Effect of mycorrhiza and nitrate nutrition on nitrate reductase activity in Scots pine seedlings

In vivo nitrate reductase (EC 1.6.6.1) activity was measured in seedlings of Scots pine ( Pinus sylvestris L.) inoculated with Cenococcum geophilum (Sow.) Ferd. & Winge, Paxillus involutus (Batsch:Fr) Fr, Piloderma croceum Erikss, & Hjortst, and Suillus variegatus (Fr.) O. Kuntze. The activity was higher in the mycorrhizal pine roots than was previously found in the fungus symbiont alone, but lower than in the roots of nonmycorrhizal pine seedlings. The differences observed in a previous study between the fungal species under pure culture conditions were not found in the present work for mycorrhiza synthezised with the same fungal species. An increase in the nitrate concentration of the nutrient solution increased the proportion of the nitrate reductase activity in the needles. The mycorrhizal root tips had higher nitrate reductase activity than nonmycorrhizal root tips in the same root system.     

Distribution of lead in mycorrhizal and non-mycorrhizal Norway spruce seedlings

Non-mycorrhizal spruce seedlings (Picea abies Karst.) and spruce seedlings colonized with Lactarius rufus (Scop.) Fr. or two strains of Paxillits involutus (Batsch) Fr. were grown in an axenic silica sand culture system with frequently renewed nutrient solution. After successful mycorrhizal colonization, the seedlings were exposed to 1 μM PbCI₂ for 19 weeks. The degree of infection in all of the mycorrhizal treatments approached 100% during the experiment and was not affected by exposure to Pb. However, the number of root tips per root dry weight and the shoot: root ratio, both in the non-mycorrhizal and the mycorrhizal seedlings, had decreased after the 19 week treatment with PbCl₂ Using X-ray microanalysis, the distribution and concentration of Pb in the tissues of mycorrhizal and non-mycorrhizal root tips were compared. In the mycorrhizae of seedlings exposed to Pb no significant accumulation of Pb in the hyphal mantle or in fungal cell walls of the Hartig net were detected. Lead accumulated primarily in the cortex cell walls both of non-mycorrhizal and mycorrhizal root tips. No significant difference of Pb concentrations in root cortex cell walls of non-mycorrhizal and mycorrhizal seedlings was found; except for seedlings colonized with Paxillus involutus strain 537. However, at the endodermis no effect of mycorrhizal fungal colonization on the Pb tissue concentration was detected. The presence of the fungal sheath did not prevent Pb from reaching the root cortex. The endodermis acted as a barrier to Pb radial transport in both mycorrhizal and non-mycorrhizal seedling roots.     

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.     

Cytolocalization of glycogen, starch, and other insoluble polysaccharides during ontogeny of Paxillus involutus–Betula pendula ectomycorrhizas

The Paxillus involutus (Fries) Karsten– Betula pendula Roth association was studied during the early stages of formation. Cytological studies revealed fungal colonization behind the root cap and gradually around the entire root apex. Ultrastructural investigations were carried out and insoluble polysaccharide distribution was followed. The density of starch grains increased in plant cells especially after 4 d of contact between the two partners, but later on decreased strongly in the root cap. Large amounts of glycogen were revealed in the hyphae in certain mycorrhizal regions after 6 d of contact: in the Hartig net, in the inner sheath but only near the net, and all along the outer sheath surrounding the mycorrhiza. Thickenings of the epidermal cell walls were detected as early as 2 d after contact and then varied according to the distance from the root tip. Such polysaccharide distributions are assumed to show a transfer of carbohydrates from the root to the fungus and are discussed in terms of carbon requirements for both partners.     

Ectomycorrhizal weathering of the soil minerals muscovite and hornblende

Ectomycorrhizal fungi are hypothesized to enhance mineral weathering in forest soils. Several studies have shown an increased uptake of mineral-derived nutrients by trees when in symbiosis with ectomycorrhizal fungi. However, it is difficult to determine from these studies if the improved nutrient uptake is the result of increased weathering or better exploitation of the substrate by the ectomycorrhizal fungi. In a pot experiment, Pinus sylvestris (Scots pine) seedlings were grown with or without ectomycorrhizal fungi, and with or without the mineral muscovite as the only potassium (K) source or the mineral hornblende as the only magnesium (Mg) source. After 27 wk, all pools of non-mineral-bound K or Mg were determined. The ectomycorrhizal fungus Paxillus involutus increased weathering of muscovite but not hornblende. The other ectomycorrhizal fungi tested, Piloderma croceum and Suillus bovinus, did not increase weathering of either muscovite or hornblende compared with the nonmycorrhizal trees. The P. involutus-mediated mobilization of K from muscovite resulted in increased K content of root plus adhering hyphae, but not of shoots. In conclusion, ectomycorrhizal fungi may increase weathering of minerals in response to nutrient deficiencies, but this response is species specific.     

