Mycorrhizal colonization mediated by species interactions in arctic tundra

The Alaskan tussock tundra is a strongly nutrient-limited ecosystem, where almost all vascular plant species are mycorrhizal. We established a long-term removal experiment to document effects of arctic plant species on ecto- and ericoid mycorrhizal fungi and to investigate whether species interactions and/or nutrient availability affect mycorrhizal colonization. The treatments applied were removal of Betula nana (Betulaceae, dominant deciduous shrub species), removal of Ledum palustre (Ericaceae, dominant evergreen shrub species), control (no removal), and each of these three treatments with the addition of fertilizer. After 3 years of Ledum removal and fertilization, we found that overall ectomycorrhizal colonization in Betula was significantly reduced. Changes in ectomycorrhizal morphotype composition in removal and fertilized treatments were also observed. These results suggest that the effect of Ledum on Betula 's mycorrhizal roots is due to sequestration of nutrients by Ledum, leading to reduced nutrient availability in the soil. In contrast, ericoid mycorrhizal colonization was not affected by fertilization, but the removal of Betula and to a lower degree of Ledum resulted in a reduction of ericoid mycorrhizal colonization suggesting a direct effect of these species on ericoid mycorrhizal colonization. Nutrient availability was only higher in fertilized treatments, but caution should be taken with the interpretation of these data as soil microbes may effectively compete with the ion exchange resins for the nutrients released by plant removal in these nutrient-limited soils.     

Does the sequence of plant dominants affect mycorrhiza development in simulated succession on spoil banks?

The aim of this field study was to examine how the development of arbuscular mycorrhizal fungi (AMF) on coal mine spoil banks is affected by the presence of plants with different mycorrhizal status. A 3-year trial was conducted on the freshly created spoil bank Vršany, North-Bohemian coal basin, the Czech Republic. Three plant species – non-mycotrophic annual Atriplex sagittata, highly mycotrophic annual Tripleurospermum inodorum (both dominants of early stages of succession) and facultatively mycotrophic Arrhenatherum elatius (a perennial grass species of the later stage of succession) – were planted on 1 m² plots over 3 years in different sequences that simulated the progress of succession on spoil banks. The development of AMF populations was monitored by evaluation of mycorrhizal colonization of plant roots and by measurement of the mycorrhizal inoculation potential (MIP) of soil. These two parameters were compared between plots inoculated with the mixture of three AMF isolates – Glomus mosseae BEG95, G. claroideum BEG96 and G. intraradices BEG140 – (“inoculated plots”) and plots exposed only to natural dispersal of AMF propagules (“uninoculated plots”). Highly colonized roots of plants together with a high MIP of soil in uninoculated plots were already found at the end of the first season, indicating rapid natural dispersal of AMF propagules. Root colonization of facultatively mycotrophic and non-mycotrophic plants in later years was affected by the mycorrhizal status of the previous plant species. The MIP of soil continuously increased throughout the experiment; in uninoculated plots, the MIP was temporarily decreased if plant species of higher mycotrophy were replaced by species of lower mycotrophy. The results lead to the conclusion that AMF colonize freshly formed sites very quickly and reproduce or accumulate in the soil, which leads to increasing MIP values. However, this infective potential can be decreased if non-mycotrophic plants predominate on the site.     

Utilisation of organic nitrogen and phosphorus sources by mycorrhizal endophytes of Woollsia pungens (Cav.) F. Muell. (Epacridaceae)

 The ability of four ericoid mycorrhizal endophytes isolated from roots of Woollsia pungens (Cav.) F. Muell. (Epacridaceae) to utilise organic forms of nitrogen and phosphorus during growth in axenic culture was assessed. All isolates were able to utilise glutamine, arginine and bovine serum albumin (BSA), along with NH₄ ⁺ or NO₃ ^–, in most cases yielding at least as much biomass as the ericoid mycorrhizal endophyte Hymenoscyphus ericae (Read) Korf & Kernan. All isolated endophytes were able to utilise BSA, arginine and glutamine as sole sources of N and C. With the exception of a single isolate (C40), which showed little growth on glutamine, biomass yields on glutamine as the sole N and C source was significantly greater for all isolates than on either of the other two organic N sources. Two isolates from W. pungens (C40 and A43) utilised DNA and sodium inositol hexaphosphate as sole P sources, in each case yielding significantly more biomass than H. ericae. The results suggest that mycorrhizal endophytes from epacrid plant hosts and those from ericaceous hosts have similar abilities to utilise organic forms of N and P. Accepted: 4 September 1998     

