Field Performance and Essential Oil Production of Mycorrhizal Rosemary in Restoration Low‐Nutrient Soils

The establishment and growth of Rosmarinus officinalis L. under field conditions in two low‐nutrient‐content soils were evaluated, as well as the effect of arbuscular mycorrhizal (AM) fungi on essential oil production. The reclamation was conducted in two experimental sites: a limestone quarry and a wasteland soil, both surrounded by Mediterranean vegetation. Mycorrhizal R. officinalis plants inoculated with different AM fungal isolates were used to revegetate the sites. Pre‐transplant inoculation with mycorrhizal fungi resulted in an increased survival of R. officinalis with similar results in both experimental areas. Mycorrhizal inoculation enhanced plant growth, increased essential oil yield and improved the establishment of plants under field conditions. The results indicate that the presence of the symbiosis can accelerate plant growth and alter the biosynthesis of secondary metabolites, thus improving the yield of medicinal plant extracts. It also confirmed the importance of selecting plant/symbiont combinations adapted to the environmental constraints of low‐nutrient‐content soils to design a successful application of mycorrhizal technology in marginal soils. Copyright © 2013 John Wiley & Sons, Ltd.     

Impact of arbuscular mycorrhizal fungi on the growth and expression of gene encoding stress protein – metallothionein BnMT2 in the non‐host crop Brassica napus L.

Arbuscular mycorrhizal (AM) fungi are an important component of the soil biota in most agroecosystems, and their association can directly or indirectly affect the diversity of soil microorganisms, nutrient cycling, and growth of host plants. Since not all crops are symbiotic, we hypothesized that the presence of AM fungi can: (1) inhibit the growth of non‐host plants by resulting in biotic stress, or (2) promote their growth indirectly by increased nutrient mobilization. These hypotheses were tested in the present study on the non‐mycorrhizal crop canola (Brassica napus L.) in the presence and absence of other autochthonous soil microorganisms. The soil was inoculated with a mixture of AM fungi (Acaulospora longula, Glomus geosporum, G. mosseae, Scutellospora calospora) and as a control, a non‐inoculated soil was used. The impact of inoculation on plant growth (biomass production, nutrient concentrations) and expression of the stress protein metallothionein gene BnMT2 was investigated in the shoots. B. napus L. did not form mycorrhizal associations on its roots, but its growth was promoted after inoculation with AM fungi. In the soil with autochthonic microorganisms, growth inhibition after inoculation was observed compared to the control. The concentrations of N, P, K, and S in the shoot were always significantly increased after inoculation with AM fungi. However, this was partly combined with reduced growth and thereby decreased total uptake of nutrients. Expression of BnMT2 in the leaves was increased after inoculation with AM spores at the soil devoid of indigenous microorganisms, but decreased in their presence. The expression of stress proteins (BnMT2) significantly increased with increasing length and biomass of shoots. In conclusion, the inhibition of the non‐host plant B. napus L. following inoculation with AM fungi was confirmed, however, only in combination with autochthonous microorganisms. Growth promotion of B. napus L. in the presence of AM fungi in the absence of autochthonous soil microorganisms suggest that plant growth depression in the presence of AM fungi was based on interactive effects of AM fungi with the autochthonous microorganisms in the soil rather than on a direct impact of the AM fungi.     

Heavy‐metal mobilization and uptake by mycorrhizal and nonmycorrhizal willows (Salix × dasyclados)

Ectomycorrhizal fungi have been shown to affect metal transfer from the soil to the host plant, but the use of these fungi for increased phytoextraction of heavy metals has been scarcely investigated. Therefore, a two‐factorial pot experiment was conducted with Salix × dasyclados and (1) two contaminated soils with different concentrations of NH₄NO₃‐extractable metals and (2) two strains of the ectomycorrhizal fungus Paxillus involutus (one strain originating from a noncontaminated site—Pax1, and another from a contaminated site—Pax2). The inoculation with Pax2 increased the phytoavailability of Cd in the soils. Inoculation with both fungal strains increased the stem and root biomass, but had no effect on metal concentrations in the stems. Decreased Cd and increased Cu concentrations were observed in the roots of inoculated willows. The inoculation with P. involutus increased Cd (up to 22%), Zn (up to 48%), and Cu content in the stems. Decreased Pb content (Cu and Pb content were always <1 mg per plant) occurred in the stems from plants at the soil with the higher concentration of NH₄NO₃‐extractable metals. Contrary to this, in the soil with lower concentrations of NH₄NO₃‐extractable metals, the inoculation had no significant effects on the total uptake of Zn and Cu and even caused decreased Cd (Pax2) and Pb (Pax1) contents in the stems. Strain Pax2 had higher colonization densities, but the plants had lower mycorrhizal dependencies in the contaminated soils than after inoculation with the strain Pax1. Generally, metal extractability in the soils substantially affected the mycorrhizal dependency and heavy‐metal uptake of the willows. We concluded, that the inoculation with P. involutus offers an opportunity to particularly increase the phytoextraction of Zn, but the metal extractability and fungal strain effects have to be tested.     

