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.     

The improvement of plant N acquisition from an ammonium-treated,drought-stressed soil by the fungal symbiont in arbuscular mycorrhizae

The ability of the external mycelium in arbuscular mycorrhiza for N uptake and transport was studied. The contribution of the fungal symbiont to N acquisition by plants was studied mainly under waterstressed conditions using ¹⁵N. Lettuce (Lactuca sativa L) was the host for two isolates of the arbuscular mycorrhizal fungi Glomus mosseae and G. fasciculatum. The experimental pots had two soil compartments separated by a fine mesh screen (60 m). The root system was restricted to one of these compartments, while the fungal mycelium was able to cross the screen and colonize the soil in the hyphal compartment. A trace amount of ¹⁵NH ₄ ⁺ was applied to the hyphal compartment 1 week before harvest. Under water-stressed conditions both endophytes increased the ¹⁵N enrichment of plant tissues; this was negligible in nonmycorrhizal control plants. This indicates a direct effect of arbuscular mycorrhizal fungi on N acquisition in relatively dry soils. G. mosseae had more effect on N uptake and G. fasciculatum on P uptake under the water-limited conditions tested, but both fungi improved plant biomass production relative to nonmycorrhizal plants to a similar extent.     

In vitro weathering of phlogopite by ectomycorrhizal fungi

Oxalate accumulation in external medium under hyphal mats of two ectomycorrhizal species is strongly stimulated (1.7 to 35 fold) by a simultaneous depletion of available K⁺ and Mg²⁺. Pisolithus tinctorius strain 441 accumulates oxalate both on NH₄–N and on NO₃–N whereas Paxillus involutus strain COU only accumulates oxalate on NO₃–N. On NO₃–N, under a simultaneous K⁺ and Mg²⁺ deficiency, P. involutus COU is a very active oxalate producer compared to P. tinctorius 441. The present results could explain the various mineralogical evolutions of a phlogopite mica previously recorded under P. involutus COU or P. tinctorius 441 and suggest a key role for fungal oxalic acid during mineral weathering in response to nutrient deficiency.     

Limited transfer of nitrogen between wood decomposing and ectomycorrhizal mycelia when studied in the field

Transfer of ¹⁵N between interacting mycelia of a wood-decomposing fungus (Hypholoma fasciculare) and an ectomycorrhizal fungus (Tomentellopsis submollis) was studied in a mature beech (Fagus sylvatica) forest. The amount of ¹⁵N transferred from the wood decomposer to the ectomycorrhizal fungus was compared to the amount of ¹⁵N released from the wood-decomposing mycelia into the soil solution as ¹⁵N-NH₄. The study was performed in peat-filled plastic containers placed in forest soil in the field. The wood-decomposing mycelium was growing from an inoculated wood piece and the ectomycorrhizal mycelium from an introduced root from a mature tree. The containers were harvested after 41 weeks when physical contact between the two foraging mycelia was established. At harvest, ¹⁵N content was analyzed in the peat (total N and ¹⁵NH₄ ⁺) and in the mycorrhizal roots. A limited amount of ¹⁵N was transferred to the ectomycorrhizal fungus and this transfer could be explained by ¹⁵NH₄ ⁺ released from the wood-decomposing fungus without involving any antagonistic interactions between the two mycelia. Using our approach, it was possible to study nutritional interactions between basidiomycete mycelia under field conditions and this and earlier studies suggest that the outcomes of such interactions are highly species-specific and depend on environmental conditions such as resource availability.     