Fungal associations of Danish Calluna vulgaris roots with special reference to ericoid mycorrhiza

Fungi were isolated from young, serial-washed roots of Calluna sampled from a Danish heathland, Hjelm Hede. Of the 626 isolates, those that were dark, sterile and septate were divided into 13 morphological groups based on their appearance in culture on malt agar. Mycorrhizal synthesis in vitro showed that several groups formed typical ericoid mycorrhiza with seedlings of Calluna; these ericoid mycorrhizal fungi were morphologically similar to Hymenoscyphus ericae. The identities of the other dark, septate fungi are uncertain. Oidiodendron spp. were isolated in a very low frequency; these fungi also formed typical ericoid mycorrhiza. The Calluna root system on Hjelm Hede demonstrated a high morphological diversity among the associated dark, septate fungi suggesting that more than one fungus could coexist in the same host root system.     

Suppression of ectomycorrhizae on canopy tree seedlings in Rhododendron maximum L. (Ericaceae) thickets in the southern Appalachians

 Thickets of Rhododendron maximum (Ericaceae) (Rm) in the southern Appalachians severely limit regeneration of hardwood and coniferous seedlings. Experimental blocks were established in and out of Rm thickets in a mature, mixed hardwood/conifer forest in Macon County, N.C. Litter and organic layer substrates were removed, composited and redistributed among plots within the blocks (except for control plots). Seedlings of northern red oak (Quercus rubra) and eastern hemlock (Tsuga canadensis) were planted in the plots and harvested at the end of the first and second growing seasons. Litter manipulation had no effect on total mycorrhizal colonization, but the distribution of Cenococcum geophilum mycorrhizae was altered. After the first year, percent mycorrhizal colonization of hemlocks not in Rm thickets (62%) was at least three times higher than in Rm thickets (19%), and the ramification index (no. of mycorrhizae cm^–1) had increased by more than a factor of four (2.83 versus 0.61). In addition, colonization of 1-year-old hemlocks by C. geophilum was significantly higher within blocks with (10.4%) than without (4.6%) Rm. Differences in mycorrhizal colonization, ramification indices and colonization by C. geophilum were absent or less pronounced on 2-year-old hemlocks and 1- and 2-year-old oak seedlings. The biomasses of first year oak roots and shoots and second year shoots were 50% less in Rm thickets. Biomasses of first year hemlock roots and second year shoots were also reduced. Mycorrhizal parameters were correlated with some growth parameters only for hemlock seedlings, but did not explain most of the variation observed. Accepted: 12 February 1999     

Effects of ectomycorrhizal colonization and nitrogen fertilization on morphology of root tips in a <Emphasis Type="Italic">Larix gmelinii</Emphasis> plantation in northeastern China

Root morphology is important in understanding root functions in forest ecosystems. However, the effects of ectomycorrhizal colonization and soil nutrient availability on root morphology is not clear. In this study, root morphology in relation to season, soil depth, soil nitrogen (N) availability, and mycorrhizal fungal colonization were investigated in a larch (Larix gmelinii) plantation in northeastern China. The first-order roots (or root tips) of larch were sampled four times in May, July, and September of 2005, and May of 2006 from two depths of upper soil layer (0–10 and 10–20 cm) in the control and the N-fertilized plots. The results showed that ectomycorrhizal (ECM) colonization rates for the first-order roots were reduced by 17% under N fertilization. The peak of root colonization rates occurred in summer and was positively correlated with soil temperature. ECM colonization significantly altered root morphology: root diameter was increased by 19 and 29%, root length shortened by 27 and 25%, and specific root length (SRL) reduced by 16 and 19% for the control and the N-fertilized plots, respectively. N fertilization led to decreased root length, but did not affect root diameter and SRL. In addition, effects of ECM colonization on root morphology varied with season and soil depth. The observed relationships among ECM fungal colonization, soil N availability, and root-tip morphology should improve our understanding of how root tips respond to environmental changes in soil in temperate forest ecosystems.     

