Role Of Ectomycorrhizal Fungi Research Articles

Facilitative and competitive interactions between mycorrhizal and nonmycorrhizal plants in an extremely phosphorus-impoverished environment: role of ectomycorrhizal fungi and native oomycete pathogens in shaping species coexistence.

Nonmycorrhizal cluster root-forming species enhance the phosphorus (P) acquisition of mycorrhizal neighbours in P-impoverished megadiverse systems. However, whether mycorrhizal plants facilitate the defence of nonmycorrhizal plants against soil-borne pathogens, in return and via their symbiosis, remains unknown. We characterised growth and defence-related compounds in Banksia menziesii (nonmycorrhizal) and Eucalyptus todtiana (ectomycorrhizal, ECM) seedlings grown either in monoculture or mixture in a multifactorial glasshouse experiment involving ECM fungi and native oomycete pathogens. Roots of B. menziesii had higher levels of phytohormones (salicylic and jasmonic acids, jasmonoyl-isoleucine and 12-oxo-phytodienoic acid) than E. todtiana which further activated a salicylic acid-mediated defence response in roots of B. menziesii, but only in the presence of ECM fungi. We also found that B. menziesii induced a shift in the defence strategy of E. todtiana, from defence-related secondary metabolites (phenolic and flavonoid) towards induced phytohormone response pathways. We conclude that ECM fungi play a vital role in the interactions between mycorrhizal and nonmycorrhizal plants in a severely P-impoverished environment, by introducing a competitive component within the facilitation interaction between the two plant species with contrasting nutrient-acquisition strategies. This study sheds light on the interplay between beneficial and detrimental soil microbes that shape plant-plant interaction in severely nutrient-impoverished ecosystems.

The interactive effects of soil fertility and tree mycorrhizal association explain spatial variation of diversity–biomass relationships in a subtropical forest

Abstract Observed biodiversity–ecosystem function (BEF) relationships are highly variable, particularly in natural forests. However, our understanding of the factors that generate these often contradictory patterns, especially the role of different mycorrhizal associations, is still limited. By relating tree species richness and above‐ground biomass (AGB) in a fully mapped 24‐ha subtropical forest dynamics plot, we evaluated the impacts of soil fertility and tree mycorrhizal type in mediating BEF relationships at multiple spatial scales. Our results demonstrate a highly positive total richness effect on AGB for arbuscular mycorrhizal (AM) trees but a negative effect on AGB for ectomycorrhizal (EcM) trees, and their relationships were highly spatial scale dependent. However, the observed BEF relationships turned into positive at small spatial scales (i.e. 10 and 20 m) after controlling for other confounding factors (i.e. topography, soil fertility and AM proportion). In addition, we found significant interactions between soil fertility and species richness on AGB. Specifically, the positive effect of total species richness on AGB for major mycorrhizal types gradually weakened with increasing soil fertility, while the positive effect of EcM species richness on AM AGB gradually enhanced at small spatial scales, suggesting the observed diversity effects can be largely attributed to resource niche complementarity and the role of EcM fungi. Synthesis. We conclude that the variable BEF relationships among forest communities could be explained by spatial variation in abiotic environments and community mycorrhizal composition because different types of symbionts perform different nutrient uptake strategies and ability in protection from antagonists. Our findings provide novel insights into the understanding of the variation in the shape of BEF relationships in natural forests, which is critical for forest management, conservation and restoration in a changing world.

Species-level identity of Pisolithus influences soil phosphorus availability for host plants and is moderated by nitrogen status, but not CO2

Trees are dependent on the activity of soil microorganisms, including mutualistic ectomycorrhizal (ECM) fungi and soil-dwelling bacteria, for access to phosphorus (P). While P is a key limiting nutrient in temperate and other forest ecosystems, our understanding of the contributions of ECM fungi to plant P nutrition and cycling are unclear. Further complicating our understanding of these processes are the combined effects of fungal species and future climate scenarios and soil nutrient availability.In this study we characterised how the ECM fungi Pisolithus albus and Pisolithus microcarpus influenced the amount of plant-available P in soils and plant P content of Eucalyptus grandis. We explored how these fungi influence P cycling by studying their relative P-solubilising and P-mineralising abilities and examining their impact on P cycling gene abundance in the soil bacterial community. These were investigated under different levels of nitrogen addition and atmospheric CO2 to understand how these processes may be impacted by future anthropogenic and climactic change. While inoculation with either P. albus or P. microcarpus resulted in an increase in plant-available P in soil, the amount of plant-available P mobilised was species-specific. This observation was supported by differences in the in vitro P-mobilising abilities of the two fungi. P. albus and P. microcarpus also favoured bacterial communities characterised by a greater abundance of glucose dehydrogenase gene copies for inorganic P solubilisation, complementing the strengths of the ECM fungi in organic P mineralisation and suggesting a distinction in the roles of ECM fungi and bacteria in P cycling. Furthermore, both nitrogen and CO2 levels impacted these P cycling outcomes, often in a species-specific manner. Our findings expand the current understanding of P cycling between forest trees, ECM fungi and soil bacteria, and have important implications for estimations of future anthropogenic impacts on forest ecosystems.