Relationships between fungal uptake of ammonium, fungal growth and nitrogen availability in ectomycorrhizal Pinus sylvestris seedlings

 Nitrogen deposition and intentional forest fertilisation with nitrogen are known to affect the species composition of ectomycorrhizal fungal communities. To learn more about the mechanisms responsible for these effects, the relations between fungal growth, nitrogen uptake and nitrogen availability were studied in ectomycorrhizal fungi in axenic cultures and in symbiosis with pine seedlings. Effects of different levels of inorganic nitrogen (NH₄) on the mycelial growth of four isolates of Paxillus involutus and two isolates of Suillus bovinus were assessed. With pine seedlings, fungal uptake of ¹⁵N-labelled NH₄ was studied in short-term incubation experiments (72 h) in microcosms and in long-term incubation experiments (3 months) in pot cultures. For P. involutus growing in symbiosis with pine seedlings, isolates with higher NH₄ uptake were affected more negatively at high levels of nitrogen availability than isolates with lower uptake. More NH₄ was allocated to shoots of seedlings colonised by a high-uptake isolate, indicating transfer of a larger fraction of assimilated NH₄ to the host than with isolates showing lower NH₄ uptake rates. Thus low rates of N uptake and N transfer to the host may enable EM fungi avoid stress induced by elevated levels of nitrogen. Seedlings colonised by S. bovinus transferred a larger fraction of the ¹⁵N label to the shoots than seedlings colonised by P. involutus. Seedling shoot growth probably constituted a greater carbon sink in pot cultures than in microcosms, since the mycelial growth of P. involutus was more sensitive to high NH₄ in pots. There was no homology in mycelial growth rate between pure culture and growth in symbiosis, but N uptake in pure culture corresponded to that during growth in symbiosis. No relationship was found between deposition of antropogenic nitrogen at the sites of origin of the P. involutus isolates and their mycelial growth or uptake of inorganic nitrogen. Accepted: 18 September 1998     

Arginine bi-directional translocation and breakdown into ornithine along the arbuscular mycorrhizal mycelium

Bi-directional translocation and degradation of Arginine (Arg) along the arbuscular mycorrhizal (AM) fungal mycelium were testified through ¹⁵N and/or ¹³C isotopic labeling. In vitro mycorrhizas of Glomus intraradices and Ri T-DNA-transformed carrot roots were grown in dual compartment Petri dishes. [¹⁵N- and/or¹³C]Arg was supplied to either the fungal compartment or the mycorrhizal compartment or separate dishes containing the uncolonized roots. The levels and labeling of free amino acids (AAs) in the mycorrhizal roots and in the extraradical mycelia(ERM) were measured by gas chromatography/mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC). The ERM of AM fungi exposed in either NH₄ ⁺ or urea as sole external nitrogen source had much higher ¹⁵N enrichment of Arg, compared with those in nitrate or exogenous Arg; however, glycerol supplied as an external carbon source to the ERM had no significant effect on the level of Arg in the ERM. Meanwhile, Arg biosynthesized in the ERM could be translocated intact to the mycorrhizal roots and thereby the level of Arg in the mycorrhizal roots increased to about 20% after culture of ERM in 4 mmol/L NH₄ ⁺ for 6 weeks. Also Arg was found to be bi-directionally transported along the AM fungal mycelium through [U-¹³C]Arg labeling either in the mycorrhizal compartment or in the fungal compartment. Once Arg was translocated to the potential N-limited sites, it would be further degraded into ornithine (Orn) and urea since either [U-¹³C] or [U-¹⁵N/U-¹³C]Orn was apparently shown up in the mycorrhizal root tissues when [U-¹³C] or [U-¹⁵N/U-¹³C]Arg was labeled in the fungal compartment, respectively. Evidently Orn formation indicated the ongoing activities of Arg translocation and degradation through the urea cycle in AM fungal mycelium. Supported by Science and Technology Department of Zhejiang Province (Grant No. 2006C22009).     