Effect of nitrate and ammonium concentration on nitrate reductase activity in five species of mycorrhizal fungi

The nitrate reducing capacity of pure cultures of Cenococcum geophilum (Sow.) Ferd. & Winge, Paxillus involutes (Batsch: Fr.) Fr. (strains 1 and 2), Piloderma croceum Erikss. & Hjortst., Suillus variegatus (Fr.) O. Kuntze (strains 1 and 2) and an ectendomycorrhizal (E-strain) fungus was measured using an in vivo nitrate reductase (EC 1.6.6.3) assay. Differences between species and strains were established. The nitrate concentration of the culture medium influenced the nitrate reductase activities of the E-strain fungus and one strain of S. variegatus. The nitrate reductase activity of certain species and strains was a function of nitrate concentration. Addition of ammonium to the growth medium did not have any significant effect on the in vivo or in vitro nitrate reductase activity. The in vivo nitrate reductase activity in the mycelia of C. geophilum and the E-strain fungus decreased during 28 day growth in modified Melin-Norkrans medium. For mycelia of Paxillus involutus, Piloderma croceum and S. variegatus grown on agar the in vitro assays showed higher nitrate reductase activity than the in vivo assays.     

Chitin and ergosterol combined to measure total and living fungal biomass in ectomycorrhizas

We have studied the chitin and ergosterol contents of ectomycorrhizal roots in three sets of experiments to evaluate them as indicators of fungal biomass. The first set of experiments showed that ageing had a marked effect on ergosterol concentrations. The ergosterol content of 7-month-old, brown, shrunken Pinus sylvestris L.– Paxillus involutus (Fr.) Fr. mycorrhizas was found to be only 10% of that found in white, turgid, 1- or 4-month-old specimens. This supports the hypothesis that the compound is a good indicator of living fungal biomass. Ageing had a lesser effect on chitin concentrations since the chitin levels found in 7-month-old mycorrhizas were still 60% of the levels found in 1- and 4-month-old specimens.
Consequently, the chitin:ergosterol ratio increased from about 14 to 19 in 1- and 4-month-old mycorrhizas respectively to about 110 in 7-month-old mycorrhizas. In the second set of experiments, we found that variation in plant growth had no effect on the chitin:ergosterol ratio in whole root systems of either Alnus incana (L.) Moench or Pinus sylvestris mycorrhizal with Paxillus involutus . In the third set of experiments, we found a constant relationship between the two marker concentrations in 10-month-old root systems of Pinus sylvestris , regardless of fungal species involved, using Paxillus involutus , Piloderma croceum Erikss. & Hjorts and Suillus variegatus (Fr.) O. Kuntze as test organisms. Taken together, the results of this study suggest that both chitin and ergosterol give reliable, but different, relative measures of fungal biomass in mycorrhizal roots. Furthermore, we demonstrate that, in combination, the two chemical markers can be used to estimate both total and living fungal biomass (derived from the chitin:ergosterol ratio).     

Apatite as a P source in mycorrhizal and non-mycorrhizal Pinus sylvestris seedlings