Back to Roots: The Role of Ectomycorrhizal Fungi in Boreal and Temperate Forest Restoration

Temperate and boreal forests are increasingly suffering from anthropic degradation. Ectomycorrhizal fungi (EMF) are symbionts with most temperate and boreal forest trees, providing their hosts with soil nutrients and water in exchange for plant carbon. This group of fungi is involved in woody plants’ survival and growth and helps plants tolerate harsh environmental conditions. Here, we describe the current understanding of how EMF can benefit temperate and boreal forest restoration projects. We review current evidence on promising restoration plans that actively use EMF in sites contaminated with heavy metals, affected by soil erosion, and degraded due to clearcut logging and wildfire. We discuss the potential role of this group of fungi for restoring sites invaded by non-native plant species. Additionally, we explore limitations, knowledge gaps, and possible undesired outcomes of the use of EMF in forest restoration, and we suggest how to further incorporate this fungal group into forest management. We conclude that considering EMF – host interactions could improve the chances of success of future restoration programs in boreal and temperate forests.

Ectomycorrhizal utilization of different phosphorus sources in a glacier forefront in the Italian Alps

In deglaciated surfaces, lithology influences habitat development. In particular, serpentinite inhibits soil evolution and plant colonization because of insufficient phosphorus (P) content, among other stressful properties. In nutrient-poor environments, ectomycorrhizal fungi (EMF) play a key role exploring the soil for P beyond the rhizosphere. In this study, we followed the role of EMF in accessing inorganic and organic P along two proglacial soil chronosequences in the Alps (NW Italy), respectively characterized by pure serpentinite till and serpentinite mixed with 10% of gneiss, and colonized by European Larch. The access to inorganic and organic P forms by EMF was studied using specific mesh-bags for fungal hyphae entry, filled with quartz sand and inorganic phosphate (Pi) or myo-inositolhexaphosphate (InsP6) adsorbed onto goethite. They were incubated over 13 months at the organic/mineral horizon interface. After harvesting, EMF colonization via ergosterol analysis and the amount of P and Fe removed from mesh bags were measured. Ergosterol increased along the two chronosequences with slightly greater values on serpentinite and in Pi-containing bags. Up to 65% of Pi was removed from mesh-bags, only partly accompanied by a parallel release of Fe. The amount of InsP6 released was instead less than 45% and mostly removed with goethite. The results suggest that, in extremely P-poor environments, EMF are able to release both inorganic and organic P forms from highly stabilized associations.

Does ectomycorrhiza have a universal key role in the formation of soil organic matter in boreal forests?

Forest soil organic matter (SOM) is an important dynamic store of C and N, which releases plant available N and the greenhouse gases CO2 and N2O. Early stages of decomposition of recent plant litters are better known than the formation of older and more stable soil pools of N and C, in which case classic theory stated that selective preservation of more resistant plant compounds was important. Recent insights heighten that all plant matter becomes degraded and that older SOM consists of compounds proximally of microbial origin. It has been proposed that in boreal forests, ectomycorrhizal fungi (ECMF), symbionts of trees, are actively involved in the formation of slowly-degrading SOM.We characterized SOM in the mor-layer along a local soil N supply gradient in a boreal forest, a gradient with large variations in chemical and biological characteristics, notably a decline in the biomass of ECMF in response to increasing soil N supply.We found contrasting and regular patterns in carbohydrates, lignin, aromatic carbon, and in N-containing compounds estimated by solid-state 13C and 15N nuclear magnetic resonance (NMR) spectroscopy. These occurred along with parallel changes in the natural abundances of the stable isotopes 13C and 15N in both bulk SOM and extracted fractions of the SOM. The modelled “bomb-14C″ age of the lower layers studied ranged between 15 years at the N-poor end, to 70 years at the N-rich end of the gradient. On average half the increase in δ13C with soil depth (and hence age) of the mor-layer can be attributed to soil processes and the other half to changes in the isotopic composition of the plant C inputs. There was a decrease in carbohydrates (O-alkyl C) with increasing depth. This supports the classical hypothesis of declining availability of easily decomposable substrates to microorganisms with increasing soil depth and age. The observed increase in δ13C with depth, however, speaks against the idea of selective preservation of more resistant plant compounds like lignin. Furthermore, from the N-poor to the N-rich end the difference between 15N in plant litter N and N in the deeper part of the mor-layer, the H-layer, decreased in parallel with a decline in ECMF.The latter provides evidence that the role of ECMF as major sink for N diminishes, and hence their potential role in SOM stabilization, when the soil N supply increases. At the N-rich end, where bacteria dominate over fungi, other agents than ECMF must be involved in the large build-up of the H-layer with the slowest turnover rate found along the gradient.