Utilization of organic nitrogen at two different substrate pH by different ectomycorrhizal fungi growing in symbiosis with Pinus sylvestris seedlings

The aim of this study was to test the potential of four isolates of ectomycorrhizal (EM) fungi to utilize organic nitrogen (N) at two different substrate pHs. The organic N source (¹⁵N labelled lyophilised fungal mycelium) was mixed with either untreated peat/sand mixture (pH 4.9) or peat/sand mixture limed to a pH of 5.9 and put in cylindrical containers added to each pot. The content of the containers was separated from the roots of Pinus sylvestris seedlings by a nylon mesh and a 2 mm air gap to reduce diffusion of labelled N to the roots. The mycorrhizal plants (except those colonized by Suillus variegatus 2) took up significantly more ¹⁵N from the labelled mycelium than uncolonized seedlings. Liming significantly reduced the uptake of ¹⁵N by one of the EM fungi (unidentified) but not the other tested species (Paxillus involutus and two isolates of S. variegatus). The EM fungal isolates differed in their influence on the bacterial activity of the soil. This was reduced with P. involutus at both pH levels and increased with one of the two S. variegatus isolates at the high pH and with the other S. variegatus isolate at the low pH level. Liming the soil generally increased bacterial activity. The influence of liming on the proportion of organic N uptake in relation to inorganic N uptake by ectomycorrhizal trees is discussed.     

Competition for nitrogen between Pinus sylvestris and ectomycorrhizal fungi generates potential for negative feedback under elevated CO2

We investigated fungal species-specific responses of ectomycorrhizal (ECM) Scots pine (Pinus sylvestris) seedlings on growth and nutrient acquisition together with mycelial development under ambient and elevated CO₂. Each seedling was associated with one of the following ECM species: Hebeloma cylindrosporum, Laccaria bicolor, Suillus bovinus, S. luteus, Piloderma croceum, Paxillus involutus, Boletus badius, or non-mycorrhizal, under ambient, and elevated CO₂ (350 or 700 μl l⁻¹ CO₂); each treatment contained six replicates. The trial lasted 156 days. During the final 28 days, the seedlings were labeled with ¹⁴CO₂. We measured hyphal length, plant biomass, ¹⁴C allocation, and plant nitrogen and phosphorus concentration. Almost all parameters were significantly affected by fungal species and/or CO₂. There were very few significant interactions. Elevated CO₂ decreased shoot-to-root ratio, most strongly so in species with the largest extraradical mycelium. Under elevated CO₂, ECM root growth increased significantly more than hyphal growth. Extraradical hyphal length was significantly negatively correlated with shoot biomass, shoot N content, and total plant N uptake. Root dry weight was significantly negatively correlated with root N and P concentration. Fungal sink strength for N strongly affected plant growth through N immobilization. Mycorrhizal fungal-induced progressive nitrogen limitation (PNL) has the potential to generate negative feedback with plant growth under elevated CO₂. Responsible Editor: Herbert Johannes Kronzucker     

Uptake and transport of organic and inorganic nitrogen by arbuscular mycorrhizal fungi

New information on N uptake and transport of inorganic and organic N in arbuscular mycorrhizal fungi is reviewed here. Hyphae of the arbuscular mycorrhizal fungus Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe (BEG 107) were shown to transport N supplied as ¹⁵N-Gly to wheat plants after a 48 h labelling period in semi-hydroponic (Perlite), non-sterile, compartmentalised pot cultures. Of the ¹⁵N supplied to hyphae in pot cultures over 48 h, 0.2 and 6% was transported to plants supplied with insufficient N or sufficient N, respectively. The increased ¹⁵N uptake at the higher N supply was related to the higher hyphal length density at the higher N supply. These findings were supported by results from in vitro and monoxenic studies. Excised hyphae from four Glomus isolates (BEG 84, 107, 108 and 110) acquired N from both inorganic (¹⁵NH₄ ¹⁵NO₃, ¹⁵NO₃ ⁻ or ¹⁵NH₄ ⁺) and organic (¹⁵N-Gly and ¹⁵N-Glu, except in BEG 84 where amino acid uptake was not tested) sources in vitro during short-term experiments. Confirming these studies under sterile conditions where no bacterial mineralisation of organic N occurred, monoxenic cultures of Glomus intraradices Schenk and Smith were shown to transport N from organic sources (¹⁵N-Gly and ¹⁵N-Glu) to Ri T-DNA transformed, AM-colonised carrot roots in a long-term experiment. The higher N uptake (also from organic N) by isolates from nutrient poor sites (BEG 108 and 110) compared to that from a conventional agricultural field implied that ecotypic differences occur. Although the arbuscular mycorrhizal isolates used contributed to the acquisition of N from both inorganic and organic sources by the host plants/roots used, this was not enough to increase the N nutritional status of the mycorrhizal compared to non-mycorrhizal hosts. This revised version was published online in June 2006 with corrections to the Cover Date.     