The objectives of the study are firstly to test the ability of ectomycorrhizal pine seedlings to use apatite as a P source in comparison with non-mycorrhizal pine seedlings and secondly, to determine if there is a relation between exudation of organic acids and the ability to use apatite as a P source. Non-mycorrhizal Pinus sylvestris (L.) seedlings and seedlings ectomycorrhizal with 4 different isolates of ectomycorrhizal fungi were grown for 220 days in sand/peat filled pots with apatite (Ca₅(F,OH)(PO₄)₃) as the sole P source. In an additional experiment, non-mycorrhizal Pinus sylvestris (L.) seedlings and seedlings ectomycorrhizal with 2 different isolates of ectomycorrhizal fungi were grown without any P source for 250 days. All other nutrients were supplied in a balanced nutrient solution.Ectomycorrhizal seedlings grew less than non-mycorrhizal seedlings but ectomycorrhizal seedlings produced a large external mycelium not included in the biomass estimates. All seedlings in the present study had low shoot:root ratios compared to seedlings growing under optimal conditions. All seedlings grown with apatite as P source had higher foliar P concentrations (0.71–2.11 mg/g) than seedlings growing without any P source (0.57–0.75 mg/g) indicating a significant ability to use apatite as a P source. Seedlings colonized by Suillus variegatus and Paxillus involutus had higher concentrations and total contents of P in shoots compared with non-mycorrhizal seedlings, indicating significant improvement of P uptake by these fungi in comparison with non-mycorrhizal seedlings or seedlings colonized Piloderma croceum.No clear relationship between exudation of organic acids and uptake of P was found. Seedlings colonized by S. variegatus reduced the pH of the soil more than seedlings colonized by P. involutus or non-mycorrhizal seedlings. It is suggested that S. variegatus colonization improves the P uptake by reducing the pH of the soil while P. involutus improves P uptake by having a greater ability to absorb dissolved phosphate than non-mycorrhizal roots or roots colonized by the other fungi used in the study.     

Solubilisation and colonisation of wood ash by ectomycorrhizal fungi isolated from a wood ash fertilised spruce forest

In Sweden application of granulated wood ash has been suggested as a method to supplement nutrient loss resulting from harvesting of forest residues for bioenergy production. Mycelia of two ectomycorrhizal fungi Piloderma sp. 1 and Ha-96-3, were commonly found to colonise ash granules in a wood ash fertilised spruce forest. Thirty-eight fungal isolates were selected from 10 taxa to investigate the possible role of different ectomycorrhizal fungi in nutrient mobilisation from ash. The taxa were Cenococcum geophilum Fr., Piloderma croceum Erikss. and Hjortst., Piloderma sp. 1, Thelephora terrestris (Ehrenb.) Fr., Tylospora fibrillosa Donk, and five unidentified species, all originating from a wood ash fertilised spruce forest. The isolates were tested for their ability to solubilise tricalcium phosphate (TCP) or hardened wood ash (HWA) in vitro. Ha-96-3, P. croceum and Piloderma sp. 1 were the only taxa which solubilised TCP. Abundant calcium oxalate crystals were formed in TCP and HWA plates with Piloderma sp. 1. Ha-96-3 and two isolates of P. croceum produced intermediate amounts of crystals. Ha-96-1 and T. fibrillosa produced low amounts of crystal but no crystal formation was observed by any of the other isolates. Piloderma sp. 1 from HWA plates had significantly higher concentrations of P, compared to P. croceum or Ha-96-3. Piloderma sp. 1 and P. croceum were further tested for their ability to colonise wood ash in microcosms containing intact mycorrhizal associations. After 7 months Piloderma sp. 1 colonised ash amended patches with a dense, mat like mycelium, whereas P. croceum mycelia avoided the ash patches. Possible differences between these fungi in patterns of carbon allocation were investigated by labelling seedlings with 14CO(2). Piloderma sp. 1 mycelia allocated significantly more 14C to ash patches than P. croceum. P. croceum allocated relatively more 14C to control patches than to the ash patches. The possible role of ectomycorrhizal fungi in mobilisation of nutrients from wood ash is discussed.     

Quantitative detection of agar-cultivated and rhizotron-grown<Emphasis Type="Italic"> Piloderma croceum</Emphasis> Erikss. &; Hjortst. by ITS1-based fluorescent PCR