Variable retention harvesting influences belowground plant-fungal interactions of Nothofagus pumilio seedlings in forests of southern Patagonia.

BackgroundThe post-harvest recovery and sustained productivity of Nothofagus pumilio forests in Tierra del Fuego may be affected by the abundance and composition of ectomycorrhizal fungi (EMF). Timber harvesting alters EMF community structure in many managed forests, but the impacts of harvesting can vary with the management strategy. The implementation of variable retention (VR) management can maintain, increase, or decrease the diversity of many species, but the effects of VR on EMF in the forests of southern Patagonia have not been studied, nor has the role of EMF in the regeneration process of these forests.MethodsWe evaluated the effects of VR management on the EMF community associated with N. pumilio seedlings. We quantified the abundance, composition, and diversity of EMF across aggregate (AR) and dispersed (DR) retention sites within VR managed areas, and compared them to primary forest (PF) unmanaged stands. EMF assemblage and taxonomic identities were determined by ITS-rDNA sequencing of individual root tips sampled from 280 seedlings across three landscape replicates. To better understand seedling performance, we tested the relationships between EMF colonization, EMF taxonomic composition, seedling biomass, and VR treatment.ResultsThe majority of EMF taxa were Basidiomycota belonging to the families Cortinariaceae (n = 29), Inocybaceae (n = 16), and Thelephoraceae (n = 8), which was in agreement with other studies of EMF diversity in Nothofagus forests. EMF richness and colonization was reduced in DR compared to AR and PF. Furthermore, EMF community composition was similar between AR and PF, but differed from the composition in DR. EMF community composition was correlated with seedling biomass and soil moisture. The presence of Peziza depressa was associated with higher seedling biomass and greater soil moisture, while Inocybe fibrillosibrunnea and Cortinarius amoenus were associated with reduced seedling biomass and lower soil moisture. Seedling biomass was more strongly related to retention type than EMF colonization, richness, or composition.DiscussionOur results demonstrate reduced EMF attributes and altered composition in VR treatments relative to PF stands, with stronger impacts in DR compared to AR. This suggests that VR has the potential to improve the conservation status of managed stands by supporting native EMF in AR. Our results also demonstrate the complex linkages between retention treatments, fungal community composition, and tree growth at individual and stand scales.

Rapid Response by the Ectomycorrhizal (ECM) Community of a Lodgepole Pine Forest to Diesel Application as Indicated by Laccase Gene Fragment Diversity

A combination of field baiting and molecular methods was used to identify basidiomycete fungi that are able to withstand conditions within diesel contamination in a pine forest soil. Diesel was applied to 3, 1 meter x 1 meter blocks, which penetrated to a depth of 4 cm. After two weeks fungi that exhibited positive growth responses were identified by amplifying laccase (phenol oxidase) gene fragments using primers specific to basidiomycete laccase genes. The internal transcribed spacer (ITS) region of the nuclear ribosomal DNA (nrDNA) gene repeat was amplified as well to provide a broad community screen, to indicate the pool of basidiomycete fungi that could respond to diesel application. Results indicated that ectomycorrhizal (ECM) fungi in the genera Russula, Piloderma and the ECM species Tricholoma saponaceum (rather than wood-rotting basidiomycetes) responded rapidly to diesel application. These results support recent hypotheses regarding the ecological role of ECM fungi in carbon cycling via exploitation of short chain phenolic carbon compounds. Further the ECM fungi that responded correspond roughly to classification of ECM exploration type, a criterion that describes ECM fungi on the basis of their hyphal growth patterns and potential for enzymatic activity. Finally, because it is apparent that these ECM fungi can survive and express laccase genes under conditions created by diesel contamination, these data provide new models for phytoremediation and site restoration strategies that utilize ECM fungi and pines.

