Ectomycorrhizal Fungi Taxa Research Articles

Spore viability and germination of some ectomycorrhizal fungi from New Zealand and implications for forest restoration

ABSTRACT Ectomycorrhizal fungi (EMF) are critical to the establishment of many plant species and an important consideration in ecological restoration of southern beech (Nothofagaceae) forest. However, information on spore viability and storage is lacking for EMF taxa associated with southern beech. This study tested the viability and germination of spores from fruiting bodies collected during autumn and spring from mountain beech forest, Otago, New Zealand. Nuclear ribosomal ITS sequences matched autumn collections to the EMF genera Cortinarius, Inocybe and Russula, but all spring collections were an undescribed hypogeous taxon resembling the native EMF genus Hysterangium, referred to here as Hysterangiaceae ‘Motatapu’. We investigated propidium iodide as a spore viability test, and compared spore germination in water vs glucose, in different temperature and light regimes, and between freshly collected spores and spores from fruiting bodies dried at 30°C or frozen at −20°C. Propidium iodide did not stain all devitalised spores, so may be unreliable for quantifying viability of fresh spores. Spore germination in water was <6% for all genera and <2% for most taxon × treatment combinations. Fresh spores of Hysterangiaceae ‘Motatapu’ suspended in 4°C water showed higher germination than at 20°C; excluding light had no significant effect. Spores of the same taxon suspended in 10% and 20% glucose showed lower germination in comparison to water and showed deformations. Germination percentages of all taxa decreased with storage, but spores of some taxa retained viability for 120 days in 4°C water suspensions. Spores of Hysterangiaceae ‘Motatapu’ showed the least loss of viability with storage of all taxa investigated. For the purposes of storing EMF material for use as inoculum, we recommend drying fruiting bodies at 30°C for storage, then preparing fresh spore suspensions in water when inoculum is required.

Elevated CO2 and O3 effects on ectomycorrhizal fungal root tip communities in consideration of a post-agricultural soil nutrient gradient legacy.

Despite the critical role of EMF in nutrient and carbon (C) dynamics, combined effects of global atmospheric pollutants on ectomycorrhizal fungi (EMF) are unclear. Here, we present research on EMF root-level community responses to elevated CO2 and O3. We discovered that belowground EMF community richness and similarity were both negatively affected by CO2 and O3, but the effects of CO2 and O3 on EMF communities were contingent on a site soil pH and cation availability gradient. These results contrast with our previous work showing a strong direct effect of CO2 and O3 on sporocarp community dynamics and production. We discuss the possible role of carbon demand and allocation by EMF taxa in the discrepancy of these results. EMF communities were structured by a legacy of spatially defined soil properties, changing atmospheric chemistry and temporal dynamics. It is therefore necessary to understand global change impacts across multiple environmental gradients and spatiotemporal scales.

Nitrogen isotopes in ectomycorrhizal sporocarps correspond to belowground exploration types

Nitrogen isotope values (δ15N) are higher in ectomycorrhizal fungi than in their plant hosts but the wide variability in δ15N among sporocarps of different fungal taxa is unexplained. We propose that fungal δ15N reflects sequestration of fungal nitrogen to build fungal biomass, and should accordingly reflect fungal exploration strategies and hyphal properties. To test this, we compared δ15N to exploration types, hyphal hydrophobicity, and the presence of rhizomorphs in ectomycorrhizal species from surveys at four sites in temperate and boreal coniferous forests. Fungi with exploration types of high biomass, such as long-distance (e.g., Suillus), medium-distance mat (e.g., Hydnellum), and medium-distance fringe (e.g., Cortinarius) were 4–7‰ more enriched in 15N than fungi with exploration types of low biomass [medium-distance smooth (e.g., Amanita), short-distance (e.g., Inocybe), and contact (e.g., Hygrophorus)]. High biomass types comprised 79% (Aheden, northern Sweden), 65% (Deer Park, Pacific Northwest, USA), 45% (Stadsskogen, central Sweden), and 39% (Hoh, Pacific Northwest, USA) of ectomycorrhizal species, with these types more prevalent at sites of lower nitrogen availability. Species with hydrophobic hyphae or with rhizomorphs were 3–4‰ more enriched in 15N than taxa with hydrophilic hyphae or without rhizomorphs. The consistency of these patterns suggest that δ15N measurements could provide insights into belowground functioning of poorly known taxa of ectomycorrhizal fungi and into relative fungal biomass across ectomycorrhizal communities.

Uptake of an amino acid by ectomycorrhizal fungi in a boreal forest

We assessed the degree to which ectomycorrhizal fungi exploit organic nitrogen in situ. In an Alaskan boreal forest, we identified pairs of sporocarps from five taxa of ectomycorrhizal fungi. We added 13C-labeled alanine to the soil surrounding one sporocarp within each pair; the second served as an unlabeled control. Peak rates of 13C-respiration from alanine were higher in the labeled sporocarp plots than the controls, indicating that the 13C-alanine was detectably respired from the soil. “Reference” plots adjacent to the sporocarps served as an indication of background 13C-respiration rates released by the soil community as a whole. Ectomycorrhizal sporocarps displayed higher 13C-respiration rates than their reference plots. Thus, the sporocarps and associated mycorrhizal mycelium appeared to contribute significantly to the release of alanine-derived 13CO 2, confirming the hypothesis that ectomycorrhizal fungi may access soil amino acid pools under natural conditions.

