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The effectiveness of two microbiologically treated agrowastes [dry olive cake (DOC) and/or sugar beet (SB)] on plant growth, soil enzymatic activities and other soil characteristics was determined in a natural soil from a desertified area. Dorycnium pentaphyllum, a legume plant adapted to stress situations, was the test plant to evaluate the effect of inoculation of native arbuscular mycorrhizal (AM) fungi and/or Yarowia lipolytica (a dry soil adapted yeast) on amended and non-amended soils. Plant growth and nutrition, symbiotic developments and soil enzymatic activities were limited in non-amended soil where microbial inoculations did not improve plant development. The lack of nodules formation and AM colonization can explain the limited plant growth in this natural soil. The effectiveness and performance of inocula applied was only evident in amended soils. AM colonization and spores number in natural soil were increased by amendments and the inoculation with Y. lipolytica promoted this value. The effect of the inoculations on plant N-acquisition was only important in AM-inoculated plants growing in SB medium. Enzymatic activities as urease and protease activities were particularly increased in DOC amended soil meanwhile dehydrogenase activity was greatest in treatments inoculated with Y. lipolytica in SB added soil. The biological activities in rhizosphere of agrowaste amended soil, used as indices of changes in soil properties and fertility, were affected not only by the nature of amendments but also by the inoculant applied. All these results show that the lignocellulosic agrowastes treated with a selected microorganism and its further interaction with beneficial microbial groups (native AM fungi and/or Y. lipolytica) is a useful tool to modify soil physico-chemical, biological and fertility properties that enhance the plant performance probably by making nutrients more available to plants. [Copyright &y& Elsevier]

During arbuscular mycorrhiza (AM) development, fungal hyphae grow throughout root epidermal, exodermal and cortical cell layers to reach the inner cortex where the symbiosis’ functional units, the arbuscles, develop. Three essential components of a plant signalling network, a receptor-like kinase, a predicted ion-channel and a calmodulin-dependent protein kinase have been identified. A detailed morphological study of symbiotic plant mutants revealed that different subsets of plant genes support the progress of fungal infection in successive root cell layers. Moreover, evidence of a diffusible fungal signalling factor that triggers gene activation in the root has recently been obtained. [Copyright &y& Elsevier]

Abstract: A field behaviour trial was set up in Mahela (Madagascar) to evaluate the ecological competence of two ectomycorrhizal fungal strains on Acacia crassicarpa. This fast-growing Australasian species is very well appreciated locally by farmers as multipurpose wood. However, its symbiotic associations with nitrogen fixing bacteria, ectomycorrhizas, and arbuscular mycorrhizas have been poorly studied so far. The inoculated fungal strains used in the present experiment belonged to two different species of the genus Pisolithus, strain 441 originating from Pisolithus microcarpus collected in Brazil under Eucalyptus citriodora and strain COI.007 from Pisolithus albus collected in Senegal under Acacia mangium. A survey of sporocarps fruiting in the inoculation trial and the molecular identification of the fungal partners present within the ectomycorrhizal roots showed the exclusive occurrence of the inoculant strain 441 in all the experimental plots of A. crassicarpa after 19 months of tree growth. The inoculant strain COI.007 was not detected in any plot. We confirmed the ability of A. crassicarpa to form ectomycorrhizal associations but exclusively with P. microcarpus in the field conditions tested here. The lack of growth response to inoculation that we observed could be attributed to the contamination of all plots by strain 441. [Copyright &y& Elsevier]

Addition of organic materials of various origins to soil has been one of the most common rehabilitation practices to improve soil physical properties. Mycorrhiza has been known to play a significant role in forming stable soil aggregates. In this study, a 5-year field experiment was conducted to explore the role of mycorrhizal inoculation and organic fertilizers on the alteration of physical properties of a semi-arid Mediterranean soil (Entic Chromoxerert, Arik clay-loam soil). From 1995 to 1999, wheat (Triticum aestivum L.), pepper (Capsicum annuum L.), maize (Zea mays L.) and wheat were sequentially planted with one of five fertilizers: (1) control, (2) inorganic (160–26–83 kg N–P–K ha-1), (3) compost at 25 t ha-1, (4) farm manure at 25 t ha-1 and (5) mycorrhiza-inoculated compost at 10 t ha-1. Soil physical properties were significantly affected by organic fertilizers. For soil depths of 0–15 and 15–30 cm, mean weight diameter (MWD) was highest under the manure treatment while total porosity and saturated hydraulic conductivity were highest under the compost treatment. For a soil depth of 0–15 cm, the compost and manure-treated plots significantly decreased soil bulk density and increased soil organic matter concentration compared with other treatments. Compost and manure treatments increased available water content (AWC) of soils by 86 and 56%, respectively. The effect of inorganic fertilizer treatment on most soil physical properties was insignificant (P>0.05) compared with the control. Mycorrhizal inoculation+compost was more effective in improving soil physical properties than the inorganic treatment. Organic fertilizer sources were shown to have major positive effects on soil physical properties. [Copyright &y& Elsevier]

Glomalin concentrations of extra-radical arbuscular mycorrhizal (AM) hyphae were estimated by deploying hyphal in-growth cores containing glomalin-free sand in field soils in a tropical forest and in pot cultures. In field soils, glomalin was 0.044±0.013 μg m-1 hyphae. In pot cultures glomalin concentrations were lower (range 0.0068–0.036 μg m-1), and varied significantly among species. Using this technique, preliminary estimates of extraradical AM hyphal production on Inceptisols were 1.91 Mg ha-1yr-1 and on Oxisol were 1.47 Mg ha-1 yr-1, but they could range between 0.9–5.7 Mg ha-1 yr-1. These rates of hyphal production are approximately 10% (range 5–33%) of estimated above ground primary production of the forest. [Copyright &y& Elsevier]

The influence of the arbuscular mycorrhizal fungus (AMF) Glomus macrocarpum Tul. and Tul. on Bradyrhizobium-inoculated soybean (Glycine max L. Merrill var. IAC-14) growth, nutrients and Pb uptake was studied in soils with different levels of Pb. Mycorrhizal and non-mycorrhizal plants were grown in a soil amended with 0, 150, 300 and 600 mg dm−3 of Pb, using Pb(NO3)2, and plants were harvested at two different growth stages: flowering and maturity. Soybean shoot dry weights were not affected by increasing doses of lead in the soil, but the number of pods decreased significantly. Nodule dry weights of mycorrhizal roots were reduced by soil Pb additions, although the mycorrhizae stimulated plant nodulation significantly. The inoculation of AMF in soybeans provided higher rates of nutrients uptake, mainly P, inducing greater mycorrhizal-soybean growth. Thus, mycorrhizae improved Pb uptake, produced shoots with Pb concentrations 30% lower than those of non-mycorrhizal plants, at the highest Pb concentration added to the soil. AM fungus was more susceptible to the higher Pb doses added to the soil than the soybean plants, decreasing both root AM colonisation and spore production. This work indicated that a concentration of 600 mg dm−3 of Pb in the soil interfered with the establishment of double symbioses between AMF and Bradyrizhobium, and with the fungus perpetuation in the soil. [Copyright &y& Elsevier]

Brazilian pine (Araucaria angustifolia, Araucariaceae) is one of the few native gymnosperms from southern Brazil. In Rio Grande do Sul, it occurs mainly in the highlands of the planalto region, as a tree-component of the mixed ombrophyllous forests. The species is valuable for its wood, edible seeds, and ornamental use, and is today listed as a threatened species. This tree-species establishes associations with arbuscular mycorrhizal fungi, and assessing the impact of such association to the species-performance will help us in defining the management procedures for its use in conservation and sustainable purposes. In this study, we tested the nutritional and growth responses of seedlings to inoculation with Glomus clarum, a fungal species identified in the rhizosphere of Brazilian pine in natural stands. A greenhouse study was conducted, where plants were either inoculated with G. clarum or with a sterilized version of the same inoculum. Plant growth was evaluated over a 21-month period by measuring the total shoot length, and, at the end, by plant dry mass, leaf nutrient content, and root colonization. Seedlings inoculated with G. clarum had a high degree of mycorrhizal colonization of their roots (81%). The inoculated seedlings grew significantly more (312% mass increase) than the controls, which had a higher root:shoot ratio than the inoculated seedlings. Leaf concentrations of P, K, Na, and Cu were higher while those of Ca, Mg, Fe, Mn, and B were lower in the inoculated plants. The results indicate a strong response of A. angustifolia to mycorrhizas, suggesting a high degree of dependence of the species on these associations. [Copyright &y& Elsevier]

