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.     

Ability of ectomycorrhizal fungi to utilize starch and related substrates

Basidiomycetous fungi of 55 strains of 33 species in 15 genera which are thought to be ectomycorrhizal were grown on starch and related substrates as a sole carbon source, and their ability to utilize these substrates was determined. Mycellial weights of the fungi grown on agar media containing starch and amylose varied between the strains from 1.1 to 94.9 mg/flask and from 0.4 to 93.3mg/flask, respectively. Mycelial growth rates ranged from 0 to 1.17 mm/d on barley grain medium and from 0 to 2.03 mm/d on rice grain medium; the highest rate corresponded to about half of the average of reference wood-rotting fungi. Most of the mycorrhizal fungi that grew well on amylose gave higher growth rates on barley. Several strains inLyophyllum, Hebeloma, Sarcodon, andTricholoma grew well on both glucose and starch media.     

The screening and selection of inoculant arbuscular-mycorrhizal and ectomycorrhizal fungi

The initiation of a programme of screening and selection of arbuscular-mycorrhizal fungi (AM fungi) and ectomycorrhizal fungi (ECM fungi) for use as inoculant fungi in agriculture, horticulture of forestry will depend on whether inoculation is more appropriate as a management option than manipulation of the indigenous mycorrhizal populations. The greatest immediate potential for the successful use of mycorrhizal inoculants will be in soils and growth media where phosphorus (P) limits plant growth and where the indigenous mycorrhizal fungi are either ineffective at increasing P uptake by the plant or their numbers have been drastically reduced by human influence or natural disturbance. In recent investigations, however, additional benefits to the plant following colonization of roots by effective AM or ECM fungi have been demonstrated. These additional benefits of an effective mycorrhizal association have necessitated a re-evaluation of the optimum screening procedures for isolates of AM and ECM fungi. Both current methodologies and suggestions for alternative approaches to the screening of AM and ECM fungi are discussed in this paper. The problems inherent in choosing suitable experimental conditions to compare different isolates at the screening stage are also addressed. The review also stresses the importance of continued monitoring of introduced mycorrhizal fungi to learn more about their longer-term ecological role, particularly within reforestation or revegetation studies.     

The effects of cadmium and the cadmium-zinc interaction on the axenic growth of ectomycorrhizal fungi

Eleven strains of ectomycorrhizal fungi belonging to seven species have been cultured on a cadmium-contaminated growth medium in order to determine their in vitro cadmium tolerance. Four strains were collected from a zinc and cadmium-polluted soil. Radial growth rate was a sensitive parameter to detect Cd toxicity. A wide differential response to Cd was obtained between the individual species. A clear relation between Cd tolerance and site origin of the isolates did not exist, although such a relationship was found when strains are compared within one species. Cd-sensitive and Cd-tolerant strains of Suillus bovinus were studied in more detail. Two isolates were grown on media with combinations of two non-toxic zinc concentrations and three cadmium levels. Adding a higher Zn concentration to the medium resulted in a reduction of the toxic effect of Cd. This antagonistic effect also resulted in a lowered Cd concentration in the mycelium.     

Effects of phosphorus supply on growth and nitrogen fractions in xylem sap and foliage of Eucalyptus regnans (F.Muell.), E. nitens (Maiden) and E. globulus (Labill.) seedlings: implications for herbivory

Rates of growth of seedlings of E. globulus, E. regnans and E. nitens were related to phosphorus supply in two soils but concentrations of total nitrogen and total phosphorus in most plant tissues did not vary significantly among soil or phosphorus treatments. Differences in concentrations of nitrogen and phosphorus and in the composition of the pool of free amino-acids among leaves at different stages of development were far greater than differences between treatments. The most significant of these differences were several-fold greater concentrations of arginine in the oldest leaves and these are most likely due to protein degradation and/or in situ synthesis since arginine is not generally phloem mobile. The concentration of reduced nitrogen in xylem sap was inversely related to growth and glutamine was by far the dominant nitrogenous solute. We suggest that specific nitrogenous solutes may be useful indices of the nitrogen status of eucalypt tissues for insect herbivores.     

