Early colonization of red alder and Douglas fir by ectomycorrhizal fungi and Frankia in soils from the Oregon coast range

The potential for mycorrhizal formation and Frankia nodulation were studied in soils from six sites in the Pacific Northwest. The sites included young and old alder stands, a 1-year-old conifer clear-cut, a young conifer plantation, and rotation-aged and old-growth conifer stands. A bioassay procedure was used with both red alder and Douglas fir seedlings as hosts. After 6 weeks growth, seedlings of both hosts were harvested every 3 weeks for 21 weeks and numbers of nodules and ectomycorrhizal types estimated. Nodules formed on red alder and ectomycorrhizae formed on both alder and Douglas fir in soil from all sites. Nodulation potential was highest in soil from the alder stands and the conifer plantation. Seven morphologically distinct ectomycorrhizal types were recovered on Douglas fir and five on alder. Only Thelephora terrestris, a broad-host-range mycobiont, formed mycorrhizae on both hosts. New ectomycorrhizal types formed on both hosts throughout the bioassay. Ectomycorrhizal colonization of alder was greatest in the alder and clear-cut soils. Low ectomycorrhizal colonization on alder was found in soils from sites where conifers were actively growing. Ectomycorrhizal colonization of Douglas fir was highest in the young alder and conifer plantation soils and was low in the rotation-aged conifer soil. The highest diversity of ectomycorrhizal types was found on alder in the conifer clear-cut soil and on Douglas fir in the rotation-aged conifer soil. Effects of host specificity, nodulation and mycorrhiza-forming potential and nodule-mycorrhiza interactions on seedling establishment are discussed in relation to seral stage dynamics and attributes of pioneer ectomycorrhizal fungal species.     

Response of ectomycorrhizalPinus banksiana andPicea glauca to heavy metals in soil

Pinus banksiana andPicea glauca inoculated or not with the ectomycorrhizal fungusSuillus luteus were grown in a sandy loam soil containing a range of Cd, Cu, Ni, Pb and Zn concentrations. Ectomycorrhizal colonization rates were significantly reduced on Pinus and Picea seedlings by the heavy metals, particularly Cd and Ni. Needle tissue metal concentrations were lower in ectomycorrhizal seedlings at low soil metal concentrations. However, at higher soil concentrations, heavy metal concentrations of needle tissue were similar in ectomycorrhizal and nonmycorrhizal plants. The growth of nonmycorrhizal seedlings exposed to heavy metals was reduced compared to those inoculated withSuillus luteus. Apparently ectomycorrhizal colonization can protect Pinus and Picea seedlings from heavy metal toxicity at low or intermediate soil concentrations of Cd, Cu, Ni, Pb and Zn.     

Mycorrhizal colonization status of plant species established in an exposed area following the 2000 eruption of Mt. Usu, Hokkaido, Japan

We investigated the ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) colonization status of plant seedlings that established in areas devastated by the eruption in March 2000 of Mt. Usu, Hokkaido, Japan. In 2005, we estimated the mycorrhizal colonization ratios and frequencies in seedlings of twelve herbaceous and seven woody plant species. Although arbuscular mycorrhizas were found to colonize Equisetum arvense and Polygonum sachalinense, they were presented at very low frequencies and colonization ratios. Other herbaceous plants exhibited higher frequencies of AM associations and either AM and/or ECM fungal associations were observed in all of the woody plant seedlings investigated. The dominant woody plant species (Populus maximowiczii, Salix sachalinensis and Salix hultenii var. angustifolia) associated mainly with ECM fungi and exhibited variable associations with AM fungi. Mycorrhizal associations were common and significant events for plant establishment, even in the early stages of the revegetation process.     

Growth,root colonization and nutrient status of Helianthemum sessiliflorum Desf. inoculated with a desert truffle Terfezia boudieri Chatin

This study aims to investigate the effects of inoculation using Terfezia boudieri Chatin ascospores (ectomycorrhizal fungus) on growth, root colonization and nutrient status of Helianthemum sessiliflorum Desf. seedlings grown in pots on two-soil types (gypseous and sandy loam). Mycorrhizal seedlings had significantly increased their height and leaf number compared to non-mycorrhizal ones. Regardless of mycorrhizal inoculation treatments, the plants growing on gypseous soil showed higher growth as compared to sandy loam one. It appears that inoculation with T. boudieri changed root morphology, increasing branching of first-order lateral roots of H. sessiliflorum seedlings. The highest root mycorrhizal colonization was recorded in inoculated seedlings on sandy loam soil (89%) when compared to gypseous one (52%). N, P and K concentrations in mycorrhizal seedlings were significantly improved by fungal inoculation. It can be concluded that inoculation of H. sessiliflorum with T. boudieri increased growth attributes and improved plant nutritional status.     