Correlations between foliar δ15N and nitrogen concentrations may indicate plant-mycorrhizal interactions

Nitrogen isotope measurements may provide insights into changing interactions among plants, mycorrhizal fungi, and soil processes across environmental gradients. Here, we report changes in δ¹⁵N signatures due to shifts in species composition and nitrogen (N) dynamics. These changes were assessed by measuring fine root biomass, net N mineralization, and N concentrations and δ¹⁵N of foliage, fine roots, soil, and mineral N across six sites representing different post-deglaciation ages at Glacier Bay, Alaska. Foliar δ¹⁵N varied widely, between 0 and –2‰ for nitrogen-fixing species, between 0 and –7‰ for deciduous non-fixing species, and between 0 and –11‰ for coniferous species. Relatively constant δ¹⁵N values for ammonium and generally low levels of soil nitrate suggested that differences in ammonium or nitrate use were not important influences on plant δ¹⁵N differences among species at individual sites. In fact, the largest variation among plant δ¹⁵N values were observed at the youngest and oldest sites, where soil nitrate concentrations were low. Low mineral N concentrations and low N mineralization at these sites indicated low N availability. The most plausible mechanism to explain low δ¹⁵N values in plant foliage was a large isotopic fractionation during transfer of nitrogen from mycorrhizal fungi to plants. Except for N-fixing plants, the foliar δ¹⁵N signatures of individual species were generally lower at sites of low N availability, suggesting either an increased fraction of N obtained from mycorrhizal uptake (f), or a reduced proportion of mycorrhizal N transferred to vegetation (T _r). Foliar and fine root nitrogen concentrations were also lower at these sites. Foliar N concentrations were significantly correlated with δ¹⁵N in foliage of Populus, Salix, Picea, and Tsuga heterophylla, and also in fine roots. The correlation between δ¹⁵N and N concentration may reflect strong underlying relationships among N availability, the relative allocation of carbon to mycorrhizal fungi, and shifts in either f or T _r. Received: 14 December 1998 / Accepted: 16 August 1999     

Diversity of ericoid mycorrhizal fungi isolated from hair roots of Rhododendron obtusum var. kaempferi in a Japanese red pine forest

 The diversity of ericoid mycorrhizal fungi of Rhododendron obtusum var. kaempferi was examined in a stand of Pinus densiflora at Tsukuba, Japan. In total, 153 slow-growing fungal isolates were obtained from roots of R. obtusum var. kaempferi, in which 113 isolates formed an ericoid mycorrhizal structure in vitro. Among them, 53 isolates were morphologically identified as Oidiodendron maius, but the others were not identified due to their sterilities. PCR-RFLP analysis in the rDNA-ITS region divided them into four different RFLP types. Phylogenetic analysis from sequence data of the region suggested that the four RFLP types belonging to distinct taxa and one sterile type are considered to be Hymenoscyphus ericae. This study is the first report of ericoid mycorrhizal fungi in a natural habitat in Japan. Received: August 23, 2002 / Accepted: December 11, 2002 Acknowledgments We thank Dr. K. Narisawa, Plant Biotechnology Institute, Ibaraki Agricultural Center, and Dr. R.S. Currah, Department of Biological Science, University of Alberta, for their helpful advice. Contribution no. 176, Laboratory of Plant Parasitic Mycology, Institute of Agriculture and Forestry, University of Tsukuba, Japan Correspondence to:M. Kakishima     

Foliar and fungal <Superscript>15</Superscript> N:<Superscript>14</Superscript> N ratios reflect development of mycorrhizae and nitrogen supply during primary succession: testing analytical models