A field experiment was undertaken to evaluate the effectiveness of mycorrhizal inoculation with Glomus intraradices (Schenck & Smith) or Glomus deserticola (Trappe, Bloss. & Menge) and the addition of sugar beet (SB), rock phosphate and Aspergillus niger with respect to the establishment of Dorycnium pentaphyllum L. seedlings, in a semiarid Mediterranean area, and the improvement of the physical-chemical, biochemical and biological properties of the soil. Eighteen months after planting, amended soil had higher available phosphorus and aggregate stability levels than control soil (165 and 157%, respectively). All assayed treatments had higher soil total carbohydrates and water soluble C values and enzyme activities (dehydrogenase, urease, acid phosphatase and β-glucosidase), and lower soil pH and bulk density than control soil. Biomass C and dehydrogenase, urease and β-glucosidase activities of the rhizosphere of G. deserticola-inoculated plants were higher than those of the rhizosphere of G. intraradices-inoculated plants. Mycorrhizal inoculation treatments stimulated significantly the production of shoot biomass, to a higher extent than the addition of the amendment alone to soil or the combined treatment. The highest levels of mycorrhizal colonisation and of foliar N and K were recorded in the seedlings inoculated with G. deserticola. The shoot biomass of G. deserticola-inoculated D. pentaphyllum plants was greater (about 219% with respect to control plants) than that of G. intraradices (about 116% with respect to control plants). [Copyright &y& Elsevier]

In vitro propagated plants are delicate and lacking vigor to survive the acclimatization shock with great losses observed frequently. Comparison of potting substrates showed that survival of Podophyllum peltatum plantlets was higher (97%) in a non-sterile soil (NS)–sand (2:1 v/v) substrate than in Miracle–Gro potting mix®-sand (2:1 v/v) with or without inocula of arbuscular mycorrhiza (AM). The non-sterile soil substrate was collected from areas of P. peltatum wild-grown colonies located on the University of Mississippi Campus. Within the group of plantlets grown in the Miracle–Gro potting mix®-sand substrate, the survival rate was significantly higher in plantlets inoculated with AM fungi. Plantlets inoculated with Entrophospora colombiana had a superior survival rate (73%) than plantlets inoculated with Glomus mosseae, Gigaspora ramisporophora or Scutellospora fulgida (57%). Ex vitro G. ramisporophora inoculated plants yielded more podophyllotoxin and related lignans than the control, non-inoculated plants. [Copyright &y& Elsevier]

Arbuscular mycorrhizal (AM) development in different soil types, and the influence of AM fungal hyphae on their original soil were investigated. Plantago lanceolata, which can grow in soils of a very wide pH range, was grown in two closely related limestone soils and an acid soil from rock habitats. Plants were colonised by the indigenous AM fungal community. The use of compartmented systems allowed us to compare soil with and without mycorrhizal hyphae. Root colonisation of P. lanceolata was markedly higher in the limestone soils (30–60%) than in the acid soil (5–20%), both in the original habitat and in the experimental study. Growth of extraradical AM fungal hyphae was detected in the limestone soils, but not in the acid soil, using the signature fatty acid 16:1ω5 as biomass indicator. Analysis of signature fatty acids demonstrated an increased microbial biomass in the presence of AM fungal hyphae as judged for example from an increased amount of NLFA 16:0 with 30 nmol g−1 in one of the limestone soils. Bacterial activity, but not soil phosphatase activity, was increased by around 25% in the presence of mycorrhizal hyphae in the first harvest of limestone soils. AM fungal hyphae can thus stimulate microorganisms. However, no effect of AM hyphae was observed on the soil pH or organic matter content in the limestone soils and the available P was not depleted. [Copyright &y& Elsevier]

Mycorrhizal associations, including ericoid, arbuscular and ecto-mycorrhizas, are found colonising highly metal contaminated soils. How do mycorrhizal fungi achieve metal resistance, and does this metal resistance confer enhanced metal resistance to plant symbionts? These are the questions explored in this review by considering the mechanistic basis of mycorrhizal adaptation to metal cations. Recent molecular and physiological studies are discussed. The review reappraises what constitutes metal resistance in the context of mycorrhizal associations and sets out the constitutive and adaptive mechanisms available for mycorrhizas to adapt to contaminated sites. The only direct evidence of mycorrhizal adaptation to metal cation pollutants is the exudation of organic acids to alter pollutant availability in the rhizosphere. This is not to say that other mechanism of adaptation do not exist, but conclusive evidence of adaptive mechanisms of tolerance are lacking. For constitutive mechanisms of resistance, there is much more evidence, and mycorrhizas possess the same constitutive mechanisms for dealing with metal contaminants as other organisms. Rhizosphere chemistry is critical to understanding the interactions of mycorrhizas with polluted soils. Soil pH, mineral weathering, pollutant precipitation with plant excreted organic acids all may have a key role in constitutive and adaptive tolerance of mycorrhizal associations present on contaminated sites. The responses of mycorrhizal fungi to toxic metal cations are diverse. This, linked to the fact that mycorrhizal diversity is normally high, even on highly contaminated sites, suggests that this diversity may have a significant role in colonisation of contaminated sites by mycorrhizas. That is, the environment selects for the fungal community that can best cope with the environment, so having diverse physiological attributes will enable colonisation of a wide range of metal contaminated micro-habitats. [ABSTRACT FROM AUTHOR]

In recent years, the major focus in nodulation research has been on the genetic dissection of Nod-factor signaling. Components of this pathway appear to be shared with signaling processes that are induced during the formation of mycorrhiza. With the cloning of orthologs of the NIN and DMI2 genes from several legumes, the molecular characteristics of components of the Nod-factor-signaling pathway are now starting to be revealed. Orthologs of HAR1, a key player in the systemic autoregulatory mechanism controlling nodule numbers, have also been cloned recently. The mechanism by which nodulation is autoregulated is related to that by which fixed nitrogen inhibits nodulation. Genes that are involved in Nod-factor signaling may be targets for mechanisms that suppress nodulation. If this is the case, it would bring two fascinating areas of symbiosis together. [Copyright &y& Elsevier]

Recent studies suggest that ultraviolet-B radiation, a major component of global climate change, can affect the community structure, biomass and functioning of terrestrial microorganisms. In this report, these studies are reviewed and gaps in our understanding highlighted so that future research can provide more conclusive evidence on the mechanisms and wider ecological implications of the impacts of elevated ultraviolet-B radiation on terrestrial microorganisms. [Copyright &y& Elsevier]

The interaction between the salt marsh plant Spartina patens, arbuscular mycorrhizal fungi (AMF) and bacteria in salt marsh sediment was examined in a long-term arbuscular mycorrhizas (AM) suppression study by applying the systemic fungicide benomyl to field-collected sediment cores with and without S. patens plants. Microbial populations were sampled four times corresponding to major plant phenological stages (dormancy, vegetative growth, reproduction, and senescence) previously linked to changes in microbial populations under field conditions. Benomyl-treatment of soil cores significantly suppressed AM colonization on S. patens, keeping values relatively consistent throughout the growing season (11.5%) whereas plants in non-treated cores experienced seasonal increases and declines in AM colonization (26.6% during vegetative growth to 11.5% during dormancy). Soil physicochemical parameters were not affected by benomyl application. In unvegetated cores, no benomyl- or seasonal effects were displayed by cell numbers and specific biomass of DAPI-stained organisms, members of the domain bacteria and here especially members of the α-, β-, γ- and δ-subdivisions of proteobacteria that were the most abundant bacterial groups. In vegetated cores, the microbial community as well as specific bacterial populations were at least twice as large in terms of number and biomass than in samples from unvegetated cores with significant seasonal changes for DAPI-stained cells, for members of the domain bacteria and for members of the α- and γ-subdivisions of proteobacteria. In benomyl-treated cores, the population of γ-subdivision of proteobacteria was significantly smaller than in non-treated cores, and a positive association was found between this bacterial group and root length colonized by AM suggesting that AM-suppression can affect populations of specific soil bacterial populations in salt marsh sediment. Benomyl-treatment had no effect on the diversity of N-fixing bacteria as evidenced by PCR-RFLP analysis, but seasonal changes were noted in vegetated cores with populations during active plant growth substantially different from populations during dormancy and senescence. [Copyright &y& Elsevier]

