Ectomycorrhizal Root Colonization Research Articles

Facilitation of American Chestnut (Castanea dentata) Seedling Establishment byPinus virginianain Mine Restoration

This study evaluated the influence of planting sites on the establishment and ectomycorrhizal (ECM) colonization of American chestnut (Castanea denetata(Marsh.) Borkh.) on an abandoned coal mine in an Appalachian region of the United States. Root morphotyping and sequencing of the fungal internal transcribed spacer (ITS) region were used to identify the ECM species associated with the chestnut seedlings. Germination, survival, ECM root colonization, and growth were assessed in three habitats: forest edge, center (plots without vegetation), and pine plots (a 10-year-old planting ofPinus virginiana). Seedlings in pine plots had higher survival (38%) than the other plot types (center 9% and forest edge 5%;P=0.007). Chestnuts found colonized by ECM within the pine plots were larger (P=0.02), contributed by a larger root system (P=0.03). Forest edge and pine plots had more ECM roots than seedlings in center plots (P=0.04). ITS fungal sequences and morphotypes found among chestnut and pine matchedScleroderma, Thelephora,andPisolithussuggesting these two plant species shared ECM symbionts. Results indicated that the presence ofP. virginianahad a greater facilitative effect on growth and survival of chestnut seedlings.

Assessment of mycorrhizal colonisation and soil nutrients in unmanaged fire-impacted soils from two target restoration sites

The mycorrhizal colonisation of plants grown in unmanaged soils from two restoration sites with a fire history in Northern Portugal was evaluated from the perspective of supporting restoration programmes. To promote restoration of original tree stands, Quercus ilex L. and Pinus pinaster Ait. were used as target species on two sites, denoted Site 1 and 2 respectively. The aim of the study was to assess whether mycorrhizal propagules that survived fire episodes could serve as in situ inoculum sources, and to analyse the spatial distribution of soil nutrients and mycorrhizal parameters. In a laboratory bioassay, P. pinaster and Q. ilex seedlings were grown on soils from the target sites and root colonisation by ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) fungi was determined. The ECM root colonisation levels found indicated that soil from Site 2 contained sufficient ECM propagules to serve as a primary source of inoculum for P. pinaster. The low levels of ECM and AM colonisation obtained on the roots of plants grown in soil from Site 1 indicated that the existing mycorrhizal propagules might be insufficient for effective root colonisation of Q. ilex. Different ECM morphotypes were found in plants grown in soil from the two sites. At Site 2 mycorrhizal parameters were found to be spatially structured, with signif icant differences in ECM colonisation and soil P concentrations between regions of either side of an existing watercourse. The spatial distribution of mycorrhizal propagules was related to edaphic parameters (total C and extractable P), and correlations between soil nutrients and mycorrhizal parameters were found.

Does herbivory really suppress mycorrhiza? A meta‐analysis

Summary 1. aged and natural ecosystems, herbivory can have a major impact on plant growth. Defoliation and shoot removal reduce the photosynthetic capacity of plants and are also thought to reduce allocation of carbon to roots and mycorrhizal fungi. However, evidence supporting this assumption remains equivocal. 2. ducted a meta‐analysis of 99 experiments, from 33 publications, measuring arbuscular and ectomycorrhizal colonization of roots after real or simulated herbivory removed leaves or shoots. We also explored how effects were moderated by the type of mycorrhiza, fertilization, experimental setting (laboratory or field), treatment (real herbivory of shoots, real herbivory of leaves, simulated herbivory of shoots, simulated herbivory of leaves), type of host plant, duration of the experiment and year of publication. 3. Overall, herbivory reduced mycorrhizal colonization by about 3 percentage points. Treatment, host plant type and year of publication were the only significant moderators, with real or simulated herbivory of leaves and real herbivory of shoots suppressing colonization, while simulated removal of shoots tended to increase colonization. Herbivory reduced colonization of perennial grasses and deciduous trees by about 4 and 8 percentage points, respectively. Mycorrhizal colonization of annual crops was reduced by about 12 percentage points, although this was not significantly different from zero. Mycorrhizal colonization of perennial forbs and evergreen trees was also unaffected by herbivory, and colonization of mixtures of perennial grasses and forbs increased by about 15 percentage points following herbivory. Effect size increased with year of publication, likely due to shifts in experimental designs towards systems more likely to show positive effects of herbivory on mycorrhiza. 4. Synthesis. Our results challenge the carbon‐limitation hypothesis and suggest that herbivory, real or simulated, reduces mycorrhizal colonization by biologically meaningful amounts only in a limited subset of systems.