Evidence for mutualist limitation: the impacts of conspecific density on the mycorrhizal inoculum potential of woodland soils

The ability of seedlings to establish can depend on the availability of appropriate mycorrhizal fungal inoculum. The possibility that mycorrhizal mutualists limit the distribution of seedlings may depend on the prevalence of the plant hosts that form the same type of mycorrhizal association as the target seedling species and thus provide inoculum. We tested this hypothesis by measuring ectomycorrhizal (EM) fine root distribution and conducting an EM inoculum potential bioassay along a gradient of EM host density in a pinyon–juniper woodland where pinyon is the only EM fungal host while juniper and other plant species are hosts for arbuscular mycorrhizal (AM) fungi. We found that pinyon fine roots were significantly less abundant than juniper roots both in areas dominated aboveground by juniper and in areas where pinyon and juniper were co-dominant. Pinyon seedlings establishing in pinyon–juniper zones are thus more likely to encounter AM than EM fungi. Our bioassay confirmed this result. Pinyon seedlings were six times less likely to be colonized by EM fungi when grown in soil from juniper-dominated zones than in soil from either pinyon–juniper or pinyon zones. Levels of EM colonization were also reduced in seedlings grown in juniper-zone soil. Preliminary analyses indicate that EM community composition varied among sites. These results are important because recent droughts have caused massive mortality of mature pinyons resulting in a shift towards juniper-dominated stands. Lack of EM inoculum in these stands could reduce the ability of pinyon seedlings to re-colonize sites of high pinyon mortality, leading to long-term vegetation shifts.     

连续三年夜间增温和施氮对云杉外生菌根及菌根真菌多样性的影响

以西南亚高山针叶林建群种粗枝云杉(Picea asperata)为研究对象,采用红外加热模拟增温结合外施氮肥(NH₄NO₃ 25 g N m^-2 a^-1)的方法,研究连续3a夜间增温和施肥对云杉幼苗外生菌根侵染率、土壤外生菌根真菌生物量及其群落多样性的影响。结果表明:夜间增温对云杉外生菌根侵染率的影响具有季节性及根级差异。夜间增温对春季(2011年5月)云杉1级根,夏季(2011年7月)和秋季(2010年10月)云杉2级根侵染率影响显著。除2011年7月1级根外,施氮对云杉1、2级根侵染率无显著影响。夜间增温对土壤中外生菌根真菌的生物量和群落多样性无显著影响,施氮及增温与施氮联合处理使土壤中外生菌根真菌生物量显著降低,但却提高了外生菌根真菌群落的多样性。这说明云杉幼苗外生菌根侵染率对温度较敏感,土壤外生菌根真菌生物量及其群落多样性对施氮较敏感。这为进一步研究该区域亚高山针叶林地下过程对全球气候变化的响应机制提供了科学依据。     

Mycorrhiza formation and growth of Eucalyptus globulus seedlings inoculated with spores of various ectomycorrhizal fungi

 As many eucalypts in commercial plantations are poorly ectomycorrhizal there is a need to develop inoculation programs for forest nurseries. The use of fungal spores as inoculum is a viable proposition for low technology nurseries currently producing eucalypts for outplanting in developing countries. Forty-three collections of ectomycorrhizal fungi from southwestern Australia and two from China, representing 18 genera, were tested for their effectiveness as spore inoculum on Eucalyptus globulus Labill. seedlings. Seven-day-old seedlings were inoculated with 25 mg air-dry spores in a water suspension. Ectomycorrhizal development was assessed in soil cores 65 and 110 days after inoculation. By day 65, about 50% of the treatments had formed ectomycorrhizas. By day 110, inoculated seedlings were generally ectomycorrhizal, but in many cases the percentage of roots colonized was low (<10%). Species of Laccaria, Hydnangium, Descolea, Descomyces, Scleroderma and Pisolithus formed more ectomycorrhizas than the other fungi. Species of Russula, Boletus, Lactarius and Hysterangium did not form ectomycorrhizas. The dry weights of inoculated seedlings ranged from 90% to 225% of the uninoculated seedlings by day 110. Although plants with extensively colonized roots generally had increased seedling growth, the overall mycorrhizal colonization levels were poorly correlated to seedling growth. Species of Laccaria, Descolea, Scleroderma and Pisolithus are proposed as potential candidate fungi for nursery inoculation programs for eucalypts. Accepted: 7 May 1998     