A real-time quantitative TaqMan-PCR was established for the absolute quantification of extramatrical hyphal biomass of the ectomycorrhizal fungus Piloderma croceum in pure cultures as well as in rhizotron samples with non-sterile peat substrate. After cloning and sequencing of internal transcribed spacer (ITS) sequences ITS1/ITS2 and the 5.8S rRNA gene from several fungi, including Tomentellopsis submollis, Paxillus involutus, and Cortinarius obtusus, species-specific primers and a dual-labelled fluorogenic probe were designed for Piloderma croceum. The dynamic range of the TaqMan assay spans seven orders of magnitude, producing an online-detectable fluorescence signal during the cycling run that is directly related to the starting number of ITS copies present. To test the confidence of the PCR-based quantification results, the hyphal length of Piloderma croceum was counted under the microscope to determine the recovery from two defined but different amounts of agar-cultivated mycelia. Inspection of the registered Ct values (defined as that cycle number at which a statistically significant increase in the reporter fluorescence can first be detected) in a 10-fold dilution series of template DNA represents a suitable and stringent quality control standard for exclusion of false PCR-based quantification results. The fast real-time PCR approach enables high throughput of samples, making this method well suited for quantitative analysis of ectomycorrhizal fungi in communities of natural and artificial ecosystems, so long as applicable DNA extraction protocols exist for different types of soil.     

Cross-colonization of Scots pine (Pinus sylvestris) seedlings by the ectomycorrhizal fungus Paxillus involutus in the presence of inhibitory levels of Cd and Zn

The effects of Cd and Zn on cross-colonization by Paxillus involutus of Scots pine seedlings was examined by using pairs of ectomycorrhizal (ECM) and non-mycorrhizal (NM) seedlings grown in the same vessel. This was done to assess, first, the ability of P. involutus to colonize NM Scots pine seedlings by growth from colonized roots of other Scots pine seedlings in the presence of Cd or Zn, and, second whether ECM colonization of Scots pine by P. involutus provided a competitive advantage over NM seedlings. Ectomycorrhizal colonization of Scots pine was shown to be more sensitive than Scots pine itself to Cd and Zn, but prior colonization did provide a competitive advantage with respect to biomass production. This beneficial effect over NM seedlings was, however, equal in the control, Cd and Zn treatments, and was due simply to growth stimulation in the presence of ECM colonization. Cross-colonization from an ECM to a NM seedling was reduced but not prevented by Cd and Zn. Cd had a more negative effect on cross-colonization than on initial colonization of seedlings, whereas Zn had an equally inhibitory effect on both parameters. These results have important implications for plant establishment on metal-contaminated sites. If cross-colonization between plants is reduced by toxic metals, plant establishment on contaminated sites might be retarded.     

Colonisation of spruce roots by two interacting ectomycorrhizal fungi in wood ash amended substrates

Interactions between two ectomycorrhizal fungal species, Piloderma croceum Erikss. and Hjortst. and Piloderma sp. 1 (found to colonise spruce roots and wood ash granules in the field), were investigated in wood ash amended substrates. The comparative ability of these fungi to colonise roots of non-mycorrhizal spruce (Picea abies (L.) Karst.) seedlings was studied in relation to factorial combinations of wood ash and N fertilisation. Non-mycorrhizal spruce seedlings (bait seedlings) were planted together with spruce seedlings colonised by P. croceum or Piloderma sp. 1. The growth substrate was a sand-peat mixture with wood ash or no ash and supplied with two levels of N, so that four substrate combinations were obtained. Piloderma sp. 1 mycelia colonised around 60% of the fine roots of bait seedlings in ash treatments regardless of N level and around 20-26% in treatments without ash. P. croceum only colonised 8% of the root tips in the presence of ash but 56% of the root tips in the low-N treatment without ash. However, in the high-N treatment without ash the colonisation level was reduced to around 30%. Total numbers of root tips per seedling did not vary significantly between the treatments. Possible reasons for the competitive advantage of Piloderma sp. 1 in wood ash fertilised substrate are discussed.     

Mobilization and transfer of nutrients from litter to tree seedlings via the vegetative mycelium of ectomycorrhizal plants