Electroshocking has been used to manipulate earthworm populations in agroecosystems. However, data on the effects of electroshocking on vegetation are lacking. Here we report on a field experiment with the aim to validate electroshocking as a means of manipulating earthworms without otherwise affecting the soil–plant system. We showed that there was no effect of electroshocking on canopy CO2 exchange, root respiration or mycorrhizal fungal abundance and vitality (i.e. the proportion of mycorrhizal fungal structure which was alive). The potential for using electroshocking to manipulate earthworm populations in the field and test ecological hypotheses relating to the role of soil biodiversity in soil processes is discussed. [Copyright &y& Elsevier]

Root distribution and mycorrhizal associations were compared in primary, secondary and limestone forests in Xishuangbanna, southwest China. Soil cores to a depth of 20 cm were collected at random points from four 50 m2 quadrats in each forest type. Arbuscular mycorrhizal (AM) associations were the only form of mycorrhiza found in all forest types. The primary forest was characterized by high root mass, root lengths and AM colonization levels higher than other forest types. In contrast, secondary forests had greater AM fungal spore numbers and specific root length, indicating that plant species in secondary forests achieved a greater degree of soil exploration with less biomass allocation to roots. Root density, AM colonization and AM fungal spore numbers decreased with soil depth in all forest types. Although the correlation between AM colonization levels and spore numbers was insignificant when all forest types were considered together, significant relationships emerged when each forest type was considered individually. AM colonization and spore numbers were correlated with several root variables. [Copyright &y& Elsevier]

Two greenhouse experiments were conducted on the biological and nutritional effects of vermicompost on Sorghum bicolor growth and root infection by arbuscular mycorrhizal fungi (AMF). Two rates of sterile and non-sterile vermicompost (5% and 20%) were added to two media (peat and mineral). In experiment 1, all treatments received AMF inoculant but in experiment 2 uninoculated treatments were included. The addition of vermicompost to substrates increased N, P and K levels. Vermicompost stimulated mycorrhizal colonization of roots in both experiments, particularly in the peat medium. Shoot and root dry weights were increased by vermicompost in the absence of AMF. Inoculation with AMF reduced dry weights particularly at the higher rate (20%) of vermicompost. Steam sterilization of vermicompost had no consistent effect on mycorrhizal colonization but generally enhanced dry weights relative to the non-sterile treatment. [ABSTRACT FROM AUTHOR]

An evaluation of the mycorrhizal status of desertification-threatened ecosystems has been recommended as a first step in rehabilitation/restoration approaches based on revegetation strategies using arbuscular mycorrhizal (AM) technology. Representative desertified semiarid areas were selected from southeast Spain where the vegetation is dominated by grasses, with Stipa tenacissima usually present, and with some patches of the shrubs Pistacia lentiscus, Rhamnus lycioides, Olea europaea subsp. sylvestris and Retama sphaerocarpa. The objective of this study was to evaluate the mycorrhizal potential in these soils, the contribution of the different species established to the mycorrhizal potential of the soils and to assess the main mycorrhizal propagules involved. There were more AM fungal propagules in the rhizospheres of all the shrub species studied compared with adjacent fallow soils, suggesting that AM propagules can be considered as a functional component of the resource islands developing around plant roots. R. sphaerocarpa and O. europaea had a higher capacity to enhance the development of mycorrhizal propagules in their rhizospheres than R. lycioides and P. lentiscus. Correlation analyses showed that the number of spores of the most representative AM fungal species, i.e. Glomus constrictum, and the total length of extraradical AM mycelium are the propagule sources which were best correlated with the mycorrhizal potential in terms of the number of “infective” AM propagules in the rhizosphere of the target plant species. The contribution of AM symbiosis to the potentiality of S. tenacissima as nurse plant was site dependent. Diversity of AM fungi present in the test area is rather low, indicating the high degree of degradation of the ecosystem. At most, only four AM fungal spore morphoecotypes were consistently detected in the rhizosphere of the target plant species. [Copyright &y& Elsevier]

The biocontrol bacterium Burkholderia cepacia is known to suppress a broad range of root pathogenic fungi, while its impact on other beneficial non-target organisms such as arbuscular mycorrhizal (AM) fungi is unknown. Direct interactions between five B. cepacia strains and the AM fungus, Glomus intraradices (BEG87) were studied in root-free soil compartments separated from a rooting compartment by a fine nylon-mesh. B. cepacia had no effect on AM fungal biomass and energy reserves measured using the signature fatty acid 16:1ω5 from phospholipid fatty acids (PLFAs) and neutral lipid fatty acids (NLFAs), respectively. Hyphal P transport was also unaffected by the biocontrol bacterium, which either stimulated, reduced or had no effect on length of the external mycelium of G. intraradices. The cyclic PLFAs cy17:0 and cy19:0 were suggested to be useful markers for estimation of biomass of B. cepacia. The presence of mycelium of G. intraradices reduced the biomass of three out of five B. cepacia strains as indicated by a reduction in PLFAs cy17:0 and cy19:0, while other bacterial PLFAs were unaffected by mycelium of G. intraradices. On the other hand, two out of five B. cepacia strains reduced the amount of branched PLFAs suggesting a reduction in the population of Gram-positive bacteria in these cases. In conclusion, the B. cepacia seems to have no impact on neither mycorrhiza formation nor on the functioning of the AM fungus G. intraradices in terms of P transport, whereas our results suggest that mycorrhiza might have adverse effects on B. cepacia. [Copyright &y& Elsevier]

We studied the influence of olive mill dry residue (DOR) on growth of soybean (Glycine max) and lettuce (Lactuca sativa) colonized with the arbuscular fungi Glomus mosseae or G. deserticola. The DOR has 6 mg g−1 of soluble phenolic compounds and the application of 2.5 g kg−1 of DOR (15 mg kg−1 of phenolic content) to soil decreased the growth of plants colonized with the AM fungi. The application to the soil of 10 g kg−1 of DOR (60 mg kg−1 of phenolic content) decreased the dry weight of nonarbuscular mycorrhizal (AM) plants. The application of DOR decreased the percentage of AM colonization of plants except those were inoculated with G. mosseae or G. deserticola 4 weeks before the application of DOR. No effect of the residue on the colonization of these previously AM inoculated plants was observed. DOR had no effect neither on the fungal succinate dehydrogenase activity nor on the most probable number of AM propagules in all treated soils. The obtained results showed than AM fungi increased the phytotoxicity of DOR in lettuce and soybean. [Copyright &y& Elsevier]

Plant roots form intracellular symbioses with fungi and bacteria resulting in arbuscular mycorrhiza and nitrogen-fixing root nodules, respectively. A novel receptor like-kinase has been discovered that is required for the transduction of both bacterial and fungal symbiotic signals. This kinase defines an ancient signalling pathway that probably evolved in the context of arbuscular mycorrhiza and has been recruited subsequently for endosymbiosis with bacteria. An ancestral symbiotic interaction of roots with intracellular bacteria might have emerged from such a recruitment, in the progenitor of the nodulating clade of plants. Analysis of symbiotic mutants of host plants and bacterial microsymbionts has revealed that present-day endosymbioses require the coordinated induction of more than one signalling pathway for development. [ABSTRACT FROM AUTHOR]