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     

Effects of bacteria on mycorrhizal development and growth of container grown Eucalyptus diversicolor F. Muell. seedlings

The development of ectomycorrhizas on inoculated eucalypt seedlings in commercial nurseries is often slow so that only a small percentage of roots are mycorrhizal at the time of outplanting. If mycorrhizal formation could be enhanced by co-inoculation with bacteria which promote rapid root colonisation by specific ectomycorrhizal fungi, as demonstrated by certain bacteria in the Douglas fir-Laccaria bicolor association, this would be of advantage to the eucalypt forest industry. Two bacterial isolates with a demonstrated Mycorrhization Helper Bacteria (MHB) effect on ectomycorrhiza formation between Pseudotsuga menziesii and Laccaria bicolor (S238), and seven Western Australian bacterial isolates from Laccaria fraterna sporocarps or ectomycorrhizas were tested in isolation for their effect on ectomycorrhizal development by three Laccaria spp. with Eucalyptus diversicolor seedlings. Mycorrhizal formation by L. fraterna (E710) as measured by percentage infected root tips, increased significantly (p < 0.05) by up to 296% in treatments coinoculated with MHB isolates from France (Pseudomonas fluorescens Bbc6 or Bacillus subtilis MB3), or indigenous isolates (Bacillus sp. Elf28 or a pseudomonad Elf29). In treatments coinoculated with L. laccata (E766) and the MHB isolate P. fluorescens (Bbc6) mycorrhizal development was significantly inhibited (p < 0.05). A significant Plant Growth Promoting Rhizobacteria (PGPR) effect was observed where the mean shoot d.w. of seedlings inoculated only with an unidentified bacterium (Elf21), was 49% greater than the mean of uninoculated controls (-fungus, -bacterium). Mean shoot d.w. of seedlings coinoculated with L. bicolor (S-238), which did not form ectomycorrhizas with E. diversicolor, and an unidentified bacterium (Slf14) or Bacillus sp. (Elf28) were significantly higher than uninoculated seedlings or seedlings inoculated with L. bicolor (S-238) alone. This is the first time that an MHB effect has been demonstrated in a eucalypt-ectomycorrhizal fungus association. These organisms have the potential to improve ectomycorrhizal development on eucalypts under nursery conditions and this is particularly important for fast growing eucalypt species where the retention time of seedlings in the nursery is of short duration (2–3 months).     

A comparison of arbuscular and ectomycorrhizal Eucalyptus coccifera: growth response, phosphorus uptake efficiency and external hyphal production

Eucalyptus coccifera Hook., a plant capable of forming both arbuscular mycorrhizas and ectomycorrhizas, was used to compare the effects of the two mycorrhizal types on phosphorus uptake and C allocation. Seedlings were grown in a P-deficient soil/sand mixture inoculated with peat/vermiculite spawn of Laccaria bicolor (Maire) Orton or Thelephora terrestris (Ehrh.) Fr.; or with 250-μm sievings from leek colonized by Glomus caledonium (Nicol. & Gerd.) Trappe & Gerde., Glomus sp. type E3 or Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe or with autoclaved spawn (non-mycorrhizal control). Before the 89-d harvest, a subset of the harvested plants was labelled with ¹⁴C (45–60-min pulse, 202-h chase). Growth promotion and the increase in seedling P content was largest in the two ectomycorrhizal treatments. Production of fluorescein diacetate-stained external hyphae was three to seven times higher by ectomycorrhizal (ECM) fungi compared with arbuscular mycorrhizal (AM) fungi and was highly correlated with P uptake and shoot weight. Phosphorus inflow rates of ECM and AM seedlings were 3·8 times, and 2·0–2·7 times those of non-mycorrhizal seedlings. Phosphorus acquisition efficiencies were similar (11·2 and 10·0 μmol P mmol⁻¹C for T. terrestris and Glomus E3 plants, respectively) for the two mycorrhizal types, and appeared to be greater than in uninoculated plants (7.2 μmol P mmol⁻¹C) grown at the same P level.     

Response of Eucalyptus camaldulensis Dehnh., E. globulus Labill. ssp. globulus and E. grandis W.Hill to excess boron and sodium chloride