Nitrogen isotopes (¹⁵N/¹⁴N ratios, expressed as δ¹⁵N values) are useful markers of the mycorrhizal role in plant nitrogen supply because discrimination against ¹⁵N during creation of transfer compounds within mycorrhizal fungi decreases the ¹⁵N/¹⁴N in plants (low δ¹⁵N) and increases the ¹⁵N/¹⁴N of the fungi (high δ¹⁵N). Analytical models of ¹⁵N distribution would be helpful in interpreting δ¹⁵N patterns in fungi and plants. To compare different analytical models, we measured nitrogen isotope patterns in soils, saprotrophic fungi, ectomycorrhizal fungi, and plants with different mycorrhizal habits on a glacier foreland exposed during the last 100 years of glacial retreat and on adjacent non-glaciated terrain. Since plants during early primary succession may have only limited access to propagules of mycorrhizal fungi, we hypothesized that mycorrhizal plants would initially be similar to nonmycorrhizal plants in δ¹⁵N and then decrease, if mycorrhizal colonization were an important factor influencing plant δ¹⁵N. As hypothesized, plants with different mycorrhizal habits initially showed similar δ¹⁵N values (−4 to −6‰ relative to the standard of atmospheric N₂ at 0‰), corresponding to low mycorrhizal colonization in all plant species and an absence of ectomycorrhizal sporocarps. In later successional stages where ectomycorrhizal sporocarps were present, most ectomycorrhizal and ericoid mycorrhizal plants declined by 5–6‰ in δ¹⁵N, suggesting transfer of ¹⁵N-depleted N from fungi to plants. The values recorded (−8 to −11‰) are among the lowest yet observed in vascular plants. In contrast, the δ¹⁵N of nonmycorrhizal plants and arbuscular mycorrhizal plants declined only slightly or not at all. On the forefront, most ectomycorrhizal and saprotrophic fungi were similar in δ¹⁵N (−1 to −3‰), but the host-specific ectomycorrhizal fungus Cortinarius tenebricus had values of up to 7‰. Plants, fungi and soil were at least 4‰ higher in δ¹⁵N from the mature site than in recently exposed sites. On both the forefront and the mature site, host-specific ectomycorrhizal fungi had higher δ¹⁵N values than ectomycorrhizal fungi with a broad host range. From these isotopic patterns, we conclude:(1) large enrichments in ¹⁵N of many ectomycorrhizal fungi relative to co-occurring ectomycorrhizal plants are best explained by treating the plant-fungal-soil system as a closed system with a discrimination against ¹⁵N of 8–10‰ during transfer from fungi to plants, (2) based on models of ¹⁵N mass balance, ericoid and ectomycorrhizal fungi retain up to two-thirds of the N in the plant-mycorrhizal system under the N-limited conditions at forefront sites, (3) sporocarps are probably enriched in ¹⁵N by an additional 3‰ relative to available nitrogen, and (4) host-specific ectomycorrhizal fungi may transfer more N to plant hosts than non-host-specific ectomycorrhizal fungi. Our study confirms that nitrogen isotopes are a powerful tool for probing nitrogen dynamics between mycorrhizal fungi and associated plants.     

Influence of arbuscular mycorrhiza on clover and ryegrass grown together in a soil spiked with polycyclic aromatic hydrocarbons

 The effect of arbuscular mycorrhiza (AM) on white clover and ryegrass grown together in a soil spiked with polycyclic aromatic hydrocarbons (PAH) was assessed in a pot experiment. The soil was spiked with 500 mg kg^–1 anthracene, 500 mg kg^–1 chrysene and 50 mg kg^–1 dibenz(a,h)anthracene, representing common PAH compounds with three, four and five aromatic rings, respectively. Three treatments and two harvest times (8 and 16 weeks) were imposed on plants grown in spiked soil: no mycorrhizal inoculation, mycorrhizal inoculation (Glomus mosseae P2, BEG 69) and mycorrhizal inoculation and surfactant addition (Triton X-100). Pots without PAH were also included as a control of plant growth and mycorrhizal colonization as affected by PAH additions. The competitive ability of clover vis-à-vis ryegrass regarding shoot and root growth was enhanced by AM, but reduced by PAH and the added surfactant. This was reflected by mycorrhizal root colonization which was moderate for clover (20–40% of total root length) and very low for ryegrass (0.5–5% of total root length). Colonization of either plant was similar in spiked soil with and without the added surfactant, but the PAH reduced colonization of clover to half that in non-spiked soil. P uptake was maintained in mycorrhizal clover when PAH were added, but was reduced in non-mycorrhizal clover and in mycorrhizal clover that received surfactant. Similar effects were not observed on ryegrass. These results are discussed in the context of the natural attenuation of organic pollutants in soils. Accepted: 12 June 2000     

Mutualistic functioning of indigenous arbuscular mycorrhizae in spring barley and winter wheat after cessation of long-term phosphate fertilization