The movement of carbon from plants into their natural communities of arbuscular-mycorrhizal (AM) fungi was investigated. Mesh-bound cores, which allowed in-growth of AM mycelium to be controlled but excluded roots, were inserted into turf monoliths removed from an upland grassland and were exposed to 14CO2. Flux of 14C-labelled carbon from plants to hyphae of AM fungi for 70 h post-labelling was measured by (a) trapping CO2 released from soil cores containing AM hyphae linked to the plants compared to cores from which AM hyphal connections to the plant roots had been severed, and (b) quantification of the total amount of 14C in the cores. Release of 14CO2 from the cores colonised by active AM mycelium was highest for 0–28 h from the onset of labelling and declined rapidly thereafter. The amount of 14C allocated into mycorrhizal mycelium 0–70 h after labelling accounted for 3.4% of the 14C initially fixed by the plants. The results confirm the rapidity of photosynthate allocation to AM mycelium and demonstrate the importance of the short-term dynamics of C fluxes in undisturbed grasslands. [Copyright &y& Elsevier]

Alpha grass (Stipa tenacissima) steppes are widely distributed within the semi-arid areas of the Mediterranean Basin, and represent a degraded stage of vegetation. We evaluated the effect of S. tenacissima tussocks and nursery inoculation with mycorrhizae on the survival of the native shrub Quercus coccifera. Experiments were carried out in three steppes located in semi-arid southeastern Spain. Survival during the first months after plantation was significantly higher in the surroundings of S. tenacissima tussocks than in open areas between the tussocks. We did not find any effect of nursery inoculation on seedling survival. This effect may be related to the fact that the used fungal strain did not survive the drought summer conditions in the study area. Our results support the idea of a facilitative effect of S. tenacissima on introduced shrubs, which may be related to improved environmental conditions in tussock microsites. However, this effect may not be enough for the establishment of seedlings in years with below-average rainfall and a strong summer drought. [Copyright &y& Elsevier]

A research study has been performed in a natural soil of Senegal to follow the development of four provenances of Acacia mangium inoculated with an ectomycorrhizal fungus Pisolithus sp. (strain COI024) and/or a Bradyrhizobium sp. isolate (Aus 13c), to evaluate the impact of these symbioses on the microbial biomass and on the indigenous rhizobial and fungal symbiotic microflora and to determine the impact of these controlled inoculations on the structure of nematode communities.The results showed that the dual inoculation significantly improved plant growth for all provenances. When the plants were transferred into 20 l pots filled with a non-sterilized soil, the positive effect on the plant growth of the dual inoculation disappeared and no significant difference was recorded between the plants inoculated with the fungus alone and those inoculated with both Bradyrhizobium and the ectomycorrhizal fungus. However, the microbial biomass, the nitrogen contents, the number of nodules per plant and the structure of the nematode communities were significantly influenced by the A. mangium provenances and the microbial treatments. The impact of controlled mycorrhization of different A. mangium provenances on soil biofunctioning is discussed in terms of plant growth, microbial and nematode biodiversity. [Copyright &y& Elsevier]

A field experiment was undertaken to evaluate the effect of mycorrhizal inoculation with Glomus intraradices and added composted residue on the establishment of Pistacia lentiscus L. seedlings in a semiarid area. Composted residue greatly increased macronutrient (NPK) content, soil microbial activity and enzymatic activities, and decreased soil bulk density. There was a significant correlation between soil bulk density and both enzyme activities and labile C fractions (water-soluble C and water-soluble carbohydrates), which are also related to soil microbial activity. The most suitable methodology for revegetating with P. lentiscus seedlings was addition of composted residue to soil in conjunction with a mycorrhizal inoculation pretreatment of seedlings in a nursery, to increase available P uptake from composted residue. One year after planting, such a combined treatment had increased the plant height of P. lentiscus seedlings by 106% with respect to the control. [Copyright &y& Elsevier]

To measure P transfers, two small pots, placed 1 cm apart and each containing one leek (Allium porrum L.) plant, were embedded within a larger sand volume. Mesh windows on the facing pot sides allowed the penetration of hyphae but not roots. The effect of earthworms (Aporrectodea caliginosa Sav.) in the hyphal compartment and of arbuscular mycorrhizal fungi (AMF) on plant growth and 32P transfer between plants was investigated. In addition, the effect of mechanical disruption of the hyphal compartment on mycorrhizal plants was studied. AMF did not affect plant growth, although infection levels were high. Earthworms generally increased shoot and root growth; this effect did not appear to be related to location of earthworm activity. 32P transfer from the dying root system of labelled ‘donor’ plants to unlabelled ‘receiver’ plants was increased where earthworm activity was evident between pots, whereas mechanical disruption eliminated the effect of AMF on 32P transfer between mycorrhizal plants. Magnitude of transfer was only related to AMF colonisation levels in the donor plant in the absence of earthworms or mechanical disruption. These results suggest that movement of 32P into the hyphal compartment via the donor AMF mycelium was more important in influencing transfer magnitude than direct transfer via AMF hyphal interconnections between the two plants. Uptake of 32P by the receiver AMF hyphae appears to have been increased by earthworm activity in the hyphal compartment; it is proposed that earthworm-mediated mobilisation of 32P, partly contained within the donor AMF mycelium, led to enhanced 32P availability in the hyphal compartment. [Copyright &y& Elsevier]

Possible interactions between mycorrhiza, atmospheric CO2, free-living soil microorganisms and protozoa were investigated in pot experimental systems. Pea plants (Pisum sativum L. cv. Solara) were grown under ambient (360 μl l−1) or elevated (700 μl l−1) atmospheric CO2 concentration with or without the presence of the arbuscular mycorrhizal (AM) fungus Glomus caledonium. It was hypothesised that (1) the populations of free-living soil protozoa would increase as a response to elevated CO2, (2) the effect of elevated CO2 on protozoa would be moderated by the presence of mycorrhiza and (3) the presence of arbuscular mycorrhiza would affect soil protozoan numbers regardless of atmospheric CO2. After 3 weeks growth there was no difference in bacterial numbers (direct counts) in soil, but the number of free-living bacterial-feeding protozoa was significantly higher under elevated CO2 and was significantly reduced in the mycorrhizal treatments. These effects on protozoa disappeared after 5 and 9 weeks. Neither mycorrhiza nor CO2 concentration had any substantial effect on the microbial community structure as evaluated by phospholipid fatty acid analysis. The increased protozoan populations under elevated CO2 suggest increased bacterial production, whereas the lower populations in response to presence of mycorrhiza suggest a depressing effect on bacterial production by AM colonisation. [Copyright &y& Elsevier]

This study examined the effect of nitrogen fertilization (0, 4 or 8 mmol N added kg−1 soil) on plant growth, nitrate reductase activity (NR) (EC 1.6.6.1) and protein content in Medicago sativa. Plants were inoculated with two strains of Sinorhizobium meliloti [the wild type (WT) strain GR4 and its genetically modified (GM) derivative GR4(pCK3)]. In combination with these inoculations, the arbuscular mycorrhizal (AM) fungus, Glomus mosseae, was compared to a non-mycorrhizal control supplemented with phosphate. The effects of AM on plant growth were greatest when no nitrogen was added to the soil. Nitrogen fertilization reduced these effects according to the S. meliloti strain involved. Growth responses of mycorrhizal plants coinoculated with the GM strain were affected less negatively than those of mycorrhizal plants associated with the WT strain. These results were not related to differential colonization by AM. Increasing nitrogen concentrations reduced mycorrhizal infection and nodule formation was drastically inhibited in mycorrhizal plants by the addition of 4 and 8 mmol N kg−1 soil. Nevertheless, AM symbiosis increased nodule formation in the absence of N fertilization. In non-mycorrhizal plants, however, N fertilizer application did not significantly affect shoot and root growth or nodule formation. Although the P content was higher in P-fertilized, non-mycorrhizal plants than in mycorrhizal ones AM colonization significantly improved P use efficiency. The N content and use efficiency were also highest in mycorrhizal plants. However, the most relevant result regarding NR activity was the varying distributions in mycorrhizal plant shoots and roots as affected by the particular Sinorhizobium strain. The root portion was enhanced by the GM strain, while the WT strain increased the shoot portion. This change in the distribution pattern of root and shoot NR activities was unaffected by N concentrations in the soil. Protein content was substantially higher in mycorrhizal plants. The protein distribution pattern in shoot and root was also highly influenced by mycorrhizal colonization, which enhanced the root portion. Increased nitrogen supply lowered the protein content in both shoot and root tissues. This effect was greatest in AM colonized plants. These results suggest that high N fertilization levels are detrimental to mycorrhizal legume plants. However, under stress conditions (e.g. high N levels) mycorrhizal legumes nodulated by the GM Sinorhizobium strain displayed a physiological response which was better than those nodulated by the WT strain. [Copyright &y& Elsevier]