Negligible contribution from roots to soil-borne phospholipid fatty acid fungal biomarkers 18:2ω6,9 and 18:1ω9

The phospholipid fatty acid biomarkers 18:1ω9, 18:2ω6,9 and 18:3ω3,6,9 are commonly used as fungal biomarkers in soils. They have, however, also been found to occur in plant tissues, such as roots. Thus, the use of these PLFAs as fungal biomarkers in sieved soil, which may still contain small remains of roots, has been questioned. We used data from a recent beech tree girdling experiment to calculate the contribution of roots to these biomarkers and were able to demonstrate that not more than 0.61% of 18:1ω9 and 18:2ω6,9 in sieved soil samples originated from roots (but 4% of 18:3ω3,6,9). Additionally, the abundance of the biomarker 18:2ω6,9 in the soil was found to be highly correlated to ectomycorrhizal root colonization, which further corroborates its fungal origin. PLFA biomarkers were substantially reduced in vital roots from girdled trees compared to roots of control trees (by up to 76%), indicating that the major part of PLFAs measured in roots may actually originate from ectomycorrhizal fungi growing inside the roots. We calculated, that even a near to 50% reduction in fine root biomass – as observed in the girdling treatment – accounted for only 0.8% of the measured decrease of 18:2ω6,9. Our results demonstrate that both 18:1ω9 and 18:2ω6,9 are suitable biomarkers for detecting fungal dynamics in soils and that especially 18:2ω6,9 is a reliable biomarker to study mycorrhizal dynamics in beech forests.

Effect of Ectomycorrhizae and various levels of phosphorus on growth and biomass of Cedrus deodara (Roxb. Ex Lamb.) under nursery conditions

Pot experiments were carried out under nursery conditions during 2005-2006 to study the response of Deodar seedlings to inoculations with ectomycorrhizae (Pisolithus tinctorius, Laccaria laccata and Suillus granulatus), forest litter and different levels of phosphorus. Various plant growth characteristics (plant height, root length, collar diameter and plant biomass) and ectomycorrhizal root colonization responded significantly to ectomycorrhizal inoculation, forest litter and phosphorus. Among the ectomycorrhiae, inoculation of Pisolithus tinctorius proved most beneficial for all plant growth parameters and ectomycorrhizal root colonization followed by Laccaria laccata and Suillus granulatus. The treatment combination of Pisolithus tinctorius along with phosphorus dose of 75 mg plant-1 proved to be the best treatment for all the studied characteristics.

Field persistence of the edible ectomycorrhizal fungus Lactarius deliciosus: effects of inoculation strain, initial colonization level, and site characteristics

Pinus pinea plants were inoculated with different strains of the edible ectomycorrhizal fungus Lactarius deliciosus. The inoculated plants were established in six experimental plantations in two sites located in the Mediterranean area to determine the effect of the initial colonization level and the inoculated strain on fungal persistence in the field. Ectomycorrhizal root colonization was determined at transplantation time and monitored at different times from uprooted plants. Extraradical soil mycelium biomass was determined from soil samples by TaqMan(R) real-time polymerase chain reaction (PCR). The results obtained indicate that the field site played a decisive role in the persistence of L. deliciosus after outplanting. The initial colonization level and the selection of the suitable strain were also significant factors but their effect on the persistence and spread of L. deliciosus was conditioned by the physical-chemical and biotic characteristics of the plantation soil and, possibly, by their influence in root growth. Molecular techniques based on real-time PCR allowed a precise quantification of extraradical mycelium of L. deliciosus in the field. The technique is promising for non-destructive assessment of fungal persistence since soil mycelium may be a good indicator of root colonization. However, the accuracy of the technique will ultimately depend on the development of appropriate soil sampling methods because of the high variability observed.