 The influence of 23 years of phosphorus (P) application at three annual rates of 0, 17.5 and 52.5 kg ha^–1 on arbuscular mycorrhizal (AM) fungal colonization was studied 10 years after the fertilization treatment ended. The annual application of 52.5 kg ha^–1 was about twice the annual crop P extraction and after 23 years had resulted in a measured increase of 23% in the soil total-P concentration. After 10 and 11 years without fertilization, the total mycorrhizal and arbuscular colonization of the plots previously fertilized at this high rate were still significantly lower than in the plots subjected to the 0 and 17.5 kg ha^–1 rates. Plots previously fertilized annually at the rate of 52.5 kg ha^–1 also had a lower benefit : cost ratio for the symbiosis between AM fungi and plants. Furthermore, P-use efficiency was lower in these plots, although no decrease in total dry matter production was found. Accepted: 13 October 2000     

Influence of edaphic and climatic factors on dynamics of root colonization and spore density of vesicular-arbuscular mycorrhizal fungi in Acacia farnesiana Willd. and A. planifrons W.et.A.

 A study was conducted to assess the dynamics of vesicular-arbuscular mycorrhizal (VAM) fungi associated with Acacia farnesiana and A. planifrons in moderately fertile alkaline soils. The intensity of root colonization by VAM fungi and the distribution of VAM fungal structures varied with host species over a period of time. The occurrence of vesicles with varied morphology in the mycorrhizal roots indicates infection by different VAM fungal species. This was further confirmed from the presence of spores belonging to different VAM fungal species in the rhizosphere soils. Root colonization and spore number ranged from 56% – 72% and 5 – 14 g^{–  1}soil in A. farnesiana and from 60% – 73% and 5 – 15 g^{–  1} soil in A. planifrons. Per cent root colonization and VAM spore number in the rhizosphere soil were inversely related to each other in both the Acacia species. However, patterns of the occurrence of VAM fungal structures were erratic. Spores of Acaulospora foveata, Gigaspora albida, Glomus fasciculatum, G. geosporum and Sclerocystis sinuosa were isolated from the rhizosphere of A. farnesiana whereas A. scrobiculata, G. pustulatum, G. fasciculatum, G. geosporum and G. microcarpum were isolated from that of A. planifrons. The response of VAM status to fluctuating edaphic factors varied with host species. In A. farnesiana though soil nitrogen (N) was positively correlated with root colonization, soil moisture, potassium and air temperature were negatively correlated to both root colonization and spore number. Per cent root colonization and spore number in A. planifrons were negatively related to each other. Further, in A. planifrons as the soil phosphorus and N were negatively correlated with the density of VAM fungal spores, the same edaphic factors along with soil moisture negatively influenced root colonization. Received: 16 May 1995 / Accepted: 7 February 1996     

Diversity of root-associated fungal endophytes in Rhododendron fortunei in subtropical forests of China

To investigate the diversity of root endophytes in Rhododendron fortunei, fungal strains were isolated from the hair roots of plants from four habitats in subtropical forests of China. In total, 220 slow-growing fungal isolates were isolated from the hair roots of R. fortunei. The isolates were initially grouped into 17 types based on the results of internal transcribed spacer-restriction fragment length polymorphism (ITS-RFLP) analysis. ITS sequences were obtained for representative isolates from each RFLP type and compared phylogenetically with known sequences of ericoid mycorrhizal endophytes and selected ascomycetes or basidiomycetes. Based on phylogenetic analysis of the ITS sequences in GenBank, 15 RFLP types were confirmed as ascomycetes, and two as basidiomycetes; nine of these were shown to be ericoid mycorrhizal endophytes in experimental cultures. The only common endophytes of R. fortunei were identified as Oidiodendron maius at four sites, although the isolation frequency (3–65%) differed sharply according to habitat. Phialocephala fortinii strains were isolated most abundantly from two habitats which related to the more acidic soil and pine mixed forests. A number of less common mycorrhizal RFLP types were isolated from R. fortunei at three, two, or one of the sites. Most of these appeared to have strong affinities for some unidentified root endophytes from Ericaceae hosts in Australian forests. We concluded that the endophyte population isolated from R. fortunei is composed mainly of ascomycete, as well as a few basidiomycete strains. In addition, one basidiomycete strain was confirmed as a putative ericoid mycorrhizal fungus.     