Afforestation of abandoned farmland with conifer seedlings inoculated with three ectomycorrhizal fungi—impact on plant performance and ectomycorrhizal community

The aim of a 3-year study was to investigate whether inoculation of Pinus sylvestris L. and Picea abies (L.) Karst. seedlings with mycorrhizas of Cenococcum geophilum Fr., Piceirhiza bicolorata, and Hebeloma crustuliniforme (Bull.) Quel. has any impact on: 1) survival and growth of outplanted seedlings on abandoned agricultural land, and 2) subsequent mycorrhizal community development. For inoculation, the root system of each plant was wrapped in a filter paper containing mycelium, overlaid with damp peat–sand mixture and wrapped in a paper towel. In total, 8,000 pine and 8,000 spruce seedlings were planted on 4-ha of poor sandy soil in randomized blocks. Already after the first year natural mycorrhizal infections prevailed in the inoculated root systems, and introduced mycorrhizas were seldom found. Yet, the seedlings that had been pre-inoculated with C. geophilum and the P. bicolorata during the whole 3-year period showed significantly higher survival and growth as compared to controls. Moreover, the independent colonization of roots by C. geophilum and the P. bicolorata from natural sources was also observed. A diverse mycorrhizal community was detected over two growing seasons in all treatments, showing low impact of inoculation on subsequent fungal community development. A total of 19 additional ectomycorrhizal morphotypes was observed, which clustered into two well-separated groups, according to host tree species (pine and spruce). In conclusion, the results showed limited ability to increase tree survival and growth, and to manipulate the mycorrhizal community even by extensive pre-inoculations, indicating that fungal community formation in root systems is governed mainly by environmental factors.     

The mycorrhizal fungus Paxillus involutus transports magnesium to Norway spruce seedlings. Evidence from stable isotope labeling

Although it is well established that ectomycorrhizas improve the mineral nutrition of forest trees, there has been little evidence that they mediate uptake of divalent cations such as Mg. We grew nonmycorrhizal seedlings and seedlings mycorrhizal with Paxillus involutus Batsch in a sand culture system with two compartments separated by a 45-μm Nylon mesh. Hyphae, but not roots, can penetrate this net. Labeling the compartment only accessible to hyphae with ²⁵Mg showed that hyphae of the ectomycorrhizal fungus Paxillus involutus transported Mg to their host plant. No label was found in nonmycorrhizal control plants. Our data support the idea that ectomycorrhizas are important for the Mg nutrition of forest trees. This revised version was published online in June 2006 with corrections to the Cover Date.     

Drought effects on fine-root and ectomycorrhizal-root biomass in managed Pinus oaxacana Mirov stands in Oaxaca, Mexico

The effects of a severe drought on fine-root and ectomycorrhizal biomass were investigated in a forest ecosystem dominated by Pinus oaxacana located in Oaxaca, Mexico. Root cores were collected during both the wet and dry seasons of 1998 and 1999 from three sites subjected to different forest management treatments in 1990 and assessed for total fine-root biomass and ectomycorrhizal-root biomass. Additionally, a bioassay experiment with P. oaxacana seedlings was conducted to assess the ectomycorrhizal inoculum potential of the soil for each of the three stands. Results indicated that biomasses of both fine roots and ectomycorrhizal roots were reduced by almost 60% in the drought year compared to the nondrought year. There were no significant differences in ectomycorrhizal and fine-root biomass between the wet and dry seasons. Further, the proportion of total root biomass consisting of ectomycorrhizal roots did not vary between years or seasons. These results suggest that both total fine-root biomass and ectomycorrhizal-root biomass are strongly affected by severe drought in these high-elevation tropical pine forests, and that these responses outweigh seasonal effects. Forest management practices in these tropical pine forests should consider the effects of drought on the capacity of P. oaxacana to maintain sufficient levels of ectomycorrhizae especially when there is a potential for synergistic interactions between multiple disturbances that may lead to more severe stress in the host plant and subsequent reductions in ectomycorrhizal colonization.     