In a sand culture experiment we investigated the effects of boron (0.01, 0.19, 0.46 and 0.93 mol m⁻³ B, as H₃BO₃), sodium chloride (0, 100 and 200 mol m⁻³ NaCl) and combined B and NaCl, over 36 days, on growth, water use and foliar ion concentrations of nine week-old seedlings of three fast-growing, commercial eucalypts ( Eucalyptus camaldulensis Dehnh. , E. globulus Labill. ssp. globulus and E. grandis W.Hill.). Shoot dry weight was significantly reduced by high concentrations of NaCl (p < 0.001) and by B and NaCl in combination (p ≤ 0.05) but not by B alone. Root dry weight was significantly reduced by both NaCl (p < 0.001) and B (p < 0.001), but not by combined B and NaCl. Foliar B concentrations increased with higher concentrations of applied B and decreased with higher NaCl concentrations. Foliar Na concentrations were greater with higher NaCl concentrations, whereas B application had no significant effect on foliar Na concentrations. All three species accumulated relatively high B concentrations in leaves. Severe boron toxicity symptoms (BTS) were apparent only when leaf B concentrations exceeded 50 mol x 10⁻⁶ g⁻¹, but even at these high concentrations plant growth was only slightly reduced. E. camaldulensis showed least development of BTS, the lowest leaf B concentrations and least reduction in height growth due to B and NaCl. The results suggest that there was a correlation between both B tolerance and B accumulation in leaves and between tolerance to B and NaCl. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of ectomycorrhizal fungi on nitrogen mineralisation and the growth of Scots pine seedlings in natural peat

The aim of this study was to investigate the potential of different isolates of ectomycorrhizal (EM) fungi to enhance the growth of Pinus sylvestris seedlings in five natural peat substrates with different nitrogen concentrations, and the effect of the Scots pine seedlings and fungal inoculum on the formation of dissolved inorganic and organic nitrogen in peat. Utilization of different organic nitrogen compounds by microbial community in the peat was also investigated using Biolog MT MicroPlates. Inoculation of the seedlings with EM fungi enhanced seedling growth. Piloderma croceum increased root growth especially, whereas Lactarius rufus increased needle growth and Suillus variegatus I, II and III improved both root and needle growth. All the EM fungi also significantly affected stem growth. Nitrogen concentration of the peat did not affect seedling growth as much as the EM fungi. At the lowest peat N concentration (1.17%) NH ₄ ⁺ mineralisation was lower and DON (dissolved organic nitrogen) accumulation higher than at higher peat N concentrations. The EM fungal isolates had different effects on NH ₄ ⁺ and DON accumulation/degradation in peat. The EM fungal isolates significantly increased NH ₄ ⁺ formation in the peat, whereas L. rufus and P. croceum had an opposite effect on DON accumulation. S. variegatus I significantly decreased the DON concentrations during peat incubation. The N concentration of the peat slightly affected the utilization of amino acids and polyamines by the microbial community, whereas inoculation with S. variegatus I, II or III had no effect.     

Response of ectomycorrhizal fungi to benomyl and nocodazole: growth inhibition and microtubule depolymerization

The growth of seven ectomycorrhizal fungi was tested in the presence of the antimicrotubule drugs benomyl and nocodazole. The polymerization stage of the cytoplasmic microtubules in the hyphal cells was visualized by indirect immunofluorescence microscopy after a 3-h drug treatment. Nocodazole reduced the growth of all the fungi tested at concentrations of 2 and 4 g ml^-1 and caused strong depolymerization of microtubules in all other species except Hebeloma cylindrosporum. Benomyl inhibited the growth and depolymerized the microtubules in the ascomycete Cenococcum geophilum, while in the basidiomycetes it reduced the growth and depolymerized the microtubules only in H. cylindrosporum. The role of the microtubule cytoskeleton and the target of the benzimidazole-derived drugs in fungal cells are discussed.     

Nitrogen and phosphorus cycling in relation to stand age of Eucalyptus regnans F. Muell

Lupins, canola, ryegrass and wheat fertilized with Na₂ ³⁵SO₄ and either ¹⁵NH₄Cl or K¹⁵NO₃(N:S=10:1), were grown in the field in unconfined microplots, and the sources of N and S (fertilizer, soil, atmosphere, seed) in plant tops during crop development were estimated. Modelled estimates of the proportion of lupin N derived from the atmosphere, which were obtained independently of reference plants, were used to calculate the proportion of lupin N derived from the soil. Total uptake of N and S and uptake of labelled N and S increased during crop development. Total uptake of S by canola was higher than lupins, but labelled S uptake by lupins exceeded uptake by canola. The form of N applied had no effect on uptake of labelled and unlabelled forms of N or S. Ratios of labelled to unlabelled S and ratios of labelled to unlabelled N derived from soil sources decreased during growth, and were less for S than for N for each crop at each sampling time. Although ratios of labelled to unlabelled soil-derived N were similar between crops at 155, 176 and 190 days after sowing, ratios of labelled to unlabelled S for lupins were higher than for the reference crops and declined during this period. The ratios of labelled to unlabelled S in lupins and the reference plants therefore bore no relationship either to ratios of labelled to unlabelled soil-derived N in the plants, or to total S uptake by the plants. Therefore the hypothesis that equal ratios of labelled N to unlabelled soil-derived N in legumes (Rleg) and reference plants (Rref) would be indicated by equal ratios of labelled to unlabelled S was not supported by the data. The results therefore show that the accuracy of reference plant-derived values of Rleg cannot be evaluated by labelling with ³⁵S.     

