The effect of pH on the growth of saprotrophic and ectomycorrhizal ammonia fungi in vitro

Some saprotrophic and ectomycorrhizal fungi produce reproductive structures, preferably in slightly alkaline to neutral forest soil. This research examines the growth of these "ammonia fungi" in liquid medium at various pH values. In the first experiment, the capacity of six buffers was examined to select appropriate buffers for stabilizing pH in the neutral-to-alkaline range by culture of three species of the ammonia fungi in media initially adjusted to pH 7, 8 or 9. The highest buffering capacity was shown in 2-(N-morpholino) ethanesulfonic acid (MES) at pH 7, and N, N-bis (2-hydroxyethyl) glycine (Bicine) and N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) at pH 8 and 9. In the second experiment, the growth of 15 strains of both saprotrophic and ectomycorrhizal ammonia fungi was tested on the medium initially adjusted to pH 3, 4, 5, 6 or 7 with MES, or to pH 8 or 9 buffered with Bicine. Many of the saprotrophic species grew well at pH 7 or 8; the ectomycorrhizal species showed optimum growth at pH 5 or 6. The pH suitable for the in vitro growth of these fungi was correlated with the pH of forest soil where these fungi occur.     

Influence of autoclaved saprotrophic fungal mycelia on proteolytic activity in ectomycorrhizal fungi

The production of proteolytic enzymes by several strains of ectomycorrhizal fungi i.e., Amanita muscaria (16-3), Laccaria laccata (9-12), L. laccata (9-1), Suillus bovinus (15-4), Suillus bovinus (15-3), Suillus luteus (14-7) on mycelia of Trichoderma harzianum, Trichoderma virens and Mucor hiemalis and sodium caseinate, yeast extract was evaluated. The strains of A. muscaria (16-3) and L. laccata (9-12) were characterized by the highest activity of the acidic and neutral proteases. Taking the mycelia of saprotrophic fungi into consideration, the mycelium of M. hiemalis was the best inductor for proteolytic activity. The examined ectomycorrhizal fungi exhibited higher activity of acidic proteases than neutral ones on the mycelia of saprotrophic fungi, which may imply the participation of acidic proteases in nutrition.     

Boron and other elements in sporophores of ectomycorrhizal and saprotrophic fungi

Fungi are usually thought not to have a boron (B) requirement. It is not known if mycorrhizas take up B from low concentrations that are common in forest soils, as fungi might also immobilise B. Here, we studied the B concentrations in sporophores of 49 ectomycorrhizal and 10 saprotrophic fungi to assess whether B is translocated in mycelium or not. Additionally, P and metal concentrations were measured for comparison. Variability both within species and between species was very large, as the lowest measured B concentration was 0.01 mg kg⁻¹ in Amanita muscaria, and the highest was 280 mg kg⁻¹ in Paxillus involutus. There was no clear difference between saprotrophic and mycorrhizal fungi. The majority of species did not accumulate B at more than 0.01–3 mg kg⁻¹, but there were some species that consistently had median concentration values higher than 5–6 mg kg⁻¹ and much higher maximum values, particularly Paxillus involutus, Lactarius necator and several Russula species. Most species increased their B concentration in B fertilised plots, but there were exceptions, particularly Rozites caperatus and Lactarius camphoratus. Boron concentrations did not correlate with those of other elements. In conclusion, B is translocated in the mycelia of most of the studied species. The differences between species may be due to differences in their water use, or carbohydrates used in translocation. It remains to be studied, if B concentrations in mycorrhizas or mycelia in soil are in the same order of magnitude as the larger ones found here, and if this has any effects on the host plants.     