Influence of water-stress acclimation and Tuber melanosporum mycorrhization on Quercus ilex seedlings

Mycorrhizal and non-mycorrhizal holm oak (Quercus ilex L.) seedlings inoculated with black truffle (Tuber melanosporum) were grown under nursery conditions and subjected to drought hardening for 4 months in autumn and winter followed by irrigation for 10 days. Leaf water potential and stomatal conductance were monitored during the 4 months of drought. When the test was completed (March), measurements were made for each treatment (inoculated or non-inoculated), and watering regime (watered and water-stressed). Pressure–volume curves, osmotic potential at full turgor, osmotic potential at zero turgor and the tissue modulus of elasticity near full turgor were calculated. Mycorrhizal colonization and growth, and the content of the main mineral nutrients N, P, K, Ca and Mg were measured. Water stress affected plant growth, caused an elastic adjustment of the plant tissues, and decreased the P and K content, and inoculation improved the nitrogen content. Drought acclimation apparently achieved the goal of improving the drought tolerance of holm oak seedlings, without depressing ectomycorrhizal root colonization by T. melanosporum.

Soil factors influencing the growth response of Acacia holosericea A. Cunn. ex G. Don to ectomycorrhizal inoculation

Australian acacias like Acacia holosericea are excellent candidates for the revegetation of arid zones in Africa. Their high ability to develop multiple symbioses with soil microorganisms is crucial to their rapid development in adverse climatic and edaphic conditions. These symbioses include nitrogen fixation with rhizobia, vesicular arbuscular mycorrhization and ectomycorrhization. We set up an experiment to test the growth response of A. holosericea to ectomycorrhizal inoculation in 13 different soils from Senegal. After autoclaving the soil, the experiment was conducted in a greenhouse for four weeks. Plants were inoculated with Pisolithus albus strain IR100. The following parameters were measured: plant biomass, N, P, K and Ca foliar composition, spontaneous nodulation rate, and ectomycorrhizal colonization. Data were analyzed in light of the physical, chemical and total microbial characteristics of the soil. The results demonstrated a global promoting effect of P. albus inoculation on plant (shoot and root) growth and on foliar P and K, together with a depressive effect on N, while Ca rates were barely affected. Interestingly, spontaneous nodulation with putative water- or airborne rhizobia was stimulated after P. albus inoculation. However, these nodules seemed poorly effective, as they failed to cause any change in plant growth or in foliar N composition within the nodulated and nonnodulated control plants. These results show that plant growth response to ectomycorrhizal inoculation is greatly dependent on soil characteristics, and that root ectomycorrhizal colonization is influenced by biotic factors such as soil microbiota. From a practical point of view, data from the present study demonstrate that it is possible to optimize the effect of fungi on plant growth by screening soils under nursery conditions.

Effects of nitrogen with and without acidified sulphur on an ectomycorrhizal community in a Sitka spruce ( Picea sitchensis Bong. Carr) forest

This preliminary study investigated the effects of enhanced nitrogen (NH 4NO 3 at 48 kg ha −1 y −1), sulphur (Na 2SO 4 at 50 kg ha −1y −1), acidified nitrogen and sulphur (H 2SO 4 + NH 4NO 3) at pre-stated doses (pH 2.5), and acidified nitrogen and sulphur deposition at double these doses on the ectomycorrhizal community associated with a 13-year-old Sitka spruce ( Picea sitchensis) forest. Sulphur deposition had little impact on below ground ectomycorrhizal diversity, but stimulated sporocarp production. Nitrogen inputs increased below ground colonisation compared to acidified nitrogen and sulphur, largely due to an increase in Tylospora fibrillosa colonisation. Sporocarp production and ectomycorrhizal root colonisation by Lactarius rufus were reduced in the nitrogen treated plots. These observations suggest that nitrogen deposition to a young plantation may suppress ectomycorrhizal fungi producing large sporocarps. It is proposed that enhanced nitrogen deposition increases ectomycorrhizal nitrogen assimilation, consuming more carbon and leaving less for extrametrical mycelium and sporocarp development.