Protein synthesis inPinus resinosa and the ectomycorrhizal fungusPaxillus involutus prior to ectomycorrhiza formation

Summary Seedlings of Pinus resinosa Ait. in test tubes were inoculated with the ectomycorrhizal fungus Paxillus involutus Fr. or with discs of sterile modified Melin-Norkrans (MMN) medium. Paxillus involutus was also inoculated to control tubes in the absence of Pinus resinosa seedlings. In vivo labelling of proteins in Pinus resinosa roots and in Paxillus involutus mycelium was carried out using ³⁵S l-methionine 1, 2, 3, 4, 5 and 7 days after inoculation. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDSPAGE) of the protein extracts from the four treatments and autoradiography demonstrated that the presence of root exudates altered protein synthesis in Paxillus involutus as three major bands disappeared when Paxillus involutus was exposed to root exudates. Protein synthesis in Pinus resinosa was also altered when Paxillus involutus was introduced into the tubes, since at least two bands were more intense when seedlings were inoculated with Paxillus involutus, as compared to control roots. No difference was observed in the growth and the label incorporation of Paxillus involutus growing with or without root exudates. Ectomycorrhizal roots were not formed during this experiment. Gene regulation in this ectomycorrhizal association occurs, therefore, prior to the formation of ectomycorrhizal roots.     

Nitrogen amendments reduce the growth of extramatrical ectomycorrhizal mycelium

The effect of three different nitrogen sources on the growth of external ectomycorrhizal mycelium was studied in Perspex micorocosms. Nonsterile peat was used as substrate. Five different fungal isolates growing in symbiosis with pine seedlings were investigated: two isolates of Paxillus involutus, one of Suillus bovinus and two unidentified ectomycorrhizal fungi isolated from ectomycorrhizal root tips. Three different nitrogen sources were used: ammonium as (NH₄)₂SO₄, nitrate as NaNO₃ and a complete nutrient solution (Ingestad 1979), and three different nitrogen concentrations, 1, 2 or 4 mg N/g dry wt. of peat. The mycelial growth of all fungi was found to be negatively affected by the nitrogen amendments, although the sensitivity to nitrogen varied between the isolates. One of the unidentified isolates was extremely sensitive and growth was completely inhibited by all nitrogen treatments. In contrast, the growth of one of the P. involutus isolates was only slightly reduced by the nitrogen amendments. The different nitrogen sources all reduced growth, and since no significant difference was found between the nitrogen sources or between the different nitrogen concentrations the results were pooled to give one value that summarized the effect of nitrogen on mycelial growth. Thus, the mycelial growth of one of the two P. involutus isolates was reduced to approximately 80% of the growth in the control, the other P. involutus and one of the unidentified fungi, vgk 2 89.10, were reduced to 40–50% of the control growth, S. bovinus to 30% of the control and the most sensitive fungus, the unidentified isolate vg 1 87.10, was reduced to 3% of the growth in the control treatment. In all experiments, the shoot to root ratio generally increased, mainly as a result of increased shoot growth.     

Effects of inorganic nitrogen and phosphorus supply on nitrogen aquisition from alanine by birch seedlings in symbiosis with Paxillus involutus