Effect of competitive interactions between ectomycorrhizal and saprotrophic fungi on Castanea sativa performance

In Northeast of Portugal, the macrofungal community associated to chestnut tree (Castanea sativa Mill.) is rich and diversified. Among fungal species, the ectomycorrhizal Pisolithus tinctorius and the saprotroph Hypholoma fasciculare are common in this habitat. The aim of the present work was to assess the effect of the interaction between both fungi on growth, nutritional status, and physiology of C. sativa seedlings. In pot experiments, C. sativa seedlings were inoculated with P. tinctorius and H. fasciculare individually or in combination. Inoculation with P. tinctorius stimulated the plant growth and resulted in increased foliar-N, foliar-P, and photosynthetic pigment contents. These effects were suppressed when H. fasciculare was simultaneously applied with P. tinctorius. This result could be related to the inhibition of ectomycorrhizal fungus root colonization as a result of antagonism or to the competition for nutrient sources. If chestnut seedlings have been previously inoculated with P. tinctorius, the subsequent inoculation of H. fasciculare 30 days later did not affect root colonization, and mycorrhization benefits were observed. This work confirms an antagonistic interaction between ectomycorrhizal and saprotrophic fungi with consequences on the ectomycorrhizal host physiology. Although P. tinctorius is effective in promoting growth of host trees by establishing mycorrhizae, in the presence of other fungi, it may not always be able to interact with host roots due to an inability to compete with certain fungi.     

The impact of polyphenolic compounds on the in vitro growth of oak-associated foliar endophytic and saprotrophic fungi

Foliar fungal endophytes are horizontally transmitted symbionts that inhabit healthy, photosynthetic tissues of all lineages of land plants where they influence plant health and productivity. Endophyte communities often are more similar among closely related hosts, potentially as a result of a preference for particular morphological, ecophysiological, or chemical host traits. However, the various ecological and evolutionary factors that drive community assembly often are difficult to disentangle. Here, we examined the impact of six polyphenolic compounds on the growth of 15 phylogenetically diverse Quercus (oak)-associated fungal species and assessed whether tolerance to phenolics is associated with their degree of specialization to oaks in nature. Despite frequently reported antifungal properties of phenolics, we found that oak-associated fungi grew the same or better than positive controls in 78% of trials with all compounds, although fungal sensitivity differed as a function of compound type and concentration. Overall, species with high specificity to Quercus had the greatest tolerance to phenolics, whereas generalists were more sensitive. Differences between generalists and specialists suggest that variation in phenolic abundance and composition among oaks may act as a selective filter that influences endophyte host associations in nature.     

Chemical constituents of the bark of Endlicheria oreocola (Lauraceae) from Colombia

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Insights into nitrogen and carbon dynamics of ectomycorrhizal and saprotrophic fungi from isotopic evidence

The successful use of natural abundances of carbon (C) and nitrogen (N) isotopes in the study of ecosystem dynamics suggests that isotopic measurements could yield new insights into the role of fungi in nitrogen and carbon cycling. Sporocarps of mycorrhizal and saprotrophic fungi, vegetation, and soils were collected in young, deciduous-dominated sites and older, coniferous-dominated sites along a successional sequence at Glacier Bay National Park, Alaska. Mycorrhizal fungi had consistently higher δ¹⁵N and lower δ¹³C values than saprotrophic fungi. Foliar δ¹³C values were always isotopically depleted relative to both fungal types. Foliar δ¹⁵N values were usually, but not always, more depleted than those in saprotrophic fungi, and were consistently more depleted than in mycorrhizal fungi. We hypothesize that an apparent isotopic fractionation by mycorrhizal fungi during the transfer of nitrogen to plants may be attributed to enzymatic reactions within the fungi producing isotopically depleted amino acids, which are subsequently passed on to plant symbionts. An increasing difference between soil mineral nitrogen δ¹⁵N and foliar δ¹⁵N in later succession might therefore be a consequence of greater reliance on mycorrhizal symbionts for nitrogen supply under nitrogen-limited conditions. Carbon signatures of mycorrhizal fungi may be more enriched than those of foliage because the fungi use isotopically enriched photosynthate such as simple sugars, in contrast to the mixture of compounds present in leaves. In addition, some ¹³C fractionation may occur during transport processes from leaves to roots, and during fungal chitin biosynthesis. Stable isotopes have the potential to help clarify the role of fungi in ecosystem processes. Received: 7 January 1998 / Accepted: 9 November 1998     