Arbuscular and ectomycorrhizal colonization of two <Emphasis Type="Italic">Eucalyptus</Emphasis> species in semiarid Brazil

Our goal was to evaluate the mycorrhizal colonization, as well as the density of arbuscular mycorrhizal (AM) fungal spores, in Eucalyptus camaldulensis and E. grandis monocultures at 2 years in a semiarid part of Brazil. Soil and root samples were collected in 2 consecutive years. Eucalyptus camaldulensis showed varied AM colonization level according to season of sampling, and Glomus was dominant in spore numbers. Eucalyptus grandis showed dominant ectomycorrhizal (ECM) colonization and lower AM fungal spore density. Overall results suggest that E. camaldulensis has both AM and ECM dependencies, whereas E. grandis is solely ECM dependent in the monocultures.     

Soil fumigation and phosphorus supply affect the formation of Pisolithus-Eucalyptus urophylla ectomycorrhizas in two acid Philippine soils

To examine the effects of microbial populations and external phosphorus supply of two Philippine soils on mycorrhizal formation, Eucalyptus urophylla seedlings were inoculated with two Pisolithus isolates and grown in fumigated, reinfested and unfumigated soil fertilized with four rates of phosphorus. The Pisolithus isolates used were collected from under eucalypts in Australia and in the Philippines. Soils were infertile acid silty loams collected from field sites in Pangasinan, Luzon and Surigao, Mindanao.Significant interaction was observed between inoculation, soil fumigation and phosphorus supply on mycorrhizal formation by the Australian isolate in Surigao soil but not in Pangasinan soil. Soil fumigation enhanced mycorrhizal formation by the Australian isolate but did not affect root colonization by the Philippine isolate. Root colonization by the Australian isolate was highest in the reinfested soil while for the Philippine isolate it was highest in the unfumigated soil. The Australian isolate was more effective than the Philippine isolate in promoting growth and P uptake of E. urophylla seedlings in both soils. Total dry weight and P uptake of E. urophylla seedlings inoculated with the Australian isolate were maximum in fumigated and in the reinfested Pangasinan and Surigao soils supplied with 8 mg P kg^-1 soil. In the unfumigated soil, growth of seedlings inoculated with the Australian isolate was significantly reduced. Seedlings inoculated with the Philippine isolate had the largest dry weights and P contents in unfumigated Pangasinan and Surigao soils supplied with 8 mg P kg^-1 soil.These results indicate that the performance of the Australian Pisolithus isolate was markedly affected by biological factors in unfumigated soil. Thus, its potential use in the Philippines needs to be thoroughly tested in a variety of unfumigated soils before its widespread use in any inoculation programme.     

Effects of isolates of ectomycorrhizal fungi and endophytic Mycelium radicis atrovirens that were dominant in soil from disturbed sites on growth of Betula platyphylla var. japonica seedlings

Effects of ectomycorrhizal fungi and endophytic Mycelium radicis atrovirens Melin (MRA) on growth of Betula platyphylla var. japonica seedlings were investigated under aseptic culture conditions. Three isolates of ectomycorrhizal fungi and two isolates of MRA were used. One MRA isolate was Phialocephala fortinii. Previous field work revealed that these isolates were dominant on the roots of B. platyphylla var. japonica seedlings grown in a mineral subsoil that had been exposed by the removal of surface soil. After a 100-day incubation, the growth of the seedlings was significantly enhanced by the colonization of these ectomycorrhizal fungal isolates as compared with uninoculated seedlings. In contrast, the growth of seedlings was retarded by the colonization of the MRA isolates. The growth of seedlings that were co-inoculated with ectomycorrhizal fungi and MRA was similar to that of uninoculated seedlings in most cases. These results suggest that ectomycorrhizal fungi have a beneficial effect on the growth of B. platyphylla var. japonica seedlings and that they suppress the deleterious effect of MRA. Thus, these ectomycorrhizal fungi probably have an important role in establishing B. platyphylla var. japonica seedlings during the initial stage of re-vegetation following site disturbance by the removal of surface soil.     