Effects of Organic Enrichment of Mine Spoil on Growth and Nutrient Uptake in Oak Seedlings Inoculated with Selected Ectomycorrhizal Fungi

Abstract Poor growth of Quercus robur L. (oak) trees has been reported on mine sites where overburden and subsoil have been used in the reinstatement of surface layers. This stunting has been attributed to a lack of macronutrients and to an adverse soil environment for root growth and mycorrhizal development. Growth, mineral nutrition, and ectomycorrhizal colonization of Q. robur seedlings were studied in an experiment carried out under controlled growing conditions in which mine spoil material was enriched with a leaf litter mulch. Enrichment of mine spoil material was found to produce a significant increase in growth and foliar N concentrations of oak seedlings. Inoculation with three taxa of ectomycorrhizal fungi did not benefit seedlings when mine spoil was the only substrate, possibly due to the poor physical properties of the unamended spoil and lack of nutrients. Inoculation with two taxa, Laccaria laccata and Hebeloma crustuliniforme, isolated from 3-year-old trees produced a significant stimulation of growth in the organically enriched treatment, which was believed to be due to greater uptake of mineralized N. However, Cortinarius anomalus isolated from fruit bodies associated with a 15-year-old tree did not increase biomass. The presence of organic matter was found to result in a significant stimulation of mycorrhizal infection by both inoculum and contaminant mycobionts. Recommendations are made for improving the establishment and growth of oak seedlings on reinstated sites.

Reciprocal interactions between Scots pine and soil food web structure in the presence and absence of ectomycorrhiza.

Mycorrhizal plants are commonly believed to direct much more of their photosynthates into the soil than non-mycorrhizal plants. As the growth of most organisms of the detrital food web is limited by energy, the flow of C through mycorrhizal plants into the below-ground milieu is widely assumed to nourish a variety of decomposer organisms in soils. In the current experiment, I explored whether some representatives of soil mesofauna, either fungivores or microbi-detritivores, derive benefit from the presence of ectomycorrhizal (EM) fungi growing on the roots of Scots pine (Pinus sylvestris). I also investigated whether the role of soil mesofauna in affecting pine growth depends on the presence of EM fungi in the pine rhizosphere. The study was established in microcosms with a mixture of raw humus and sand. 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 four taxa of EM fungi, were planted in the microcosms. Five treatments with different food web configurations were established: (1) saprophytic microbes alone, (2) as (1) but with the omnivorous enchytraeid species Cognettia sphagnetorum present, (3) as (1) but with Collembola (Hypogastrura assimilis), (4) as (1) but with four species of oribatid mites (Acari) involved, and (5) as 1) but with C. sphagnetorum, H. assimilis and the Acari. The microcosms were incubated in a climate chamber with varying temperature and illumination regimes for two growing periods for the pine. After 60 weeks, pine biomass production was significantly greater in the mycorrhizal systems, the total biomass being 1.43 times higher in the presence than absence of EM fungi. Similarly, almost ten times more fungal biomass was detected on pine roots growing in the mycorrhizal than in the non-mycorrhizal systems. The presence of EM fungi was also associated with significantly lowered pH and percent organic matter of the soil. Despite the clearly larger biomass of both the pines and the fungi on the pine roots, neither the numbers nor biomasses of the mesofauna differed significantly between the EM and non-EM systems. The presence of Collembola and C. sphagnetorum had a positive influence on pine growth, particularly in the absence of EM fungi, whereas oribatid mites had no effects on pine growth. The complexity of the mesofaunal community was not related to the biomass production of the pines in a straightforward manner; for example, the complex systems with each faunal group present did not produce more pine biomass than the simple systems where C. sphagnetorum existed alone. The results of this experiment suggest that the short-term role of EM fungi in fuelling the detrital food web is less significant than generally considered, but that their role as active decomposers and/or stimulators of the activity of saprophytic microbes can be more important than is often believed.

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.

Growth of Birch and Pine Seedlings in Relation to Grazing by Soil Fauna on Ectomycorrhizal Fungi

It is hypothesized that mutualistic relationships can be persistent due to a third “external” species constraining the otherwise unlimited growth of the mutualists. By consuming mycorrhizal fungi, soil fauna may exert such a control over the development of the plant—fungus symbiosis. In this study I investigated the influence of soil fauna on the mutualistic association of ectomycorrhizal (EM) fungi and seedlings of birch and pine in transparent experimental microcosms simulating coniferous forest soil. The soil was defaunated, reinoculated with soil microbes, and seedlings of silver birch (Betula pendula) or Scots pine (Pinus sylvestris) infected with 3—4 taxa of EM fungi were separately planted in the microcosms. Half of the microcosms were thereafter reinoculated with diverse soil fauna. Microcosms were incubated in a climate chamber with varying illumination and temperature regimes for two annual cycle of the plant. After 57 wk the biomass of EM fungi was significantly reduced in the refaunated microcosms, the amount of fungi on birch and pine roots being 50 and 20%, respectively, of that in the non—refaunated controls. Similarly, the total microbial biomass in the bulk soil was significantly lower in the refaunated systems. The shoot production of both tree species was significantly enhanced in the presence of fauna: by the end of the experiment 1.5 (birch) and 1.7 (pine) times more aboveground biomass was produced in the refaunated microcosms than in the controls. Concentrations of N and P in the foliage of both tree species were also higher in the refaunated microcosms. These data indicate that the obvious reduction in EM fungi due to soil fauna is not harmful for the plant—fungus symbiosis provided that the community composition of the belowground food web is complex enough to ensure efficient mobilization of nutrients in the mycorrhizosphere.