Colonizing success of saprotrophic and ectomycorrhizal basidiomycetes on islands

The biodiversity of saprotrophic and ectomycorrhizal basidiomycetous macrofungi growing on seven islands in central Japan were compared to examine colonizing success within the context of island biogeography theory. Two hypotheses were tested: that the number of the fungal species depends on island area and that the slope of the species-area curve for saprotrophic and ectomycorrhizal macrofungi differ in response to differences in their nutritional requirements. Data for the number of species that were identified based on sporocarps closely fit the conventional species-area curve. The slopes of the species-area curve for saprotrophic fungi (0.316) and ectomycorrhizal fungi (0.469) were similar to those reported for insects and birds, and plants on other archipelagos, respectively. In addition species-area curve data showed that ectomycorrhizal fungi colonized only islands > 630 m(2). While the species composition of saprotrophic fungi found on any pair of islands was positively correlated to the ratio of the areas of the island pair being compared (smaller/larger), no such relationship was observed for ectomycorrhizal fungi. Conversely similar ectomycorrhizal fungi, mostly those belonging to the genera Amanita, Inocybe, Boletellus and Russula, were found on pairs of islands with similar vegetation in the same geographic region. These results suggested that the colonizing success by ectomycorrhizal fungi is limited by host plant diversity, which is lower on smaller islands, instead of restricted immigration resulting from limited spore dispersal ability.     

丛枝菌根真菌对三叶草根系分泌的有机酸组分和含量的影响

比较洗根法、层析纸法和琼脂膜法收集土培条件下生长的菌根化和非菌根化三叶草根分泌物的效果。试验采用三室根箱装置 ,将根系与菌丝生长空间分开 ,三叶草生长 5 6d后 ,打开三室根箱装置 ,由于尼龙网的阻挡作用使根系均匀垫积在尼龙网内侧并形成根垫。分别采用洗根法、层析纸法和琼脂膜法 3种方法收集三叶草根系分泌物 ,并通过高效液相色谱方法测定分泌物中草酸、酒石酸、苹果酸、乳酸、乙酸、顺丁烯二酸、反丁烯二酸、柠檬酸、丁二酸等有机酸的含量。结果表明 :3种收集方法收集的三叶草分泌的有机酸无论在种类上还是在数量上都存在相当大的差别。从检测到的有机酸种类来看 ,琼脂膜法收集检测到苹果酸、乙酸、顺丁烯二酸、柠檬酸、丁二酸和乳酸 6种有机酸 ;洗根法收集的分泌物检测到酒石酸、苹果酸、乙酸、顺丁烯二酸、柠檬酸、丁二酸和乳酸 7种有机酸 ;层析纸法收集的分泌物检测到酒石酸、苹果酸、柠檬酸和乳酸 4种有机酸。从收集到的有机酸数量来看 ,洗根法收集到的有机酸总量为 2 9.97～ 2 32 .7μg/( gfw· 2 h) ;琼脂膜法集到的有机酸总量为 1 .5～ 7.3μg/( cm2· 2 h) ;层析纸法收集的有机酸总量为0 .2 3～ 6.5 8μg/( cm2 · 2 h)。丛枝菌根真菌侵染对三叶草根系分泌的有机酸的组分和含量都有一     

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.     