Effects of AM colonization on “wild tobacco” plants grown in zinc-contaminated soil

This greenhouse study aimed to determine the effect of colonization by the arbuscular mycorrhizal (AM) fungus (Glomus intraradices Schenck & Smith) on the “wild” tobacco (Nicotiana rustica L. var. Azteca), under soil–zinc (Zn) conditions. Plants of N. rustica were grown in AM or non-AM inoculated substrate and subjected to four soil–[Zn] concentrations (0, 50, 100, and 250 mg Zn kg⁻¹ dry soil). The AM root colonization increased markedly from 14 to 81% with the increasing soil–[Zn] and the mycorrhizal structures were significantly more abundant at the highest soil–[Zn], suggesting that Zn may be involved directly or indirectly in AM root colonization. In addition, total Zn content or Zn concentrations in shoots and roots were shown to increase as soil–[Zn] increased in both AM and non-AM plants. As for the growth parameters studied, there were no significant differences between treatments despite the increase in Zn content or concentration. The AM roots subjected to the highest soil–[Zn] had a significant reduction by about 50% of total Zn content and Zn concentration compared to non-AM roots. Still, the relative extracted Zn percentage decreased dramatically as soil–[Zn] increased. Soil pH was significantly lower in non-AM than AM treatments at the highest soil–[Zn]. In summary, AM plants (particularly roots) showed lower Zn content and concentration than non-AM plants. In this regard, the AM fungi have a protective role for the host plant, thus playing an important role in soil-contaminant immobilization processes; and, therefore, are of value in phytoremediation, especially when heavy metals approach toxic levels in the soil.     

Formation of structures resembling ericoid mycorrhizas by the root endophytic fungus Heteroconium chaetospira within roots of Rhododendron obtusum var. kaempferi

A resynthesis study was conducted to clarify the relationship between the root endophyte, Heteroconium chaetospira and the ericaceous plant, Rhododendron obtusum var. kaempferi. The host plant roots were recovered 2 months after inoculation, and the infection process and colonization pattern of the fungus were observed under a microscope. The hyphae of H. chaetospira developed structures resembling ericoid mycorrhizas, such as hyphal coils within the host epidermal cells. These structures were morphologically the same as previously reported ericoid mycorrhizal structures. The frequencies of hyphal coils within the epidermal cells of host roots ranged from 13 to 20%. H. chaetospira did not promote or reduce host plant growth. This is the first reported study that H. chaetospira is able to form structures resembling mycorrhizas within the roots of ericaceous plants.     

Ericoid mycorrhizal association: ability to adapt to a broad range of habitats

Ericoid mycorrhizal fungi are symbiotically associated with the roots of members of the Ericaceae which include genera such as Calluna, Epacris, Erica, Rhododendron and Vaccinium. These ericoid mycorrhizal associations have adapted to a broad range of habitats, from mor humus soils of the northern hemisphere to sandy soils occurring in the southern hemisphere. They also play an important part in enabling plants like Calluna vulgaris (L.) Hull in the northern hemisphere to colonize mine spoils which are inhospitable environments of toxic waste for growth of most plants. The mechanisms of utilizing complex forms of nitrogen and phosphorus and providing protection against toxic metals are described. These mechanisms carried out by ericoid mycorrhizal associations enable host plants to establish in diverse habitats.     

The mycorrhiza of <Emphasis Type="Italic">Schizocodon soldanelloides</Emphasis> var. <Emphasis Type="Italic">magnus</Emphasis> (Diapensiaceae) is regarded as ericoid mycorrhiza from its structure and fungal identities

Structure and fungal identities were examined in the mycorrhizal roots of Schizocodon soldanelloides var. magnus (Diapensiaceae) to determine the mycorrhizal category. Previous studies had suggested the mycorrhizae of Diapensiaceae could be categorized as ericoid, but the mycorrhizal fungi have never been identified. The diameter of the fine lateral roots, in which coiled hyphae were found in epidermal cells, was mostly less than 100 μm. Molecular analyses identified the fungal isolates to be Helotiales and Oidiodendron. From the structure and fungal identities, we confirmed that the mycorrhiza of S. soldanelloides is an ericoid mycorrhiza.     