Lettuce (Lactuca sativa) is a crop with high water and nutrient demand. Its nearest wild relative, Lactuca serriola, is tolerant of low moisture and nutrient-poor conditions. Due to selection in different types of environments, the two taxa may differ in response to mycorrhizal colonization. Pot experiments were used to determine if mycorrhizal colonization, growth, root allocation, and P and N tissue concentrations differed between the two Lactuca taxa when inoculated with Glomus intraradices. In Experiment 1, two levels of P [0 (P0) or 0.25 (P1) mmol P kg−1] were added to a sand/soil medium with and without G. intraradices at low N supply (0.89 mmol N kg−1) for 4 weeks. In Experiment 2, two levels of N [1.7 (N1) or 5.0 (N2) mmol N kg−1] were supplied to the same soils containing 0.25 (P1) mmol P kg−1, and plants were grown for 6 weeks. In Experiment 1, the two taxa had similar mycorrhizal colonization, and shoot and root dry weight. In Experiment 2, cultivated lettuce had slightly higher colonization and growth than wild lettuce. Mycorrhizal plants at N1 were small with high root allocation and colonization. Colonization decreased and growth increased at N2. In these experiments, no major difference in mycorrhizal response occurred between L. sativa and L. serriola. Use of wild lettuce for breeding improved cultivars of lettuce, will at least maintain any ability, to benefit from mycorrhizas, especially in farming systems with low P inputs. [Copyright &y& Elsevier]

Young pitch pine seedlings are frequently subjected to prescribed burns in the New Jersey pine barrens as part of the management to eliminate fuel load in these forests, thereby reducing the risk of wildfire. The burns are relatively cool and release nutrients without killing the vegetation. Not all nutrients mineralized are immediately available to the plants, however. To determine factors that may contribute to nutrient release and to link this to availability of nutrients to plants following a fire in the pine barrens, a greenhouse study was conducted. The experimental design was a 3×2×2×3 factorial with three types of litter, high and low watering regime, burned and unburned litter, and three sample dates. Nitrogen, phosphorus, and potassium (through a rubidium analog) uptake rates were measured using natural isotope or radioisotope root bioassays. Though in the short time the experiment ran, neither an overall burned litter nor a litter quality effect was seen, high watering made P less available and K more available. N and K were the most available immediately following application of treatments, whereas P was not available until after 6 weeks following treatment application. Net mineralization of nitrogen, phosphorus, and potassium occurred in burned litter, whereas net immobilization of N and P occurred in highly watered, unburned litter. Since watering and timing were most influential in making nutrients available to seedlings following application of treatments in this greenhouse study, these factors may also be important in making nutrients available to mature trees in the New Jersey pine barrens. [Copyright &y& Elsevier]

Recent studies on crop rotation have suggested that the cultivation of mycorrhizal host crops increases the arbuscular mycorrhizal (AM) colonization of succeeding crops. A pot experiment was conducted to determine whether the positive effect of AM host cropping on the growth of succeeding maize is mainly due to the multiplication of indigenous AM fungi. Maize plants were grown in soils after mustard (non-host) cropping without AM fungal (AMF) inoculum (MDNI); with inoculum from the soil after sunflower cropping (MDISF); with sterilized inoculum (MDSI); and in the soil after sunflower (host) cropping without inoculum (SFNI). The growth of maize after mustard cropping (MDNI) was inferior to that after sunflower cropping (SFNI). The AMF inoculum from the soil after sunflower cropping (MDISF) improved the growth and AM colonization of maize, and shoot weight was increased from 17 to 49% of that in the SFNI treatment. However, the sterilized inoculum (MDSI) did not show similar effects. Similar AMF species to those increased by sunflower cropping were dominant in SFNI-treated or MDISF-treated soils following maize cropping, also indicating that the AM colonization of maize was improved by multiplied AM fungi through sunflower cropping. These results suggest that the effects of preceding crops on maize growth are at least partly due to differences in AMF density caused by various preceding crops. [Copyright &y& Elsevier]

The effect of the arbuscular mycorrhizal fungus (AMF) Glomus mosseae and the soil-borne Verticillium dahliae and their interaction on root colonization, plant growth and nutrient uptake were studied in eggplant and tomato seedlings grown in pots. It was found that: (a) root colonization by the AMF as well as spore formation was higher (34.6 and 30.5%, respectively) in the eggplant than in tomato. Also it was twice as high in the mycorrhiza treatment than in the treatment with the double inoculation (mycorrhiza+Verticillium); (b) the mycorrhiza treatment increased fresh and dry weight and mean plant height in tomato by 96, 114 and 21% compared to controls. The respective values in eggplant were 114, 104 and 30%; (c) infection by Verticillium reduced fresh weight by 28%, dry weight by 35% and plant height by 14% in tomato. The respective reductions in eggplant were 27, 37 and 12%; (d) the treatment combining both V. dahliae+G. mosseae increased fresh weight by 33%, dry weight by 24% and mean plant height by 21% in tomato. The respective increases in eggplant were 32, 10 and 16%. This leads to the conclusion that the beneficial effect of the AMF supersedes the pathogenic effect of V. dahliae; (e) P and N uptake were higher in mycorrhizal treatments than in controls, although no difference in K, Ca, Mg and B uptake was observed between treatments; (f) mycorrhizal treatments had lower concentrations of micronutrients Zn, Mn, Fe and Cu in shoots and leaves than controls. [Copyright &y& Elsevier]

In a field microcosm experiment, we tested the hypothesis that adult collembola, depending on their density, may enhance or decrease mycorrhizal development and growth of maize (Zea mays L.) or red fescue (Festuca rubra L.). Collembola decreased mycorrhizal spore number in the soil. A significant decrease in the spore number, compared to the treatment without collembola, was recorded and ranged from 0.2 to 1.6 individuals g−1 soil in both experiments. Highest AM fungi colonization was found at 0.2 and 0.4 collembola g−1 soil density in the maize and red fescue treatments, respectively. This finding may explain why about 0.1 individuals g−1 soil was reported as optimum for plant growth by some authors. [Copyright &y& Elsevier]

The effect of an in vitro monoxenically produced arbuscular mycorrhizal fungus (AMF), i.e. Glomus intraradices on the growth and phosphorus content of micropropagated banana (Musa spp. c.v. Grand Naine) plantlets was investigated in a pasteurized and non-pasteurized Vertisol. The experiment was conducted as a 2×2 randomly factorial design with the Vertisol pasteurized or non-pasteurized and the plants inoculated or non-inoculated with the AMF. The plants colonized by AMF had larger shoot and root dry weight and P content than the non-mycorrhizal plants. The largest growth increment was observed in the plants inoculated during the weaning phase with the monoxenic AMF inoculum and subsequently grown in the pasteurized soil. The native AMF population also induced a marked increase in plant growth supporting further the efficiency of this natural population, whereas both inoculum sources in combination did not yield the largest growth increment. The latter suggests a competitive phenomenon between the introduced AMF and the other soil micro-organisms including the native AMF population. Our results demonstrate, for the first time, the potential benefits of a monoxenically produced AMF in micropropagated banana plants. [Copyright &y& Elsevier]