Strategies of carbon and nitrogen acquisition by saprotrophic and ectomycorrhizal fungi in Finnish boreal Picea abies-dominated forests

We compared the δ¹³C and δ¹⁵N of forest material with an extensive sporocarp collection to elucidate the role of litter, wood and soil as fungal carbon and nitrogen sources in Finnish boreal Picea abies-dominated forests. Ectomycorrhizal Hydnum and Cortinarius had higher δ¹⁵N than other ectomycorrhizal fungi, suggesting use of ¹⁵N-enriched, deeper nitrogen. Russula had lower δ¹⁵N than other ectomycorrhizal fungi and resembled some litter decay genera, suggesting use of litter-derived nitrogen. There was little variation in δ¹⁵N among other genera of ectomycorrhizal fungi, indicating limited functional diversity in nitrogen use. Saprotrophic Leotia, Gymnopus, Hypholoma, Pholiota, Rhodocollybia and Calocera had δ¹⁵N values similar to ectomycorrhizal fungi, indicating overlap in use of older nitrogen from soil or roots or use of newly fixed nitrogen. Genera of litter and wood decay fungi varied up to 6‰ in δ¹³C and 10‰ in δ¹⁵N, suggesting large differences in carbon and nitrogen sources and processing. Similar δ¹³C between white and brown rot wood decay fungi also suggest that white rot fungi do not use lignin-derived carbon. Together, these δ¹³C and δ¹⁵N patterns of fungi from Finnish boreal forests enhance our knowledge of fungal functional diversity and indicate broad use of litter, wood and soil resources.     

红皮云杉外生菌根菌单接种及混合接种对苗木生长的影响

以提高外生菌根真菌对红皮云杉苗木促生长效果为目的,在前期研究的基础上,采用菌株配对培养的方法对获得的云杉外生菌根真菌进行混合接种菌株组合筛选;采用沟施菌剂方法,对3年生红皮云杉移床苗进行外生菌根菌菌株组合野外混合接种试验,同时以各菌株野外单接种作为对照,研究外生菌根真菌单接种及混合接种对红皮云杉苗木生长的影响。试验结果表明:供试菌株及菌株组合对红皮云杉苗木生长均有一定的促进作用。菌株L15促生长效果最佳,接种100d苗木高生长高于对照30.88%,地径高于对照15.29%。组合L15/025与L15/009促苗木生长效果低于单接种L15的效果,高于单接种009和025的效果。接种菌株010和组合L15/025的苗木与对照相比,叶绿素含量提高差异显著,叶绿素a水平分别高于对照59.15%、54.61%,叶绿素b水平分别高于对照76.34%和67.78%。除接种菌株010的苗木外,其他处理苗木其过氧化氢酶活性与对照相比均有所降低。所有处理苗木的根系活力均低于对照。综上,外生菌根菌高效菌株与一般菌株混合接种会弱化高效菌株自身接种效果;苗木过氧化氢酶活性、苗木根系活力与苗木的生物量间无相关性。     

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.Uninoculated plants had less than 5% of their fine root length colonized by ectomycorrhizal fungi. In contrast, inoculated plants had 30% or greater of their fine root length ectomycorrhizal. Inoculation increased the uptake of P and growth of plants for all isolates and at both levels of soil pH, although growth responses to inoculation were greater at pH 6, particularly for the two L. laccata isolates. Isolates which colonized roots most extensively increased plant growth to the greatest extent. D. maculata was the most effective fungal isolate at pH 5, and both D. maculata and L. laccata A were most effective at pH 6. The effects of soil pH on plant growth were also related to some extent to the effects of soil pH on colonized root length. Growth responses to inoculation were related less well to hyphal development in soil. The L. laccata isolates formed more hyphae in soil (on a per pot, per m of fine root, and per m of colonized fine root basis) than other fungal isolates, but were not always more effective in increasing plant grown.     