Iron ore weathering potentials of ectomycorrhizal plants

Plants in association with soil microorganisms play an important role in mineral weathering. Studies have shown that plants in symbiosis with ectomycorrhizal (ECM) fungi have the potential to increase the uptake of mineral-derived nutrients. However, it is usually difficult to study many of the different factors that influence ectomycorrhizal weathering in a single experiment. In the present study, we carried out a pot experiment where Pinus patula seedlings were grown with or without ECM fungi in the presence of iron ore minerals. The ECM fungi used included Pisolithus tinctorius, Paxillus involutus, Laccaria bicolor and Suillus tomentosus. After 24 weeks, harvesting of the plants was carried out. The concentration of organic acids released into the soil, as well as potassium and phosphorus released from the iron ore were measured. The results suggest that different roles of ectomycorrhizal fungi in mineral weathering such as nutrient absorption and transfer, improving the health of plants and ensuring nutrient circulation in the ecosystem, are species specific, and both mycorrhizal roots and non-mycorrhizal roots can participate in the weathering process of iron ore minerals.

Laccaria bicolor S238N improves Scots pine mineral nutrition by increasing root nutrient uptake from soil minerals but does not increase mineral weathering

The role of ectomycorrhizal fungi on mineral nutrient mobilization and uptake is crucial for tree nutrition and growth in temperate forest ecosystems. By using a “mineral weathering budget” approach, this study aims to quantify the effect of the symbiosis with the ectomycorrhizal model strain Laccaria bicolor S238N on mineral weathering and tree nutrition, carrying out a column experiment with a quartz/biotite substrate. Each column was planted with one Scots pine (Pinus sylvestris L.) non-mycorrhizal or mycorrhizal with L. bicolor, with exception of the abiotic control treatment. The columns were continuously supplied with a nutrient-poor solution. A mineral weathering budget was calculated for K and Mg. The pine shoot growth was significantly increased (73%) when plants were mycorrhizal with L. bicolor. Whatever their mycorrhizal status, pines increased mineral weathering by factors 1.5 to 2.1. No difference between non-mycorrhizal and mycorrhizal pine treatments was revealed, however, mycorrhizal pines assimilated significantly more K and Mg. This suggests that in our experimental conditions, L. bicolor S238N improved shoot growth and K and Mg assimilation in Scots pine mainly by increasing the uptake of dissolved nutrients, linked to a better exploration and exploitation of the soil by the mycorrhizal roots.

Possible role of ectomycorrhizal fungi in cycling of aluminium in podzols

Budget studies in boreal podzols indicate a considerable upward transport of aluminium (Al) from the mineral soil into the organic horizon. In this paper we studied if ectomycorrhizal (EcM) fungi can be involved in this upward transport via their extramatrical hyphae. We tested the use of gallium (Ga) as proxy for Al. Transport of Al through EcM hyphae was studied in vitro in a two-compartment Petri dish system. Two of the five fungal isolates tested transported Al. Using Ga instead of Al revealed the same trend in these systems, confirming the use of Ga as proxy for Al. Upward transport of Ga was studied in an artificial podzol. Pinus sylvestris seedlings were colonised by a natural community of EcM fungi from fresh forest soil. Gallium addition to the mineral soil led to increased Ga content in roots in the organic horizon and in the shoot. Upward Ga allocation was significantly higher when roots were excluded from the mineral soil by a mesh, only allowing fungal mycelium to grow through. We conclude that at least some EcM fungi transport Al and that Ga, and probably also Al, can be transported upwards by EcM fungal hyphae in a podzol system. These findings support the hypothesis that EcM fungi play a role in upward transport of Al in podzols.