An investigation was carried out to study the influence of arbuscular mycorrhizae (AM) on induction of rooting and other root characteristics of pepper cultivar Panniyur-1. Among three AM fungi tried tested, the maximum percentage rooting was observed in cuttings inoculated with Acaulospora laevis (69.96%). Orthotropic cuttings showed a higher rooting percentage on inoculation with AM. Mycorrhizal inoculation also improved other root characteristics. Among the different AM fungi tried, Gigaspora margarita was efficient in producing the maximum number of primary roots and dry weight of roots, whereas the longest primary root was observed with the inoculation of Glomus fasciculatum. The plant P content was found to be higher in the inoculated plants. It was significantly higher in cuttings inoculated with G. fasciculatum (0.202%). The percentage root colonization and spore count were found to be higher in cuttings inoculated with A. laevis. The present investigation clearly showed the beneficial effects of inoculation with AM fungi which resulted in enhanced rooting and root growth in black pepper cuttings. [Copyright &y& Elsevier]

Selecting indigenous mycorrhizal fungi that enhance plant water status is important in Mexico for sustainable production systems of Chile ancho pepper (Capsicum annuum L. cv. San Luis). To determine mycorrhizal enhancement of drought resistance, plants were either non-inoculated (NonAMF), or inoculated with arbuscular mycorrhizal fungi (AMF): Glomus fasciculatum and a mixed Glomus spp. from Mexico (ZAC-19). Plants were then exposed to a 20-day drought cycle. To equalize growth and minimize tissue-P differences, NonAMF plants received higher P than AMF plants. Drought reduced leaf water potential (Ψleaf), tissue relative water content (RWC), stomatal conductance (gs), whole plant transpiration (mg H2O m−2 s−1), leaf transpirational surface area and plant biomass. Only plants colonized with ZAC-19 had enhanced drought resistance, as indicated by higher Ψleaf and fewest plants with visible wilting during peak drought stress. A higher root/shoot ratio occurred with ZAC-19 plants (despite equal total plant biomass among droughted plants), which may have also contributed to drought resistance. Drought enhanced arbuscule formation and hyphae development of ZAC-19, while reducing colonization of G. fasciculatum. Tissue P was not a contributing factor to drought resistance. AMF did not enhance water-use efficiency (WUE) as-determined gravimetrically on a whole plant basis (g carbon/kg H2O) or by carbon isotope discrimination (Δ). [Copyright &y& Elsevier]

Mycorrhizal associations are essential in the establishment and growth of plant species. The types of mycorrhizas were investigated in the roots of poplar clones introduced in Alberta. We sampled roots of 28 poplar clones from a 5-year old trial established at the Alberta-Pacific Forest Industries Inc. mill site located 40 km North of Boyle, Alberta. The two most common types of mycorrhizas were quantified in plant roots. The poplar clones showed variable degrees of colonization by both ectomycorrhizal and arbuscular mycorrhizal fungi, suggesting differential host susceptibility. This highlights the potential use of selected strains of both ectomycorrhizal and arbuscular mycorrhizal fungi for inoculation trials in populiculture to improve the establishment of introduced poplars on to previously cleared agricultural or disturbed sites in the province of Alberta in particular and in the Canadian prairie provinces in general. [Copyright &y& Elsevier]

The identity and diversity of arbuscular mycorrhizal (AM) fungal symbionts strongly affect the functioning of mycorrhiza, but little is still known about the functional relevance of the individual taxa abundances within AM fungal communities. We hypothesized that proportions of AM fungal taxa influence mycorrhizal benefits to the host, and that a community with spontaneously established ratios of AM fungal species is more beneficial than communities with artificially manipulated ratios. Medic (Medicago truncatula) was inoculated with synthetic AM fungal communities composed of five fungal species in different proportions, and a 'functionally optimized' community generated by previous co-cultivation of the five AM fungi. The composition of the communities was monitored along with the host plant responses to mycorrhiza in three sequential harvests. Most of the artificial AM fungal communities differed compositionally and functionally from the presumably 'functionally optimized' community, which indeed promoted plant growth to the greatest extent. The higher ability to promote plant growth was partly explained by higher intraradical fungal biomass, but functional differences between the communities were also related to the abundances of certain AM fungal species. Thus, the experiment demonstrated functional relevance of species' abundances within AM fungal communities. The observed 'functional optimization' of the AM fungal community is discussed in context with the host plant's and AM fungal species' traits. • Species ratios in mycorrhizal fungal communities influence mycorrhiza functioning. • A spontaneously established mycorrhizal community induced the highest plant benefits. • Manipulation of the fungal species abundances mostly decreased plant benefits. • Fungal species traits explain the differences in the functioning of the communities. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) greatly facilitate uptake of phosphorus (P) by most plant species. Whether or how this changes if water becomes limiting remained little explored. Medicago truncatula plants were grown in previously sterilized cultivation substrate and inoculated or not with AMF isolate Rhizophagus irregularis 'PH5' (M or NM, respectively) in two-compartment rhizoboxes. The compartments were separated or not with root-excluding meshes. A 15-step soil moisture gradient (maintained over 5 weeks) spanned generous water supply through strong water deficiency. Two radioisotopes (33P and 32P) were injected into the plant and distant compartments, respectively, to distinguish cumulative and immediate-term plant P uptake from either of the compartments at each moisture level. M plants were larger than NM plants at high and medium moisture levels and accumulated markedly more P throughout the whole gradient. The immediate-term P uptake did not differ between M and NM plants at high moisture, but at medium and low moistures, M plants acquired significantly more 33P than NM plants, even after accounting for differences in root biomass. Increased immediate-term P uptake by M plants grown under medium and low substrate moistures was probably due to complementary effect of direct hyphal uptake and indirect alterations of substrate hydraulic properties by AMF. This research illustrates that AMF remain functional part of plants even under severe drought stress and thus they should be considered when plant functioning under water deficiency is to be fully understood. • Medicago truncatula plants were inoculated or not with Rhizophagus irregularis. • Mycorrhizal phosphorus uptake was quantified under 15-step moisture gradient. • Radioisotopes enabled to distinguish cumulative and immediate-term phosphorus uptake. • Mycorrhiza increased cumulative phosphorus uptake throughout the whole gradient. • Mycorrhiza increased immediate-term phosphorus uptake at medium and low moistures. [ABSTRACT FROM AUTHOR]

• AMF improved the biomass, nutritional status and oxidative balance of stressed pistachio rootstocks. • AMF decreased the accumulation of Na+ and Cl− in leaves and Na+ in roots of pistachio rootstocks grown under salinity. • The response of the pistachio rootstocks to drought and salinity stresses was different and depends on the stress. • Sarakhs under drought stress, and Badami-Riz–e-Zarand and UCB1 under salinity stress behaved as the most tolerant cultivars. Environmentally-friendly management techniques such as arbuscular mycorrhizal fungi (AMF) strategies are urgently required to improve plant nutrition and overcome abiotic stress. In this study, we evaluated the influence of symbiotic AMF on four pistachio rootstocks subjected to drought (100 % as the control, and 80 %, 60 %, and 40 % of field capacity as the treatments) and salinity (0.91 as the control, and 7.57, 16.12, and 24.63 dS/m using NaCl as the treatments) stress for 60 days in two separate experiments. Under both drought and salinity stress conditions, the root and shoot dry weights of the pistachio rootstocks markedly increased in the AMF-inoculated plants (+M). The accumulation of minerals in the leaves and roots of (+M) plants was significantly higher than in the non-inoculated plants (-M). AMF improved the nutritional status (N, P, Mg2+, and Ca2+) of the genotypes under both stress conditions. Mycorrhizal association significantly decreased Na+ and Cl− concentrations in the leaves and roots of the pistachio rootstocks under salinity stress. In (+M) plants under drought stress, hydrogen peroxide (H 2 O 2) and methylglyoxal (MG) concentrations in leaf and root tissues and malondialdehyde (MDA) in the roots, and under salinity stress, the H 2 O 2 and MG concentrations in the leaves and MDA in both tissues were lower than those in the (-M) plants. The Sarakhs rootstock under salinity stress accumulated lower minerals (N, P, K+, and Ca2+) and more antioxidants than the other rootstocks, which could be due to its higher sensitivity to this stress. Both stresses reduced the chlorophyll concentration and increased the oxidant content and electrolyte leakage from the roots and leaves of the rootstocks. Sarakhs rootstock under drought stress and Badami-Riz–e-Zarand and UCB1 rootstocks under salinity stress behaved better in terms of mineral absorption. Thus, they were more tolerant of drought and salinity stress, respectively. Based on these findings, the association of mycorrhizal fungi and pistachio rootstocks is a sustainable strategy for increasing biomass, mineral, and Chl contents, and decreasing oxidant content, thereby enhancing the stress tolerance of plants. [ABSTRACT FROM AUTHOR]

