf-miner across its geographical range are complex. At any site, the mortality that a population experiences is the sum of largely independent yet spatially structured components, against a background of varying hostplant quality. Despite lacking any marked spatial structure, host-plant quality may have important local effects. These are difficult to detect regionally, and thus may principally contribute noise to regional patterns of levels of oviposition, abundance and mortality.

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