Northern forests are exposed to relatively high ammonia inputs due to high atmospheric deposition and the common practise of forest fertilization. It is not known how increased soil NH₄ ⁺concentrations affect acquisition of symbiosis-mediated N from organic sources. We examined the effect of inorganic N and P availability on N acquisition from alanine by 43 weeks old birch (Betula pendula) seedlings in symbiosis with the ectomycorrhizal fungus Paxillus involutus. The seedlings were exposed for 9 weeks to nutrient additions equivalent to 43 kg N and 6.4 kg P ha^-1 (low N and P availability), 250 kg N and 38 kg P ha^-1(high N and P availability) or to 250 kg N and 6.4 kg P ha^-1 (high N and low P availability). Carbon and nitrogen allocation between the symbionts was assessed by exposing the foliage to ¹⁴CO₂ and the mycelium to ¹⁵N-alanine or ¹⁵NH₄ ⁺ simultaneously and measuring the distribution of the isotopic tracers after a three-day chase period. High inorganic N combined with low P availability did not have marked effect on symbiosis-mediated N uptake from alanine, whilst high N and P availability reduced alanine-derived ¹⁵N translocation by the fungus to the plant. Shoot ¹⁵N concentration and concentration of ¹⁴C in the extramatrical mycelium correlated significantly across treatments pointing to controlled reciprocity of transactions between the partners.     

Boron uptake by ectomycorrhizas of silver birch

Boron (B) is an essential micronutrient for plants but it is thought not to be essential for fungi. We studied whether the extraradical mycelia of Paxillus involutus in symbiosis with silver birch (Betula pendula) take up B and transport it to the host plant. We grew mycorrhizal plants in flat microcosms with a partitioning wall, below which there was only extraradical mycelium. A boric acid solution enriched in ¹⁰B was applied to these mycelia. Increased ¹⁰B/¹¹B isotope ratios were subsequently measured in birch leaves, stems, and roots plus mycorrhizas in the upper compartment. Boron was therefore taken up by the mycorrhizal mycelia and transported to the host plant in this species combination.     

Hyphal N transport by a vesicular-arbuscular mycorrhizal fungus associated with cucumber grown at three nitrogen levels

Cucumis sativus L. cv. Aminex (F1 hybrid) was grown alone or in symbiosis with Glomus intraradices Schenck and Smith in containers with two hyphal compartments (HC_A and HC_B) on either side of a root compartment (RC) separated by fine nylon mesh. Plants received a total of either 100, 200 or 400 mg N which were applied gradually to the RC during the experiment. ¹⁵N was supplied to HC_A 42 d after plating, at 50 mg ¹⁵NH₄ ⁺-N kg^–1 soil. Lateral movement of the applied ¹⁵N towards the roots was minimized by using a nitrification inhibitor and a hyphal buffer compartment.Non-mycorrhizal controls contained only traces of ¹⁵N after a 27 d labelling period irrespective of the amount of N supplied to the RC. In contrast, 49, 48 and 27% of the applied ¹⁵N was recovered in mycorrhizal plants supplied with 100, 200 and 400 mg N, respectively. The plant dry weight was increased by mycorrhizal colonization at all three levels of N supply, but this effect was strongest in plants of low N status. The results indicated that this increase was due partly to the improved inflow of N via the external hyphae. Root colonization by G. intraradices was unaffected by the amount of N supplied to the RC, while hyphal length increased in HC_A compared to HC_B. Although a considerable ¹⁵N content was detected in mycorrhizal roots adjacent to HC_B, only insignificant amounts of ¹⁵N were found in the external hyphae in HC_B. The external hyphae depleted the soil of inorganic N in both HC_A and HC_B, while the concentration of soil mineral N was still high in non-mycorrhizal containers at harvest. An exception was plants supplied with 400 mg N, where some inorganic N was present at 5 cm distance from the RC in HC_A. The possibility of a regulation mechanism for hyphal transport of N is discussed.     