• Arbuscular mycorrhiza (AM) responsiveness describes the ability of plants to respond to AM with growth or yield differences. • AM responsiveness depends on the plant-fungal genotype combination and on environmental conditions. • The first genetic polymorphism determining quantitative root colonization by AM fungi was identified in rice CERK1. • A new study provides the first estimate of the impact of arbuscular mycorrhiza on maize yield in the field. • Natural variation genetics promises to uncover loci that enable breeding of crops with optimized AM response. Arbuscular mycorrhiza (AM) is an ancient, widespread symbiosis between most land plants and fungi of the Glomeromycotina, which receives increasing interest for agricultural application because it can promote plant growth and yield. The ability of plants to react to AM with changes in morphology and/or performance in terms of yield is called 'AM responsiveness'. Its amplitude depends on the plant- fungal genotype combination and the abiotic and biotic environment. A molecular understanding of AM responsiveness is key for enabling rational application of AM in agriculture, for example through targeted breeding of AM-optimised crops. However, the genetic and mechanistic underpinnings of AM responsiveness variation remain still unknown. Here, we review current knowledge on AM responsiveness, with a focus on agricultural crops, and speculate on mechanisms that may contribute to the variation in AM response. [ABSTRACT FROM AUTHOR]

Stormwater biofilters rely on healthy plant communities to perform essential functions of stormwater management. Mycorrhizae are a class of fungi which may confer benefits to plants growing in green stormwater infrastructure, just as they do in natural ecosystems. Few studies have investigated the roles of mycorrhizae outside natural ecosystems or agricultural systems. This review describes three mechanisms of mycorrhizal symbiosis which could influence plant function in stormwater biofilters. The first mechanism is mycorrhizae acting as an extension of plant roots, providing water and nutrient for plant growth and resistance to stress. Through this mechanism metal removal could also be improved. The second mechanism, mycorrhizal interaction with the rhizosphere, can contribute to soil organic carbon and impact microbial community structures that ultimately affect the N cycle. A third mechanism is discussed in relation to the impact of mycorrhizae on the photosynthetic activity of plants and its subsequent effect on plant growth and resistance to environmental stress. These three mechanisms will be placed into the context of how mycorrhizae could play a crucial role on plant performance and nutrient and metal removal in stormwater biofilters. • Mycorrhizae can enhance pollutant removal in stormwater biofilter • Plant growth can be improved in stormwater biofilter by mycorrhizae • Biofilter plants can increase their stress resistance by mycorrhizal colonisation [ABSTRACT FROM AUTHOR]

• Commercial mycorrhizal fungi increased soil labile P fraction and P concentration in olive tissues. • Mycorrhizal fungi increased soil organic carbon. • Mycorrhizal fungi did not reduce excessive levels of Fe and Mn in shoots. • In this study, commercial mycorrhizal fungi did not increase dry matter yield of potted olive cuttings. • Commercial mycorrhizal fungi should be targeted towards specific purposes rather than for general uses. Biofertilizers of mycorrhizal fungi have been mainly tested in nutrient-limited soils or harsh environmental conditions, which have helped to highlight their beneficial role in plant growth. However, their benefits in stress-free growing conditions have not yet been properly proven. In this work, a commercial mycorrhizal fungi, composed of 18 ecto and endomycorrhizal fungi, was tested in a pot experiment with young olive cuttings, under an experimental apparatus allowing the evaluation of dry matter yield and plant nutritional status after one and two years of growth. The results highlighted the role of the mycorrhiza in increasing P bioavailability, either evaluated by soil P labile fraction or through tissue P concentration. The role of mycorrhiza in increasing soil organic C was also relevant (7% higher than the control). Mycorrhiza had little effect on the uptake of other nutrients and on the alleviation of excessive levels of metals, in particular Fe, in the shoots. Instead, olive showed its own exclusion mechanisms, registering root Fe levels 50 times higher than in shoots. Mycorrhiza did not improve plant growth compared to the other fertilized treatments. The increase in plant dry matter observed in the mycorrhiza treatment in comparison to the control was probably due to the initial content of the commercial product of N, P and K (3% N, 3% P 2 O 5 and 3% K 2 O). Under the conditions of this experiment, the farmer would not benefit from the use of this mycorrhizal fungi, but it nevertheless proved its value for agriculture, suggesting that commercial products should be targeted more towards specific purposes, than for generalized uses. [ABSTRACT FROM AUTHOR]

• Arbuscular mycorrhiza increased essential oil concentration in Ocimum tenuiflorum L. • Eugenol, β-elemene, and β-caryophyllene are major constituents of the essential oil. • Concentration of major compounds was higher in essential oil of mycorrhizal plants. • Mycorrhiza boosted the antioxidant potential of leaves. • The industrial and therapeutic features were improved in the mycorrhizal plants. The increasing interest and demand of Ocimum tenuiflorum L. and its products in different industrial sectors necessitate appropriate cultural practices for cultivation of the plant with increased herbage and essential oil yield. Studies on O. tenuiflorum in relation to arbuscular mycorrhiza are restricted to evaluation of diversity of the mycorrhizal fungi in its rhizosphere or assessment of the ability of different species to colonize its roots. Hence, the present study aimed to assess the effect of arbuscular mycorrhizal fungus (Rhizophagus intraradices) inoculation on the pharmaceutically desired parameters of two high yielding genotypes of O. tenuiflorum. Colonization by R. intraradices fungus resulted in significant increase in the leaf biomass and concentration of essential oil in both the genotypes. Formation of arbuscular mycorrhiza resulted in up to 59.01 % and 86.95 % increase in essential oil concentration in mycorrhizal genotype A and B plants, respectively, in comparison with control. The characterization of essential oils by Gas Chromatography-Mass Spectrometry showed significant effect of arbuscular mycorrhiza on their chemical profile. A total of 23 and 37 compounds were identified in essential oils of control genotype A and B, respectively, while 21 and 34 compounds were detected in essential oils of their respective mycorrhizal counterparts. Concentration of eugenol (a valued phenylpropanoid), and other medicinally important terpenoids (β-elemene, β-caryophyllene, germacrene A, and germacrene D) increased in essential oils of mycorrhizal plants.While genotype and mycorrhizal interaction significantly influenced biomass and essential oil concentration in leaves, the effect of R. intraradices on concentration of eugenol, β-elemene, and β-caryophyllene did not vary between the two genotypes. Additionally, principal component analysis also highlighted that the volatiles common in the essential oil of the four treatments contributed significantly to the variation in the essential oil composition. Phenol, flavonoid, and polyphenol contents in the leaves were also enhanced on formation of arbuscular mycorrhiza. The study also aimed to evaluate the ability of leaves (fresh and processed) to scavenge reactive oxygen and nitrogen species. Arbuscular mycorrhiza augmented the antioxidant capacity of fresh and processed leaves of both the genotypes. Thus, findings of the study demonstrate that R. intraradices inoculation enhances productivity of O. tenuiflorum and also improves the quality of the products. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal (AM) plants and fungi associate with lower soil organic matter, higher pH, lower phosphorus and higher nitrogen than ectomycorrhizal (EM) ones. However, soil conditions correlate with climatic factors, and we suggest that temperature and humidity have also direct roles in the success of mycorrhiza types. The hypothesis here is that EM perform better at low temperatures than AM, and AM resist drought better than EM. Narrowleaf cottonwood (Populus angustifolia E. James) forms both AM and EM. We grew seedlings in soil at 14, 20 and 26 °C in factorial combinations with adequate watering and a cyclic mild drought for 4 and 7 weeks. As hypothesized, the percent of EM root tips was largest at 14 °C, while the proportional root length with AM was largest at the two higher temperatures. However, unlike expectations, drought increased EM formation slightly, while the AM colonization was lower in the dry treatment. Plant growth was reduced more by low temperature than drought. Root branching was more prominent at low temperature and root length and mass growth at higher temperatures. Soil nutrient availability did not provide a direct explanation to the results, as both soluble soil N and P were the same in 14 and 20 °C, while the change in mycorrhiza colonization took place between these temperatures. Differences in root morphology (root branching vs length) may affect the proportions of the mycorrhiza types at different temperature regimes. The most likely explanation to the differential colonization is that temperature affects AM and EM fungi in a different way. In nature, temperature and humidity regimes are tightly correlated, and temperature as such may be a stronger determinant for the success of mycorrhiza types than has been previously considered. The poorer performance of AM in low-temperature and drought conditions may reflect stress avoidance rather than stress tolerance by AM fungi. • Arbuscular mycorrhiza (AM) may resist drought better than ectomycorrhiza (EM). • EM may resist low temperature better than AM. • Drought reduced AM formation but not EM in dual-mycorrhizal Populus angustifolia. • More EM formed at 14 than at 20 and 26 °C, and more AM at 20 and 26 than at 14 °C. • Temperature may be a more important determinant for mycorrhiza than thought before. [ABSTRACT FROM AUTHOR]