Ectomycorrhizal colonization and seedling growth of Shorea (Dipterocarpaceae) species in simulated shade environments of a Sri Lankan rain forest

The purpose of our study was to examine whether the degree of ectomycorrhizal (EM) colonization was associated with amount of shade for potted seedlings of five rain forest tree species. Seedlings were exposed to a range of shade treatments—from the open to that emulating the degree of shade beneath a deep-canopied forest. The experiment was carried out at the field station (580 m.a.s.l) of the Sinharaja World Heritage Site in southwestern Sri Lanka. We selected five species for the study: Shorea affinis (Thw.) Ashton, S. congestiflora (Thw.) Ashton, S. cordifolia (Thw.) Ashton, S. gardneri (Thw.) Ashton, and S. zeylanica (Thw.) Ashton, all members of a sympatric clade of endemic canopy trees in the family dipterocarpaceae. Results show that the percentage EM colonization was significantly different among shade treatments, for all five species ( p < 0.05). However, EM root colonization was not significantly different among species. Highest percentages of EM colonization for all species, except for S. congestiflora, were in treatments providing full open conditions. However, seedling growth of all species were best under partial shade conditions ( p < 0.05), intermediate between the deep shade of a forest understory and no shade of open environments. The non-linear relationship between seedling growth performance and EM colonization is discussed.

The effect of soil pH on the ability of ectomycorrhizal fungi to increase the growth of Eucalyptus globulus Labill.

We examined the effect of two levels of soil pH (5 and 6) on the ability (effectiveness) of ectomycorrhizal fungi to increase the growth of Eucalyptus globulus Labill. at a deficient supply of P. Plants were inoculated with one of six fungal isolates [Laccaria laccata (Scop. ex Fr.) Berk. and Br. (isolates A and B), Pisolithus tinctorius (Pers.) Coker and Couch (isolates A and B), Descolea maculata Bough. and Mal. and Setchelliogaster sp. nov.] and were grown in a P-deficient sand, in pots, in a temperature-controlled glasshouse. Seedlings were harvested 89 days after planting and were assessed for dry matter production, tissue P concentrations, ectomycorrhizal colonization of roots and hyphal development in soil.

The survival and development of inoculant ectomycorrhizal fungi on roots of outplanted Eucalyptus globulus Labill

The survival and development of two inoculant ectomycorrhizal fungi (Hebeloma westraliense Bough. Tom. and Mal. and Setchelliogaster sp. nov.) on roots of outplanted Eucalyptus globulus Labill. was examined at two expasture field sites in the south-west of Western Australia. Site 1 was a gravelly yellow duplex soil, and Site 2 was a yellow sandy earth. Plants were grown in steamed or unsteamed soil, in root bags designed as field containers for young growing trees. Three, 6 and 12 months after outplanting, plants were removed from these bags and assessed for dry weights of shoots and ectomycorrhizal colonization of roots. The inoculant ectomycorrhizal fungi (identified on the basis of the colour and morphology of their mycorrhizas) survived on roots of E. globulus for at least 12 months after outplanting at both field sites. At Site 1, however, colonization of new fine roots by the inoculant fungi was low (less than 20% of fine root length). Inoculation had no effect on the growth of E. globulus at this site. In contrast, at Site 2 the inoculant ectomycorrhizal fungi colonized up to 30–50% of new fine root length during the first 6 months after outplanting. There was a corresponding growth response to ectomycorrhizal inoculation at this site, with a close relationship (r2=0.82**) between plant growth at 12 months and root colonization at 3 months. Plant growth at 12 months was related less closely with root colonization at 6 or 12 months. Root colonization by ‘resident’ ectomycorrhizal fungi increased with time at both field sites. At Site 2, this increase appeared to be at the expense of colonization by the inoculant fungi, which was reduced to less than 10% of fine root length at 12 months. Steaming the soil had little effect on colonization by the inoculant ectomycorrhizal fungi at either field site, but decreased colonization by the resident ectomycorrhizal fungi.