The role of ectomycorrhizal fungi in alleviating pine decline in semiarid sandy soil of northern China: an experimental approach

The decline of Mongolian pine (Pinus sylvestris var. mongolica) trees on sandy land in northern China has caused serious ecological concerns. Mongolian pine is an ectomycorrhizal fungus (ECM)-dependent species. Three ECM species (Boletus sp., Lactarius deliciosus and L.sp.) were collected from Mongolian pine plantation stands to test their beneficial effects on Mongolian pine seedlings and their responses to environmental factors such as pH, drought stress and temperature. The results indicated that ECM inoculation significantly increased the rate of ECM colonization and the length of seedling shoots. The three ECM could grow in a pH range from 4 to 7, but did not grow under heavy drought stress (−1.53 MPa). High temperatures (over 37 °C) caused death of ECM. When related to soil pH, soil water content and temperature in the Mongolian pine plantations, water conditions and temperature were unfavorable for ECM growth in surface soil, but suitable in deeper soil. Therefore, it was concluded that the failure of natural regeneration in Mongolian pine plantations might be influenced by the lack of ECM in the surface soil because of high temperatures causing ECM death. Moreover, the majority of the root area is distributed in deeper soil, which alleviates the stresses on ECM development and arrests pine decline; this is beneficial for tree growth.

Introduction to Molecular Analysis of Ectomycorrhizal Communities

A number of methods are available for those researchers considering the addition of molecular analyses of ectomycorrhizal (EcM) fungi to their research projects and weighing the various approaches they might take. Analyzing natural EcM fungal communities has traditionally been a highly skilled, time‐consuming process relying heavily on exacting morphological characterization of EcM root tips. Increasingly powerful molecular methods for analyzing EcM communities make this area of research available to a much wider range of researchers. Ecologists can gain from the body of work characterizing EcM while avoiding the requirement for exceptional expertise by carefully combining elements of traditional methods with the more recent molecular approaches. A cursory morphological analysis can yield a traditional quantification of EcM fungi based on tip numbers, a unit with functional and historical significance. Ectomycorrhizal root DNA extracts may then be analyzed with molecular methods widely used for characterizing microbiota. These range from methods applicable only to the simple mixes resulting from careful morphotyping, to community‐oriented methods that identify many types in mixed samples as well as provide an estimate of their relative abundances. Extramatrical hyphae in bulk soil can also be more effectively studied, extending characterization of EcM fungal communities beyond the rhizoplane. The trend toward techniques permitting larger sample sets without prohibitive labor and time requirements will also permit us to more frequently address the issues of spatial and temporal variability and better characterize the roles of EcM fungi at multiple scales.

Ectomycorrhizal Fungi and Associated Bacteria Provide Protection Against Heavy Metals in Inoculated Pine (Pinus Sylvestris L.) Seedlings

The roles of ectomycorrhizal fungi and bacteria associated with corresponding fungal species in distribution of heavy metals within roots and shoots of inoculated pine (Pinus sylvestris L.) seedlings were determined in this study. The mycorrhizal fungi forming different morphotypes were identified by PCR-RFLP using respective primers for an internal spacer transcribed region (ITS) of fungal rDNA. Amongst five fungal species detected, three were identified as Scleroderma citrinum, Amanita muscaria and Lactarius rufus. These fungi used for inoculation of pine seedlings significantly reduced translocation of Zn(II), Cd(II) or Pb(II) from roots to shoots, and the pattern of metal-accumulation was dependent on the fungal species. Ectomycorrhizae-associated bacteria identified as Pseudomonas were used as an additional component of the pine inoculation. These dual root inoculations resulted in higher accumulation of the metals, especially Zn(II), in the roots compared to the inoculation with fungal species alone. Consequently, dual inoculation of pine seedlings could be a suitable approach for plant protection against heavy metals and successful planting of metal-polluted soils.

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The potential role of ectomycorrhizal fungi in determining Douglas-fir resistance to defoliation by the western spruce budworm (Lepidoptera: Tortricidae).