The effect of aluminium on phosphate uptake by three isolated ectomycorrhizal fungi

Three wheat cultivars with different tolerances against free aluminium were grown monoxenically in association with Azospirillum brasilense. In situ nitrogen fixation, measured with the acetylene reduction assay, was higher by the aluminium-tolerant cultivars than by the sensitive cultivar. The transfer of fixed nitrogen to the host plant, determined by the ¹⁵N dilution technique, was also significantly higher in the aluminium-resistant wheat plants. The total accumulation of fixed nitrogen in the host plants due to an A. brasilense inoculation varied from approximately 13% to 17% of the total nitrogen in the root and 2.9% to 3.9% of the nitrogen in the shoot.The quantity and quality of exudates released in liquid nutrient solution were analysed separately for two of the wheat cultivars, one aluminium-tolerant and one aluminium-sensitive. After 29 days of growth the aluminium-tolerant plants exudated significantly higher total amounts of carbon than aluminium-sensitive plants. No differences between the two cultivars existed in the carbon exudation rate per gram dry root.Much higher concentrations of low molecular dicarboxylic acids i.e. succinic, malic and oxalic acid, were found in the exudates of aluminium-tolerant plants. Dicarboxylic acids are potential chelating compounds for positively charged metals such as aluminium and they may play an important role in protecting the plant against aluminium incorporation. They are also very suitable substrates for Azospirillum spp. It is therefore suggested that these factors may be causing the higher associative nitrogen fixation rates which was found in the aluminium-tolerant wheat cultivars.     

Pure culture growth of ectomycorrhizal fungi on inorganic nitrogen sources

Four ectomycorrhizal fungi were tested for their ability to grow (i.e., mycelial mat radial extension and fungal biomass) on nutrient media either supplemented with ammonium-nitrogen or nitrate-nitrogen or in the absence of an inorganic nitrogen source.Pisolithus tinctorius, Cenococcum geophilum andThelephora terrestris exhibited greater growth on ammonium-nitrogen.Suillus granulatus grew better on the nitrate-nitrogen nutrient medium. Regardless of inorganic nitrogen form preference (i.e., ammonium-nitrogen or nitrate-nitrogen), all 4 species showed some growth on each of the 3 nutrient media. Growth rate maxima varied by fungal species as well as by inorganic nitrogen source. Maximum growth rate forT. terrestris exceeded rates exhibited by the other 3 fungi by 2–5 times.     

Degradation and transformation of humic substances by saprotrophic fungi: processes and mechanisms

Humic substances represent the main carbon reservoir in the biosphere, estimated at 1600 × 10¹⁵ g C. Due to their crucial role in reductive and oxidative reactions, sorption, complexation and transport of pollutants, minerals and trace elements, sustaining plant growth, soil structure and formation, and control of the biogeochemistry of organic carbon in the global ecosystem, humic substances are extremely important to environmental processes. Saprotrophic fungi active in the decomposition process of humic substances include mainly ascomycetes and basidiomycetes, which are both common in the upper layers of soils. White rot and litter decomposing fungi are the most important organisms in the degradation and mineralization of refractory organic matter (OM), whereas ascomycetes are mainly involved in the modification and polymerization of humic substances. The mechanisms of degradation probably involve mainly a variety of non specific oxidizing enzymes. This review provides an overview of the subject, while bridging two main disciplines: soil OM chemistry and fungal microbiology. It is aimed to highlight problems, unsolved questions and hypotheses.     

Effects of acid irrigation and liming on the production of fruit bodies by ectomycorrhizal fungi

The aim of this work was to examine the effects of an increase in acid rain upon community diversity and productivity of the ectomycorrhizal fungi in a Norway spruce stand and the possible amelioratory effects of liming. No obvious adverse effects on either the diversity or productivity were found. Acid irrigation appeared to enhance the fruiting of Russula ochroleuca, as did irrigation with normal rain. A combination of acid irrigation and liming resulted in a large increase in the fruiting of Hygrophorus pustulatus. Thirty times more fruit bodies were recorded from this treatment than from the control. A principal component analysis of the fruit body data suggested that soil organic horizon pH may be an important determinant of ectomycorrhizal community structure within the spruce stand.