Abstract: The aqueous biphasic system (ABS) method using PEG and ammonium sulphate improved the recovery of spores from tropical soils as compared with the sucrose gradient method. The ABS was not affected by low temperatures. The optimal recovery of spores was achieved when 100% PEG and 50% ammonium sulphate concentration and PEG8000 instead of PEG4000 were used. Under these conditions an optimal interface formation which facilitates the localization and recovery of spores was obtained. Both phases of the ABS are aqueous and did not affect either the viability of spores or the level of root colonization reached by these spores. Soil composition did not affect the number of spores obtained by the ABS method either. [Copyright &y& Elsevier]

• Previous studies showed that the vulnerability of mycorrhiza to negative impacts of reactive nitrogen differs in different forests. • In this paper, we introduce a model that explains such differences as resulting from the optimization of belowground tree C investment in forests with inorganic or organic N economy. • The analysis of this model showed that C investment in mycorrhiza did not depend on increasing input of available forms of N into the ecosystem in the case of inorganic N economy (e.g. forests with prevalence of maple on naturally fertile soils). • In contrast, in the case of organic N economy, the model showed decreasing C investment in mycorrhiza with increasing available forms of N (e.g. spruce or pine forests on naturally acid poor soils). • As mycorrhizae are essential for nutrients and water acquisition in trees, we suggest our approach could contribute to predicting the responses of forests to global environmental changes. Elevated reactive nitrogen deposition can result in declines in belowground C allocation to mycorrhiza, potentially threatening the sustainability of forest ecosystems, especially with regard to ongoing global environmental changes. Previous studies showed that the vulnerability of mycorrhiza differs in different forests. In this paper, we introduce a model that explains such differences as resulting from the optimization of belowground tree C investment in forests with inorganic or organic N economy. According to the model, the optimization of belowground tree C investment in forests with organic N economy is governed by indirect competition between trees for available forms of N. We predict decreasing C investment in mycorrhiza with N deposition in systems dominated by an organic N economy. In contrast, in forests with inorganic N economy the optimization of belowground tree C investment is governed by direct competition between trees for available forms of N. We show that C investment in mycorrhiza does not depend on N deposition in the case of inorganic N economy. Parameterizing the model with data from spruce and beech temperate forests, we show that spruce forests are more sensitive to N deposition with a decrease of tree investment in mycorrhiza, which seems to be consistent with empirical findings. As mycorrhizae are essential for nutrients and water acquisition in trees, we suggest our approach could contribute to predicting the responses of forests to global environmental changes. [ABSTRACT FROM AUTHOR]

Total synthesis of Myc-IV(C16:0, S) via automated electrochemical assembly has been accomplished. This tetrasaccharide has been studied as a symbiotic signal molecule of Arbuscular Mycorrhiza fungi. We have achieved stereoselective synthesis of a disaccharide building block using the mixed-electrolyte system for electrochemical glycosylation; 2 + 1+1 strategy enables us to access the tetrasaccharide precursor and complete the synthesis Myc-IV(C16:0, S) efficiently. Image 1 [ABSTRACT FROM AUTHOR]

The concept of soil nutrient availability is still widely viewed within the framework of crop yield responses to fertilizer applications as the intermediary variable linking the rate of application of a single nutrient to the absorption of this nutrient by plants according to the pioneer work of Boussingault (1855), von Liebig (1855), and Mitscherlich (1924). For interpreting the huge variability of crop yield responses to increasing fertilizer applications, agronomists and soil scientists have focused on soil nutrient dynamics in order to estimate the quantity of each nutrient available for plant uptake. This linear approach considering "available nutrient in soil" as an external factor to which plants respond does not correspond to the reality for three main reasons: (i) the root absorption capacity is deeply feed-back controlled by the plant growth capacity itself and, therefore, does not depend univocally on soil nutrient availability; (ii) interactions among different nutrients in soils and plants imply that the availability of one nutrient for plants depends of the availability of others, requiring a more integrated approach; and (iii) the plant itself influences nutrient dynamic processes in soils through interactions with microbial communities in its rhizosphere. Consequently, soil nutrient availability cannot be only considered as a property of the external medium to which plants adapt, but also, and more importantly, as resulting of the functioning of the whole plant-soil-living organisms ecosystem. This review paper proposes an integrated and hypothesis-based vision of plant mineral nutrition based on several recent findings: (i) the corroboration and verification of hypotheses of regulation of plant nutrient uptake at the whole plant level by recent advances in the molecular physiology of plant nutrition, (ii) the physiological basis for interactions among different plant nutrients, and (iii) the increasing evidence of plant-soil interactions at the rhizosphere level. [ABSTRACT FROM AUTHOR]

• Arbuscular mycorrhizal symbiosis promoted a higher concentration of valerenic acid. • Moderated salinity induced valerenic acid production. • Symbiosis improved the growth of valerian plants under salinity stress. • Arbuscular mycorrhizal symbiosis improved ion homeostasis in shoots. • The efficiency of arbuscular mycorrhizal symbiosis was type-dependent. Valerian (Valeriana officinalis L.), which is considered as a medicinal plant, is commonly used in traditional medicine. This study aimed to evaluate the effect of arbuscular mycorrhizal (AM) fungi association under moderate and high salinity stress on growth and physio-biochemical traits of V. officinalis. The bio-ameliorative efficiency of two AM species, Rhizophagus intraradices and Funneliformis mosseae was also compared. The mycorrhizal inoculation generally increased the salt tolerance of plant and positively affected plant growth, P, K+, Mg2+ concentration and the ratios of total chlorophyll: carotenoids, K+: Na+, Ca2+: Na+, and Mg2+: Na+ in shoots compared with those of the non-mycorrhizal plants under saline condition. Moreover, the presence of AM symbiosis mitigated the salinity-induced increase in shoot Na+ concentration, shoot proline, and oxidative damage to membranes. AM fungi considerably promoted root proline and total soluble sugars and total phenolics in shoots and roots versus non-mycorrhizal V. officinalis. Moderate salinity stress increased valerenic acid production, which was more pronounced in F. mosseae inoculated plants. The outcome of the symbiosis was associated with the AM species used, and F. mosseae was more efficient than R. intraradices in the alleviation of salinity stress. This study suggests the potential use of mycorrhizal technology as a practical biotechnological approach to enhance growth and augment bioactive compounds production of V. officinalis in salt-affected soils. [ABSTRACT FROM AUTHOR]