Acclimation to temperature and temperature sensitivity of metabolism by ectomycorrhizal fungi

Ectomycorrhizal (ECM) fungi contribute significantly to ecosystem respiration, but little research has addressed the effect of temperature on ECM fungal respiration. Some plants have the ability to acclimate to temperature such that long‐term exposure to warmer conditions slows respiration at a given measurement temperature and long‐term exposure to cooler conditions increases respiration at a given measurement temperature. We examined acclimation to temperature and temperature sensitivity (Q₁₀) of respiration by ECM fungi by incubating them for a week at one of three temperatures and measuring respiration over a range of temperatures. Among the 12 ECM fungal isolates that were tested, Suillus intermedius, Cenococcum geophilum, and Lactarius cf. pubescens exhibited significant acclimation to temperature, exhibiting an average reduction in respiration of 20–45% when incubated at 23 °C compared with when incubated at 11 or 17 °C. The isolates differed significantly in their Q₁₀ values, which ranged from 1.67 to 2.56. We also found that half of the isolates significantly increased Q₁₀ with an increase in incubator temperature by an average of 15%. We conclude that substantial variation exists among ECM fungal isolates in their ability to acclimate to temperature and in their sensitivity to temperature. As soil temperatures increase, ECM fungi that acclimate may require less carbon from their host plants than fungi that do not acclimate. The ability of some ECM fungi to acclimate may partially ameliorate the anticipated positive feedback between soil respiration and temperature.     

Twig and foliar nutrient concentrations in relation to nitrogen and phosphorus supply in a eucalypt (Eucalyptus diversicolor F. Muell.) and an understorey legume (Bossiaea laidlawiana Tovey and Morris)

The sensitivity of tissue nutrient concentrations to changes in plant age and the supply of P and N was compared between leaves and associated twigs in two forest species. In a young regrowth stand, tissues were sampled on three occasions from the mid-crown position of karri (Eucalyptus diversicolor F. Muell.) and Bossiaea laidlawiana Tovey and Morris, a major understorey legume. Leaves and twigs were also sampled from young plants of B. laidlawiana growing in a mature eucalypt stand to which P treatments had been applied.Nitrogen application increased N concentrations in twigs of karri and B. laidlawiana, but not in leaves. Phosphorus application increased P concentrations in both leaves and twigs of karri but the average increases were proportionally greater in twigs (65%) than in leaves (36%). Over the sampling period, P concentrations in leaves declined, while those in twigs were relatively stable. In B. laidlawiana, P supply also had a larger effect on P concentrations in twigs than in leaves. Addition of 200 kg P ha^–1 increased average P concentrations in twigs by 109% in the regrowth stand and by 215% in the mature stand while the corresponding increases in leaves were only 11% and 27%. Concentrations of other nutrients in both species were also affected by N and P application, the most notable being a decline in the concentrations of the minor nutrients, Zn and Cu, with increased P supply.The increased N concentrations in twigs of karri, and the increased P concentrations in tissues of both species, were associated with responses of karri to added N and P, and of B. laidlawiana to added P. This indicates that tissue concentrations of N and P were generally below critical concentrations where N and P were not applied. The results show that for these species twigs may be a better tissue than leaves for diagnosing deficiencies or predicting N and P requirements. The ratio of P concentrations in twigs to P concentrations in leaves also increased with added P. It is suggested that this ratio may be a useful index if it reduces the variability caused by sampling position within the crown or genetic differences between plants.     

Daily stem growth patterns in irrigated Eucalyptus globulus and E. nitens in relation to climate

Daily increments in stem radius were determined from hourly dendrometer measurements in each of three irrigated Eucalyptus nitens and E. globulus trees. Multiple regressions determined from daily weather variables accounted for 40–50% of the variance in increment. The use of weather variables lagged by 1–2 days increased the variance explained. The diurnal variation in stem radius was resolved into three mathematically defined phases: shrinkage, recovery and increment. The positive daily net increment in stem radius, by definition, occurred in the increment phase. Average weather conditions during this phase (predominantly night-time) did not explain any more variance in increment than the average daily conditions, determined over a 24 h period. Daily increment was resolved into a rate of stem radius increase during the increment phase and the duration (hours) of that phase. Significant species by month interactions were evident with growth in summer characterised by faster rates of stem expansion over shorter time periods within each diurnal cycle. E. nitens tended to have longer increment phases in spring and autumn, and faster phase rates in autumn than E. globulus. Interactions between weather variables and cambial growth were complicated and varied over the year. The correlation between temperature and stem growth varied from positive in spring to zero or negative during summer. The data indicate a need to understand weather-by- climate interactions at the level of whole tree physiology in order to fully understand the effect of weather on cambial activity and therefore stem increment and wood properties. Received: 12 April 1999 / Accepted: 6 July 1999     