There is phenotypic variation among individual trees of interior Douglas-fir (Pseudotsuga menziesii var. glauca [Beissn.] Franco) in their resistance to defoliation by the western spruce budworm (Choristoneura occidentalis Freeman). We evaluated the potential role of ectomycorrhizal fungi in determining this resistance using half-sib seedlings derived from parent trees that are resistant versus susceptible to budworm defoliation in the field. The seedlings were inoculated with Laccaria bicolor ectomycorrhizal fungi, fertilized, or untreated. Approximately 48 d after treatment, late-instar larvae from a nondiapausing laboratory colony of C. occidentalis were allowed to feed on pairs of resistant versus susceptible seedlings for 1 wk. Chemical analyses of current-year shoots for nitrogen (N), phosphorus (P), magnesium (Mg), and zinc (Zn) indicated that the fungus increased foliar concentrations of P and Mg in resistant seedlings, but it did not increase their growth rate. However, L. bicolor had no effect on foliar concentrations of P or Mg in susceptible seedlings, even though seedling growth rates increased slightly in response to the inoculation. L. bicolor had no effect on foliar levels of N or Zn in any of the seedlings. As expected, fertilization increased levels of N and P in the foliage of both resistant and susceptible seedlings, but it did not affect levels of Mg and Zn. Surprisingly, the fertilizer treatment had no effect on seedling growth rates. Despite these differences, late-instar budworms showed no feeding preference among untreated, mycorrhizal, or fertilized seedlings. The fact that seedlings from resistant versus susceptible Douglas-firs responded differently to the L. bicolor treatment lends preliminary support to the hypothesis that ecotmycorrhizae might play a role in Douglas-fir resistance to damage from the western spruce budworm. Finally, differences in foliar concentrations of N and P among untreated seedlings from different maternal trees suggested that foliar nutritional chemistry is influenced by the tree's genotype.

Solubilisation and colonisation of wood ash by ectomycorrhizal fungi isolated from a wood ash fertilised spruce forest

In Sweden application of granulated wood ash has been suggested as a method to supplement nutrient loss resulting from harvesting of forest residues for bioenergy production. Mycelia of two ectomycorrhizal fungi Piloderma sp. 1 and Ha-96-3, were commonly found to colonise ash granules in a wood ash fertilised spruce forest. Thirty-eight fungal isolates were selected from 10 taxa to investigate the possible role of different ectomycorrhizal fungi in nutrient mobilisation from ash. The taxa were Cenococcum geophilum Fr., Piloderma croceum Erikss. and Hjortst., Piloderma sp. 1, Thelephora terrestris (Ehrenb.) Fr., Tylospora fibrillosa Donk, and five unidentified species, all originating from a wood ash fertilised spruce forest. The isolates were tested for their ability to solubilise tricalcium phosphate (TCP) or hardened wood ash (HWA) in vitro. Ha-96-3, P. croceum and Piloderma sp. 1 were the only taxa which solubilised TCP. Abundant calcium oxalate crystals were formed in TCP and HWA plates with Piloderma sp. 1. Ha-96-3 and two isolates of P. croceum produced intermediate amounts of crystals. Ha-96-1 and T. fibrillosa produced low amounts of crystal but no crystal formation was observed by any of the other isolates. Piloderma sp. 1 from HWA plates had significantly higher concentrations of P, compared to P. croceum or Ha-96-3. Piloderma sp. 1 and P. croceum were further tested for their ability to colonise wood ash in microcosms containing intact mycorrhizal associations. After 7 months Piloderma sp. 1 colonised ash amended patches with a dense, mat like mycelium, whereas P. croceum mycelia avoided the ash patches. Possible differences between these fungi in patterns of carbon allocation were investigated by labelling seedlings with 14CO 2. Piloderma sp. 1 mycelia allocated significantly more 14C to ash patches than P. croceum. P. croceum allocated relatively more 14C to control patches than to the ash patches. The possible role of ectomycorrhizal fungi in mobilisation of nutrients from wood ash is discussed.

Solubilisation and colonisation of wood ash by ectomycorrhizal fungi isolated from a wood ash fertilised spruce forest.

In Sweden application of granulated wood ash has been suggested as a method to supplement nutrient loss resulting from harvesting of forest residues for bioenergy production. Mycelia of two ectomycorrhizal fungi Piloderma sp. 1 and Ha-96-3, were commonly found to colonise ash granules in a wood ash fertilised spruce forest. Thirty-eight fungal isolates were selected from 10 taxa to investigate the possible role of different ectomycorrhizal fungi in nutrient mobilisation from ash. The taxa were Cenococcum geophilum Fr., Piloderma croceum Erikss. and Hjortst., Piloderma sp. 1, Thelephora terrestris (Ehrenb.) Fr., Tylospora fibrillosa Donk, and five unidentified species, all originating from a wood ash fertilised spruce forest. The isolates were tested for their ability to solubilise tricalcium phosphate (TCP) or hardened wood ash (HWA) in vitro. Ha-96-3, P. croceum and Piloderma sp. 1 were the only taxa which solubilised TCP. Abundant calcium oxalate crystals were formed in TCP and HWA plates with Piloderma sp. 1. Ha-96-3 and two isolates of P. croceum produced intermediate amounts of crystals. Ha-96-1 and T. fibrillosa produced low amounts of crystal but no crystal formation was observed by any of the other isolates. Piloderma sp. 1 from HWA plates had significantly higher concentrations of P, compared to P. croceum or Ha-96-3. Piloderma sp. 1 and P. croceum were further tested for their ability to colonise wood ash in microcosms containing intact mycorrhizal associations. After 7 months Piloderma sp. 1 colonised ash amended patches with a dense, mat like mycelium, whereas P. croceum mycelia avoided the ash patches. Possible differences between these fungi in patterns of carbon allocation were investigated by labelling seedlings with 14CO(2). Piloderma sp. 1 mycelia allocated significantly more 14C to ash patches than P. croceum. P. croceum allocated relatively more 14C to control patches than to the ash patches. The possible role of ectomycorrhizal fungi in mobilisation of nutrients from wood ash is discussed.