Mycorrhizal Networks Interacting with Litter Improves Nutrients and Growth for One Plant through the Vary of N/P Ratio under Karst Soil

Arbuscular mycorrhizae (AM) fungi affect nutrient uptake for host plants, while it is unclear how AM fungi interacting with soil litter affect plant growth and nutrient utilization through mycorrhizal networks in karst soil of deficient nutrients beyond the rhizosphere. An experiment was conducted in a microcosm composed of a planting compartment for Cinnamomum camphora seedlings with or without Glomus mosseae fungus (M⁺ vs. M⁻ ) and an adjacent litter compartment containing or not containing additional litter material of Arthraxon hispidus (L⁺ vs. L⁻ ), where the compartments are connected either by nylon mesh of 20 μm or 0.45 μm which either allow available mycorrhizal networks within the litter compartment or prevent mycelium entering into the litter compartment (N⁺ vs. N⁻ ). Plant biomass and nutrients were measured. The results showed that the addition of litter changed the symbiotic process in mycorrhizal colonization, spore, and hyphal density, which when in association with the host plant then affected the biomass, and accumulations of N (nitrogen) and P (phosphorus) in the individual plant as well as root, stem, and leaf respectively. AM fungi increased N and P accumulations and N/P ratio in individual plants and plant tissues. A decrease of the N/P ratio of the individual plant was observed when AM fungus interacted significantly with litter through mycorrhizal networks in the litter compartment. The results indicate that the C. camphora seedlings benefited from litter in nutrient utilization of N and P through the vary of N/P ratio when accessing mycorrhizal networks. These findings suggest that mycorrhizal networks interacting with litter improve growth and nutrients of N and P for plants through the vary of N/P ratio in order to alleviate nutrient limitation under karst soil.     

Segregation of nitrogen use between ammonium and nitrate of ectomycorrhizas and beech trees

Here, we characterized nitrogen (N) uptake of beech (Fagus sylvatica) and their associated ectomycorrhizal (EM) communities from NH₄⁺ and NO₃^?. We hypothesized that a proportional fraction of ectomycorrhizal N uptake is transferred to the host, thereby resulting in the same uptake patterns of plants and their associated mycorrhizal communities. ¹⁵N uptake was studied under various field conditions after short‐term and long‐term exposure to a pulse of equimolar NH₄⁺ and NO₃^? concentrations, where one compound was replaced by ¹⁵N. In native EM assemblages, long‐term and short‐term ¹⁵N uptake from NH₄⁺ was higher than that from NO₃^?, regardless of season, water availability and site exposure, whereas in beech long‐term ¹⁵N uptake from NO₃^? was higher than that from NH₄⁺. The transfer rates from the EM to beech were lower for ¹⁵N from NH₄⁺ than from NO₃^?. ¹⁵N content in EM was correlated with ¹⁵N uptake of the host for ¹⁵NH₄⁺, but not for ¹⁵NO₃^?‐derived N. These findings suggest stronger control of the EM assemblage on N provision to the host from NH₄⁺ than from NO₃^?. Different host and EM accumulation patterns for inorganic N will result in complementary resource use, which might be advantageous in forest ecosystems with limited N availability.     

Role of nutrient level and defoliation on symbiotic function: experimental evidence by tracing 14C/15N exchange in mycorrhizal birch seedlings

High nutrient availability and defoliation generally reduce ectomycorrhizal colonization levels in trees, but it is not known how this affects the functional aspects of mycorrhizal symbiosis. It was therefore investigated whether (1) defoliation or increasing substrate N availability reduce C allocation from the plant to the fungus and N allocation from the fungus to the plant (symbiotic resource exchange), (2) symbiotic resource exchange depends on relative N and P availability, and (3) fungal N translocation to plant and plant C allocation to fungus are interdependent. Birch (Betula pendula) seedlings were grown in symbiosis with the ectomycorrhizal fungus Paxillus involutus at five times excess N, or at five times excess N and P for 6 weeks. One-half of the plants were defoliated and the plant shoots were allowed to photosynthesize ¹⁴CO₂ while the fungal compartment was exposed to ¹⁴NH₄. After 3 days, the ¹⁴C of plant origin in fungal tissues and ¹⁵N of fungal origin in plant tissues were quantified. Nutrient availability had no observable effect on symbiotic resource exchange in non-defoliated systems. Defoliation reduced symbiotic N acquisition by plants at all levels of nutrient availability, with the reduction being most marked at higher N availability, indicating an increased tendency in the symbiotic system to discontinue resource exchange after defoliation at higher fertility levels. The concentration of ¹⁴C in extramatrical mycelium correlated significantly with the concentration of ¹⁵N in birch shoots. The results support the assumption that N delivery to the host by the mycorrhizal fungus is dependent on C flow from the plant to the fungus, and that exchanges between the partners are reciprocal. No significant reductions in root ¹⁴C content as a response to defoliation were observed, indicating that defoliation specifically reduced allocation to fungus, but not markedly to roots.     