Distribution of different mycorrhizal classes on Mount Koma, northern Japan

To investigate the role of mycorrhizae in nutrient-poor primary successional volcanic ecosystems, we surveyed mycorrhizal frequencies on the volcano Mount Koma (42°04N, 140°42E, 1,140 m elevation) in northern Japan. After the 1929 eruptions, plant community development started at the base of the volcano. Ammonia and nitrate levels, along with plant cover, decreased with increasing elevation, whereas phosphorus did not. In total, 305 individuals of 56 seed plant species were investigated in three elevational zones (550–600 m, 650–700 m, and 750–800 m). Five mycorrhizal classes were classified based on morphological traits: ecto- (ECM), arbuscular (AM), arbutoid, ericoid, and orchid mycorrhiza. All plant species were mycorrhizal to at least some extent, with most widespread tree species being heavily ectomycorrhizal. In addition, of 16 tree species collected in all three zones, 6 differed in the frequencies of ECM on roots between elevational zones, and 3 of these 6 species increased in frequency with increasing elevation. These results suggest that ECM colonization in some tree species is related to establishment in nutrient-poor habitats. All species of Ericaceae and Pyrolaceae had ericoid mycorrhizae, and an Orchidaceae species had orchid mycorrhizae. Herbaceous species, except for the low mycorrhizal frequency of Carex oxyandra and two Polygonaceae species, and ericoid and orchid mycorrhizal species, were generally AM. Of herbaceous species, Anaphalis margaritacea var. angustior increased AM frequency and decreased ECM frequency with increasing elevation, and Hieracium umbellatum increased ECM frequency. In total, the establishment of herbaceous species was not sufficiently explained by AM colonization on roots. Tree individuals developed 2–3 classes of mycorrhizae more than herbs at each elevational zone. We conclude that the symbiosis between seed plants and mycorrhizae, ECM in particular, greatly influences plant community structures on Mount Koma. Not only a single mycorrhizal class, but combinations of mycorrhizal classes should be studied to clarify effects on plant community dynamics.     

Occurrence of carpophores of ectomycorrhizal fungi in selected stands ofPinus sylvestris in the Netherlands in relation to stand vitality and air pollution

The relation between the occurrence of carpophores of mycorrhizal fungi, tree vitality, and air pollution in ‘young’ (5–10 years) and ‘old’ (50–80 years) stands ofPinus sylvestris L. was investigated. In the Netherlands 21 homogeneous plots of 1000 m² were selected on dry, sandy soils. Tree vitality was assessed in the summer of 1985 and during the autumn the plots were searched for carpophores of mycorrhizal fungi. In the young plots 3 times more species of ectomycorrhizal fungi and 20 times more carpophores per plot were found than in the old plots. In the old plots, the number of carpophores and the number of species showed significant positive correlations with the average number of needleyears of the trees. The number of carpophores and the number of species were significantly negative correlated with the concentrations of SO₂ and O₃ in the air and the amount of NH₃ emission. The number of needleyears, the crown density and the overall tree vitality were found to be significantly negative correlated with the amount of NH₃ emission, and the number of needleyears also with the concentration of O₃ in the air. Such correlations were not found for the young plots. No differences were found in soil chemical properties between the plots. Evidence was obtained that the fructification of mycorrhizal fungi of old stands ofPinus sylvestris is influenced by air pollution either directly, or indirectly by way of tree vitality. It is hypothesized that the young plots offer more advantageous circumstances for fructification of the fungi because of the disturbance of the upper soil-layer at the time of planting.     

Can NPK fertilizers enhance seedling growth and mycorrhizal status of Tuber melanosporum-inoculated Quercus ilex seedlings?

Although successful cultivation of the black truffle (Tuber melanosporum) has inspired the establishment of widespread truffle orchards in agricultural lands throughout the world, there are many unknowns involved in proper management of orchards during the 6–10 years prior to truffle production, and there are conflicting results reported for fertilizer treatments. Here, we systematically evaluate the combined effects of nitrogen, phosphorous, and potassium with different doses of each element, applied to either foliage or roots, on plant growth parameters and the mycorrhizal status of outplanted 3-year-old seedlings in five experimental Quercus ilex–T. melanosporum orchards. Fertilization did not significantly improve seedling aboveground growth, but the plants treated with the fertilizer 12-7-7 applied to the roots (HNr) displayed longer field-developed roots. Only the fertilizer with the highest dose of K (10-6-28) applied to the foliage (HKf) increased the probability of fine root tip colonization by T. melanosporum in field-developed roots. However, the plants treated with the same fertilizer applied to the soil (HKr) presented the highest probability for colonization by other competing mycorrhizal soil fungi. Potassium seems to have an important role in mycorrhizal development in these soils. Apart from T. melanosporum, we found 14 ectomycorrhizal morphotypes, from which seven were identified to species level, three to genus, two to family, and two remained unidentified by their morphological characteristics and DNA analyses.