The ability of the mycorrhizal fungus Paxillus involutus to mobilize nitrogen and phosphorus from discrete patches of beech ( Fagus sylvatica ), birch ( Betula pendula ) and pine ( Pinus sylvestris ) litter collected from the fermentation horizon of three forest soils, and to transfer the nutrients to colonized B. pendula Roth seedlings, was investigated in transparent observation chambers. The mycelium of P. involutus foraged intensively in all three types of litter, leading to a significant decline in their phosphorus contents after 90 d. Over the same period only one of the litter types, beech, showed more than a 10% loss of its N contents. Exploitation of the litter led to invigoration of the vegetative mycelium of the fungus throughout the chambers as well as to significant increases of biomass production and leaf area in seedlings grown in the plus litter (+L) relative to those in minus litter (−L) systems. The yield increases were associated with gains in whole plant tissue content and concentration of P, but in content only in the case of N. Calculations suggest that a major proportion of the phosphorus lost from litter originated in its organic fraction. The possible basis of the discrepancy between values of N loss from litter and gain by the plant is discussed and the extent to which the distinctive pattern of nutrient mobilization is a feature peculiar to this fungus-plant combination is considered. It is concluded that nutrient mobilization from natural organic substrates in the fermentation horizon of forest soils may be a key function of the vegetative mycelium of mycorrhizal systems. The need for experimental analyses of a greater range of fungus-plant partnerships is stressed.     

Production of fungal and bacterial growth modulating secondary metabolites is widespread among mycorrhiza-associated streptomycetes

ABSTRACT: BACKGROUND: Studies on mycorrhiza associated bacteria suggest that bacterial-fungal interactions play important roles during mycorrhiza formation and affect plant health. We surveyed Streptomyces Actinobacteria, known as antibiotic producers and antagonists of fungi, from Norway spruce mycorrhizas with predominantly Piloderma species as the fungal partner. RESULTS: None of the fifteen Streptomyces isolates inhibited all seven tested mycorrhizal and plant pathogenic fungi (Amanita muscaria, Fusarium oxysporum, Hebeloma cylindrosporum, Heterobasidion abietinum, Heterobasidion annosum, Laccaria bicolor, Piloderma croceum). The growth of only one of the tested fungi, the mycorrhiza-forming fungus Laccaria bicolor, was stimulated by the streptomycetes, and Piloderma croceum was only moderately affected. Bacteria responded to the streptomycetes differently than the fungi. For instance the strain Streptomyces sp. AcM11, which inhibited most tested fungi, was less inhibitory to bacteria than other tested streptomycetes. The determined patterns of Streptomyces-microbe interactions were associated with distinct patterns of secondary metabolite production. Notably, potentially novel metabolites were produced by strains that were less antagonistic to fungi. Most of the identified metabolites were antibiotics (e.g. cycloheximide, actiphenol) and siderophores (e.g. ferulic acid, desferroxiamines). Plant disease resistance was activated by a single streptomycete strain only. CONCLUSIONS: Our results show that the primary characteristic of mycorrhiza associated streptomycetes is to inhibit the growth of fungi and bacteria. In parallel, our study indicates that Streptomyces strains which are not general antagonists may produce previously un-described metabolites.     

The role of ectomycorrhizal inoculations in landfill site restoration programmes

Greenhouse landfill models were used to examine the efficacy of the mycorrhizal fungus Paxillus involutus to promote the growth of Betula pendula (Silver Birch) seedlings in different site restoration strategies. Direct planting into refuse resulted in death of the fungal symbiont whilst with topsoil and subsoil no positive growth promotions, compared with uninoculated controls, resulted. With sterile seedlings, mycorrhizal associations formed within 24 weeks in both subsoil and topsoil. The need for mycorrhizal tree seedlings in site restoration programmes is, therefore, questioned.     

菌丝桥在日本落叶松幼苗间磷传递和植株生长中的作用

 应用四室隔网系统研究了菌丝桥在日本落叶松(Larix kaempferi)幼苗间传递磷的作用。结果表明,供体接种卷缘桩菇(Paxillus involutus)和彩色豆马勃（Pisolithus tinctorius）后,其外延菌丝可以穿过隔离层侵染受体落叶松,在供体和受体落叶松间形成了菌丝桥。供体植株接种菌根真菌后生物量明显增加,但是对受体植株没有显著的影响。菌根真菌侵染的供体和受体植株的根、地上部吸磷量均分别显著高于对照,而且供体植株根、地上部吸磷量增加的程度明显高于受体。被卷缘桩菇和彩色豆马勃侵染的受体植株体内32P的放射性强度分别是对照的10倍和6倍,两者形成菌丝桥后传递到受体植株的32P分别为供体植株体内32P的1.10%和0.22%。供体植株吸收的32P可以通过菌丝桥传递给受体,但是绝对数量十分有限,对受体植株磷营养没有产生显著的影响,但P. involutus和P. tinctorius侵染受体植株后,促进了受体落叶松对磷的吸收,这是菌丝桥形成后,真菌帮助受体植株吸收磷引起的。     

Media formulation influences in vitro ectomycorrhizal synthesis on the European aspen Populus tremula L.