丛枝菌根真菌和施加不同形态氮肥对杉木幼苗养分吸收的影响

为了解丛枝菌根真菌(AMF)和不同形态氮对杉木(Cunninghamia lanceolata)生长和养分吸收的影响,以1 a生杉木幼苗接种摩西球囊霉(Glomus mosseae)和添加不同形态氮(NH₄⁺-N和NO₃^–-N),对其养分元素和生长状况的变化进行研究。结果表明,AMF显著提高了杉木的苗高和生物量,促进了杉木对N、P、K、Ca、Mg、Fe和Na的吸收,AMF对微量元素Fe、Na的促进作用总体上要强于大量元素K、Ca。与NO₃^–-N相比,AMF显著提高了NH₄⁺-N处理杉木的生物量、总C和N、Ca、Mg、Mn含量,而且这种显著性在叶中普遍高于根和茎。接种AMF可以促进杉木幼苗的生长和对养分元素的吸收,且添加NH₄⁺-N处理的促进作用要强于NO₃^–-N。     

Influence of ectomycorrhizal fungi on the response of Sitka spruce and Japanese larch to forms of phosphorus

Ectomycorrhizal fungi (Paxillus involutus, Suillus grevillei and two unidentified basidiomycetes from excised Sitka spruce mycorrhizas) were isolated from stands of Sitka spruce either in monoculture or in a mixture with Japanese larch in an Irish conifer plantation. The growth of these fungi and their mycorrhizal formation in Sitka spruce and Japanese larch were examined after incubation in modified Melin-Norkrans medium containing either KH₂PO₄, Ca₃(PO₄)₂ or Fe phytate as the phosphorus (P) source. P. involutus and S. grevillei utilized all three P sources. The unidentified basidiomycetes had limited ability to utilize Fe phytate. Basidiomycete 1 showed poor growth on KH₂PO₄ whereas growth of basidiomycete 2 was low on Ca₃(PO₄)₂. Pure culture synthesis studies confirmed that P. involutus and the two basidiomycetes formed mycorrhizas with both tree species but S. grevillei was mycorrhizal only on Japanese larch. P. involutus formed more mycorrhizas in both conifers than the other fungi. Following inoculation with each of the four fungi, shoot and root dry mass of both Sitka spruce and Japanese larch seedlings was enhanced compared with uninoculated/nonmycorrhizal controls. On Fe phytate, Paxillus-inoculated Sitka spruce seedlings had the lowest primary root length and on KH₂PO₄, Suillus-inoculated Japanese larch had the greatest number of short roots. The only differences when Sitka spruce seedlings were grown in either monoculture or in a mixture with Japanese larch mycorrhizal with S. grevillei were primary root length and number of short roots after growth on media containing Fe phytate.     

Degradation of 14C-labelled lignin and dehydropolymer of coniferyl alcohol by ericoid and ectomycorrhizal fungi

The ability of ericoid and ectomycorrhizal fungi to utilize ¹⁴C-labelled lignin and O¹⁴CH₃-labelled dehydropolymer of coniferyl alcohol as sole C sources has been assessed in pure culture studies. The results indicate that ericoid mycorrhizal fungi are more effective in degrading lignin than ectomycorrhizal fungi. Amongst the ectomycorrhizal fungi the facultative mycorrhizal fungus Paxillus involutus degraded lignin more readily than those which are normally considered to be obligately mycorrhizal fungi such as Suillus bovinus and Rhizopogon roseolus. The importance of these lignin degrading capabilities is discussed in relation to the predominance of specific mycorrhiza forms along a gradient of increasing organic matter and hence lignin content of soil.