Ectomycorrhizal fungal succession in jack pine stands following wildfire

SUMMARYA study was conducted to determine if ectomycorrhizal fungi in an age sequence of jack pine (Pinus banksiana Lamb.) stands which had regenerated following wildfire disturbance followed a successional pattern. Ectomycorrhizal development and number of symbionts were assessed in the forest floor and 0‐20 cm deep mineral soil in 6, 41, 65 and 122‐yr‐old stands by conducting a macrofungal fruit body survey and examining pine root tips microscopically for mycorrhizal status and types of fungi forming the symbiosis. The majority of roots were located in the mineral soil with no substantial invasion of the forest floor except in the 122‐yr‐old stand. Over 90 % of the jack pine root tips were mycorrhizal and the majority of fruit bodies were produced by ectomycorrhizal species, regardless of stand age. There was no decrease in ectomycorrhizal colonization of roots with stand age. Both fruit body and root assessments revealed a distinct sequence of mycorrhizal fungi with stand age consisting of early‐stage fungi [Coltricia perennis (L:Fr.) Murr., Thelephora spp., E‐strain]; multi‐stage fungi [Suillus brevipes (Pk.) Kuntze, Inocybe spp., Cenococcum geophilum Fr., Mycelium radicis atrovirens Melin] and late‐stage fungi [Cortinarius spp., Lactarius spp., Russula spp., Tricholoma spp., Hygrophorus spp., Hydnellum peckii Banker, Suillus tomentosus (Kauff.) Sing., Snell &amp; Dick, Piloderma byssinum (Karst.) Jül. and Sarcodon scabrosus (Fr.) Karst.]. Many of the basidiomycete species fruiting above ground were detected also on the roots below ground. Fruit bodies of SO species of ectomycorrhizal fungi were recorded while 39 distinct mycorrhizal types were identified on the roots. There was a significant increase in mycorrhizal species richness between the 6 and 41‐yr‐old stands and this was primarily the result of partial replacement of Suillus brevipes on the 6‐yr‐old trees by late‐stage fungi in the older stands. Very few species present in the 6‐yr‐old stand were completely replaced in the older stands; rather, the multi‐stage species present in the young stand were joined by late‐stage species in the mature stands. The species abundance distribution of fungi on the roots in the 6‐yr‐old stand was best described by a geometric series which is typical of an early successional community while the distributions in the three oldest stands conformed to a lognormal series which is indicative of a stable, species rich community. Both the composition and structure of the ectomycorrhizal community had stabilized 41 yr after wildfire.

Boron fertilization, ectomycorrhizal colonization, and growth of Pinusechinata seedlings

Shortleaf pine (Pinusechinata Mill.) seedlings inoculated with Pisolithustinctorius (Pers.) Coker and Couch or left uninoculated were grown in book planters for 16 weeks. Seedlings were fertilized with 25 μg mL−1 of borate applied to the foliage as a mist, to the soil as a solution, or to both the foliage and the soil. B applied to the foliage or to the soil significantly increased ectomycorrhizal colonization of roots and seedling growth. Growth of uninoculated seedlings was not enhanced by B fertilization. The lack of growth response of uninoculated seedlings as contrasted with increased infection and growth of inoculated seedlings suggests that B affects the fungal symbiont or the plant host–symbiont combination to a greater extent than the plant host alone.