The effect of various media formulations on in vitro ectomycorrhizal synthesis of identified fungal strains with European aspen (Populus tremula L.) was tested in Petri dishes. Pre-grown seedlings were transferred to various nutrient media and inoculated with Paxillus involutus isolates using modified sandwich techniques. Mycorrhiza formation was evaluated macroscopically and further confirmed by microscopic examination of semi-thin sections for anatomical features of the mantle and the Hartig net. Standard media formulations did not support successful ectomycorrhiza formation because of either very poor plant survival (below 20%) or impaired fungal growth. The inclusion of micronutrients and vitamins in a Melin Norkrans (MMN)-based medium increased plant survival rate to above 60% and supported successful mycorrhizal synthesis. P. involutus isolates formed mycorrhizas with a characteristic Hartig net restricted to the epidermis. Mantle density and thickness varied depending on the isolate. In a follow-up experiment, the adapted medium supported successful ectomycorrhiza formation by various Laccaria and Hebeloma isolates. Our results show that an exogenous supply of vitamins and micronutrients in the medium was a prerequisite for successful mycorrhization of P. tremula in vitro in Petri dishes.     

Microcosm-based analyses of Scots pine seedling growth, ectomycorrhizal fungal community structure and bacterial carbon utilization profiles in boreal forest humus and underlying illuvial mineral horizons

We report on the identity of indigenous mycorrhiza forming fungi and rhizosphere/mycorrhizosphere bacterial community carbon source utilization profiles of Scots pine (Pinus sylvestris L.) seedlings grown in boreal forest humus (O) or illuvial (B) mineral horizon containing microcosm growth systems. Based on rDNA (ITS)-RFLP analyses, a total of 10 fungal RFLP taxa were identified from pre-morphotyped mycorrhizas on 7-month-old seedling roots. Hierarchical cluster analysis, including corresponding RFLPs of known fungal species, confirmed root colonization by eight mycorrhizal species. In the O horizon, roots were colonized by e.g. Suillus bovinus, Suillus variegatus, Cenococcum geophilum, Piloderma croceum, Thelephora terrestris and Russula vinicolor. Mycobiont diversity in the mineral B horizon was lower but included Piceirhiza bicolorata and both Suillus species which produced extensive extramatrical mycelium. In comparison to non-colonized soils, rhizosphere and mycorrhizosphere compartments supported significantly higher numbers of bacteria (mean range 10(8)-10(11) cells g(-1) fresh weight (fw)). Specific rhizosphere/mycorrhizosphere 'niche'-linked bacterial communities were detected following multivariate analyses (PCA and CA) of bacterial carbon utilization profiles (Biolog(R) GN microplate). Distinct preferences for amino and carboxylic acids were identified in mineral B horizon rhizospheres whereas a wider range of carbon sources were utilized in the fungal-dominated mycorrhizospheres irrespective of soil types.     

The arbuscular mycorrhizal fungus Diversispora spurca ameliorates effects of waterlogging on growth,root system architecture and antioxidant enzyme activities of citrus seedlings

Citrus plants are often exposed to heavy rain and subsequent periods of soil waterlogging which severely restrict tree growth. We assessed the effect of one arbuscular mycorrhizal fungus species (Diversispora spurca) on growth, root system architecture (RSA), and antioxidant enzyme activities of young citrus (Citrus junos) seedlings. Waterlogging for 37 d significantly restricted mycorrhizal colonization but increased the number of entry points and vesicles. Compared with non-mycorrhizal controls, mycorrhizal seedlings had significantly greater plant height, fresh mass, total root and taproot lengths, projected and surface root areas, root volume, and numbers of lst, 2nd and 3rd order lateral roots regardless of waterlogging treatment. D. spurca significantly increased root catalase (CAT) activity in non-stressed seedlings and increased root soluble protein concentration and leaf CAT activity in waterlogged seedlings, thereby inducing lower oxidative damage. These results suggest that D. spurca ameliorates effects of waterlogging on growth, RSA and antioxidant enzyme activities.