Recovery of mycorrhizas of a fungus, <Emphasis Type="Italic">Cenococcum geophilum</Emphasis>, after urea treatment in warm temperate forests in Japan

We studied recovery of the ectomycorrhizal species Cenococcum geophilum (Cg) after urea treatment in two types of vegetation. The recovery was as quick as 6 months after the treatment and overlapped the fruiting period of ectomycorrhizal ammonia fungi. Ectomycorrhizas investigated as Cg belonged to a single species irrespective of treatment and vegetation type. Cg ectomycorrhizas were significantly more abundant in density in nontreated soil than in treated soil. Between vegetation types, Cg ectomycorrhizas were significantly more in density in broad-leaved deciduous forest than in broad-leaved evergreen forest. Moreover, Cg was dominant in the nontreated soils of the former type of forest.     

Ectomycorrhizal types and endobacteria associated with ectomycorrhizas of Morchella elata (Fr.) Boudier with Picea abies (L.) Karst

Subterranean morel sclerotia connected with ascomata of Morchella elata (Fr.) Boudier were found to surround 155 ectomycorrhizal root tips of Picea abies (L.) Karst, belonging to seven different types. Based upon anatomical and cytological studies, three ectomycorrhizal types could be attributed to types already described, whereas four types appeared to be undescribed. The nature of the association between the morel and the mycorrhizal types was dependent on the type and was not related to their vitality. In particular, morel ectomycorrhizas formed secondarily and exclusively by succeeding to primary mycorrhizas of a heterobasidiomycete. In addition to this triple association, an endobacterium was observed growing within the Hartig net of this heterobasidiomycete mycorrhiza. The significance of this complex of associations for the formation of ectomycorrhizas by the morel is discussed.     

Use of soil transfer for reforestation on abandoned mined lands in Alaska

Soil transfers from an intermediate successional site and a mature forest site were applied to Populus balsamifera L. cuttings and Alnus crispa (Ait.) Pursh seedlings placed on an abandoned mined site in south central Alaska to improve plant establishment. Mycorrhizal fungi in the soil transfers from the two successional stages were hypothesized to have different effects on plant species that colonize disturbed sites at different times or on different substrates. The site consisted of coarse, dry, low-nutrient spoils and was naturally colonized by scattered P. balsamifera but not A. crispa, although seed sources for both were adjacent to the site. Physical dimensions of the transplanted seedlings and cuttings were measured at the beginning and end of each growing season. Selected plants were harvested at the end of the 2-year study and examined for mycorrhizal formation, current growth, and leaf tissue nutrient concentrations. Both plant species were taller when treated with the soil transfers from the mature forest than with soils from the intermediate site although the increase for A. crispa was greater. Physical dimensions, current growth, and nutrient concentrations were greater when A. crispa was treated with the mature soil transfer compared with the intermediate soil transfer. Mycorrhizae which infected Alnus were predominantly a brown woody type, while other types accounted for greater relative mycorrhizal infection percentage on Populus. Insufficient quantities of mycorrhizal inoculum of suitable species, as well as low moisture and low nutrient conditions, may be factors limiting A. crispa colonization on primary disturbed sites in south central Alaska.     

Quantities and types of ectomycorrhizal and endophytic fungi associated with Betula platyphylla var. japonica seedlings during the initial stage of establishment of vegetation after disturbance

Ectomycorrhizal and endophytic fungi of Betula platyphylla Sukatchev var. japonica Hara seedlings were investigated by bioassay using soils from sites where the surface layer had been removed by destructive disturbances. Soil samples were taken from sites A, B, C and D, where 1, 2–3, 4–5, and 7–8 years, respectively had passed since disturbance. Naturally regenerated B. platyphylla var. japonica seedlings grew at sites C and D, but not at sites A or B. The percentages of ectomycorrhizal formation in seedlings were significantly lower in the soils from site A (4%) and site B (13%), compared to those in the soils from site C (53%) and site D (37%). The numbers of ectomycorrhizal morphologic types in sites A, B, C, and D were eight, five, one, and seven, respectively. The same dominant type of ectomycorrhiza was found in sites C and D, and this type was different from those in sites A and B. The frequencies of colonization of seedling roots by endophytic fungi, especially Mycelium radicis atrovirens Melin (MRA) in soils from sites A and B were 31 and 33%, respectively; these frequencies were significantly higher than those for site C (0%) and site D (2%). During the initial stage of establishment of vegetation following disturbance, the quantities and types of ectomycorrhizal fungi in the field that have the potential to associate with B. platyphylla var. japonica might rapidly change after invasion of the host plant. Ectomycorrhizal fungi seemed to compete with endophytic MRA fungi for colonization of the roots of B. platyphylla var. japonica seedlings.     