Influence of Ectomycorrhiza on the Structure of Detrital Food Webs in Pine Rhizosphere

Trees infected with ectomycorrhizal (EM) fungi are known to direct several times more energy into the soil than non-ectomycorrhizal trees. Since energy-rich substrates are required by most biological processes, it is widely speculated that the flow of carbon from plants through EM mycelia into soils should have a wide range of effects in the below-ground milieu. In this study we investigated whether EM fungi of effects in the below-ground milieu. In this study we investigated whether EM fungi of Scots pine (Pinus sylvestris) seedlings exert a short-term influence on the biomass and composition of a detrital food web consisting of up to three trophic levels. The experiment was conducted in microcosms with raw humus, perlite and sandy soil (1:1:1; vol.). The soil was defaunated. reinoculated with 10 species of soil bacteria. and 11 species of saprophytic soil fungi, and pine seedlings, either infected or non-infected with six taxa of EM fungi, were separately planted in the microcosms. Five different food webs were established: 1) saprophytic microbes alone. 2) as 1) but with two species of bacterial-feeding nematodes. 3) as 2) but two species of fungal-feeding nematodes included. 4) as 2) but with predatory nematodes, and 5) as 3) but with predatory nematodes. The microcosms were incubated in a climate chamber with varying illumination and temperature regimes for two annual cycles of the pine. After 37 weeks, ca 15 times more fungal biomass was detected on pine roots growing in the systems inoculated with EM fungi than in non-inoculated systems, and there was a significantly greater total biomass of pines in the EM systems. Despite this clearly enhanced autotroph production, neither the total nematode biomass nor the length of the food chain were affected by the EM fungi. The presence of nematodes. independent of the composition of this fauna, enhanced the production of pine biomass significantly, but only in the absence of mycorrhizal fungi. Neither the species composition nor the trophic group architecture of the fauna influenced EM production or growth of EM infected pines, except for fungal-feeding nematodes which had a slight negative influence on the biomass of EM fungi. Our results infer that the role of EM fungi in affecting the amount of energy entering the soils is significant in the long run only, i.e. through increased litter production. We hypothesize that the short-term insensitivity of the decomposer food web to the presence of EM fungi reflects the nature of EM fungi as an efficient sink, preventing the additional production of plant-derived photosynthates from-reaching the organisms of the detrital food web.

Spatiotemporal patterns in ectomycorrhizal populations

To understand the functioning and ecological roles of ectomycorrhizal fungi in natural ecosystems, it is necessary to have adequate knowledge of the spatial distribution of individual mycelial systems in populations and communities and how this distribution may persist or vary with time. However, this issue has attracted relatively little attention until recently. Moreover, the limited information available is mostly based on the distribution of sporocarps, which is at best an unreliable indicator of the location and activity of mycelia. More useful information can be obtained using somatic and sexual incompatibility tests, as well as molecular markers to trace the distribution of individual genets over a range of spatial and temporal scales. For example, it has been possible using this approach to demonstrate that while young populations tend to consist of numerous small mycelia, individuals in older populations tend to be fewer and larger but heterogeneous in scale. It has also been possible to verify the persistence over several years of mycorrhizal mycelial individuals. Such findings represent only the first step in the study of the spatiotemporal dynamics of ectomycorrhizal fungi, which promises to be a rich and important field for future research. Concepts concerning the process and mechanisms likely to affect distribution patterns are discussed. Key words: ectomycorrhiza, population structure, population dynamics, spatiotemporal patterns.