Fungal hypaphorine reduces growth and induces cytosolic calcium increase in root hairs of Eucalyptus globulus

Summary. Root hairs are tubular cells resulting from a tip-localized growth in which calcium ions play a key role. Hypaphorine, an indole alkaloid secreted by the fungus Pisolithus microcarpus during the formation of ectomycorrhizae with the host plant Eucalyptus globulus, inhibits root hair tip growth. Hypaphorine-induced inhibition is linked to a transient depolarization of the plasma membrane and a reorganization of the actin and microtubule cytoskeletons. Here we investigated the activity of hypaphorine on calcium distribution in E. globulus root hairs with the ratiometric fluorochrome calcium indicator Indo-1. In 85% of actively growing root hairs, a significant but modest calcium gradient between the apex and the base was observed due to an elevated cytoplasmic calcium concentration at the apical tip. Following exposure to 1 mM hypaphorine, the apical and basal cytoplasmic Ca²⁺ concentration increased in 70 and 77% of the hairs, respectively, 10 min after treatment. This led to a reduced calcium gradient in 81% of the cells. The hypothetical links between calcium concentration elevation, regulation of actin cytoskeleton dynamics, and root hair growth inhibition in response to hypaphorine treatment are discussed. Correspondence and reprints: UMR 1136 Interactions Arbres–Microorganismes, Faculté des Sciences, Université Nancy I, BP 239, 54506 Vandoeuvre Cedex, France.     

Seed phosphorus (P) content affects growth,and P uptake of wheat plants and their association with arbuscular mycorrhizal (AM) fungi

Two experiments were carried out in a growth chamber and a naturally lit glasshouse to investigate the influence of seed phosphorus (P) reserves on growth and P uptake by wheat plants (Triticum aestivum cv Krichauff), and their association with arbuscular mycorrhizal (AM) fungi. Increased seed P reserves improved plant growth at a range of P supply up to over 100 mg P kg^–1 soil. Plants grown from seeds with high P reserves tended to accumulate more P from soil, which was mainly attributed to better root system development. Mycorrhizal colonisation did not significantly affect P uptake of plants grown with low irradiance (in growth chamber). However, in the naturally lit glasshouse, mycorrhizal plants had significantly higher P concentrations than non-mycorrhizal plants. Furthermore, mycorrhizal plants grown from seeds low in P accumulated similar amounts of P compared with those grown from seeds with high P, indicating that mycorrhizal colonisation may overcome the disadvantage of having low seed P reserves in the field.     

Organic anion exudation by ectomycorrhizal fungi and Pinus sylvestris in response to nutrient deficiencies

Low molecular weight organic anions (LMWOA) can enhance weathering of mineral grains. We tested the hypothesis that ectomycorrhizal (EcM) fungi and tree seedlings increase their exudation of LMWOA when supply of magnesium, potassium and phosphorus is low to enhance the mobilization of Mg, K and P from mineral grains. Ectomycorrhizal fungi and Pinus sylvestris seedlings were cultured in symbiosis and in isolation on glass beads with nutrient solution or with sand as a rooting medium, with a complete nutrient supply or with Mg, K, P or N in low supply. Concentrations of all dicarboxylic LMWOA in the rooting medium were measured. Nonmycorrhizal seedlings released predominantly malonate. Colonization with Hebeloma longicaudum decreased the amount of organic anions exuded, whereas Paxillus involutus and Piloderma croceum increased the concentration of oxalate but not the total amount of LMWOA. Phosphorus deficiency increased the concentration of LMWOA by nonmycorrhizal and EcM seedlings. Magnesium deficiency increased the concentration of oxalate by nonmycorrhizal and EcM seedlings, but not the concentration of total LMWOA. Paxillus involutus grown in pure culture responded differently to low nutrient supply compared with symbiotic growth. Ectomycorrhizal fungi did not increase the total concentration of LMWOA compared with nonmycorrhizal seedlings but, depending on the fungal species, they affected the type of LMWOA found.