Morphological classification of ectomycorrhizas ofPinus densiflora

Morphological classification of ectomycorrhizas ofPinus densiflora was conducted. Fifty soil samples containing pine ectomycorrhizas, and 40 pine seedlings were collected randomly in two separate reforested stands ofP. densiflora (45 yr old) from May 1992 to October 1994. Fifty-six types of ectomycorrhizas could be classified based upon microscopically observable morphological characteristics. Fifty percent of the types showed cystidia or other specific characteristics such as laticiferous hyphae in the fungal sheaths, verrucose emanating hyphae and a positive hyphal reaction to UV irradiation. Four mycorrhizal types were confirmed to be formed by the fungiRussula delica, R. mariae, R. nigricans, andCenococcum geophilum, respectively. Although the other 52 types were unidentified mycobionts at species level, it was inferred that they were formed by the fungiHebeloma, Lactarius, Russula andTuber. There was a slight difference in the observed mycorrhizal types between the tree ages. Contribution No. 127, Laboratories of Plant Pathology and Mycology, Institute of Agriculture and Forestry, University of Tsukuba.     

Respiration activity of ectomycorrhizas from Cenococcum geophilum and Lactarius sp. in relation to soil water potential in five beech forests

Forest trees are involved in root symbioses with hundreds of species of ectomycorrhizal fungi which constitute functional guilds able to improve the water and mineral nutrition of host trees. In temperate ecosystems, water shortage is a main factor limiting tree vitality. To assess how soil water conditions affected the physiological state of beech (Fagus silvatica L.) ectomycorrhizal roots, we monitored glucose respiration of two ectomycorrhizal types (Lactarius sp. and Cenococcum geophilum) during two complete growing seasons. Five stands of contrasting soil conditions were chosen in north-eastern France. The top soil horizons were equipped with micropsychrometers for measuring water potential and temperature. Glucose respiration on individual ectomycorrhizas was measured in vitro by trapping [¹⁴C]-CO₂ from radiolabelled glucose. For soil water potential <-0.2 MPa, the potential respiration activity of C. geophilumectomycorrhizas was significantly less altered than that of Lactariussp. ectomycorrhizas, indicating that C. geophilumis more likely than Lactariussp. to maintain the physiological integrity of beech roots facing drought stress.     

Laboratory experiments imply the conditionality of mycorrhizal benefits for Salix repens: role of pH and nitrogen to phosphorus ratios

Responses of one arbuscular mycorrhizal fungus (Glomus mosseae) and two ectomycorrhizal fungi (Hebeloma leucosarx, Paxillus involutus) to a range of substrate conditions were investigated in the laboratory. Non-mycorrhizal controls were also included. Substrate conditions included three levels of nitrogen – phosphorus ratios, ranging from N limitation to P limitation (N/P ratio 5.4, 16.2, 48.6), and three pH's, ranging from acidic to alkaline (pH 4, 5.5, 7), in a full factorial experiment. Plant parameters (carbon gain, N and P-content, root length) were significantly affected by fungus, soil pH and soil N/P, and their interactions. Mycorrhizal benefits by ectomycorrhizal fungi (EcMF) were generally larger than by the arbuscular mycorrhizal fungi (AMF), when assessed by above-ground parameters. Glomus mosseae, despite low colonization, had a much larger positive effect on root length than those EcMF. Hebeloma leucosarx and P. involutus were equally effective, despite differences in proportional colonization. Hebeloma leucosarx was able to expand niche width of S. repens towards alkaline conditions. Results are discussed in the framework of a dune successional gradient from young, calcareous, humus-poor towards old, acidic, humus-rich soils.