The application of an organic amendment modifies the arbuscular mycorrhizal fungal communities colonizing native seedlings grown in a heavy-metal-polluted soil

A mesocosm experiment was conducted to investigate whether communities of arbuscular mycorrhizal (AM) fungi associated with roots of native (Piptatherum miliaceum, Retama sphaerocarpa, Psoralea bituminosa, Coronilla juncea, and Anthyllis cytisoides) and for comparison (Lolium perenne) seedlings in a heavy-metal-contaminated, semiarid soil were affected by the application of composted sugar beet waste. We also investigated whether there were relation between AMF diversity and metal concentration (Al, Cd, Cu, Fe, Mn, Pb and Zn) and total P in shoot as well as some soil parameters (total organic carbon and total N) when the SB waste was added to the soil. We analyzed a portion of approximately 795 base pairs of the small-subunit (SSU) rRNA gene by nested PCR, cloning, sequencing, and phylogenetic analyses. Twelve different AMF sequence types were distinguished: seven of these belonged to Glomus group A, one to Glomus group B, one to Diversispora, one to Archaeospora, and two to Paraglomus. The AM fungal populations colonizing roots in a heavy-metal-polluted soil were quite dependent on the host plant, the highest diversity values being obtained in authochtonous plants recognized as metallophytes, such as P. bituminosa, and in an allochtonous, invasive species (L. perenne). No significant correlation was found between AMF diversity and plant metal concentration and soil parameters. Excepting P. bituminosa, when sugar beet waste was added to soil, the populations of AM fungi in roots increased and the shoot metal concentrations decreased in all host plant species studied. Therefore, the addition of sugar beet waste can be considered a good strategy for the remediation and/or phytostabilization of mine tailing sites.     

AM fungi inoculation and addition of microbially‐treated dry olive cake‐enhanced afforestation of a desertified Mediterranean site

A field experiment was carried out to compare the effectiveness of inoculation with three arbuscular mycorrhizal (AM) fungi, namely Glomus intraradices Schenck & Smith, Glomus deserticola (Trappe, Bloss. & Menge) and Glomus mosseae (Nicol & Gerd.) Gerd. & Trappe, and the addition of Aspergillus niger‐treated dry olive cake (DOC) in the presence of rock phosphate, in increasing root nitrate reductase (NR) and acid phosphatase activities, mycorrhizal colonization, plant growth and nutrient uptake in Dorycnium pentaphyllum L. seedlings afforested in a semiarid degraded soil. Three months after planting, both the addition of fermented DOC and the mycorrhizal inoculation treatments had increased root NR activity significantly, particularly the inoculation with G. deserticola (by 75 per cent with respect to non‐inoculated plants), but they had no effect on root acid phosphatase. Mycorrhizal inoculation treatments with G. deserticola or G. mosseae on their own were even more effective than the addition of fermented DOC alone in improving the growth and (NPK) foliar nutrients of D. pentaphyllum plants. The combined treatment involving the application of microbially‐treated agrowastes and mycorrhizal inoculation with AM fungi, particularly with G. mosseae, can be proposed as a successful revegetation strategy for D. pentaphyllum in P‐deficient soils under semiarid Mediterranean conditions. Copyright © 2004 John Wiley & Sons, Ltd.     

Growth and nitrate reductase activity in Juniperus oxycedrus subjected to organic amendments and inoculation with arbuscular mycorrhizae

The effectiveness of reforestation programs on degraded soils in the Mediterranean region is frequently limited by a low soil availability and a poor plant uptake and assimilation of nutrients. While organic amendments can improve the nutrient supply, inoculation with mycorrhizal fungi can enhance plant nutrient uptake. A pot experiment was conducted in 2004 to study the influence of inoculation with an arbuscular mycorrhizal (AM) fungus (Glomus intraradices Schenck & Smith) or with a mixture of three AM fungi (G. intraradices, G. deserticola Trappe, Bloss. & Menge, and G. mosseae (Nicol & Gerd.) Gerd. & Trappe) and of an addition of composted sewage sludge or Aspergillus niger–treated dry‐olive‐cake residue on plant growth, nutrient uptake, mycorrhizal colonization, and nitrate reductase (NR) activity in shoot and roots of Juniperus oxycedrus L. Six months after planting, the inoculation of the seedlings with G. intraradices or a mixture of three AM fungi was the most effective treatment for stimulating growth of J. oxycedrus. There were no differences between the two mycorrhizal treatments. All treatments increased plant growth and foliar N and P contents compared to the control plants. Mycorrhizal inoculation and organic amendments, particularly fermented dry olive cake, increased significantly the NR activity in roots.     

Improved growth and Cu tolerance of Cu excess-stressed white clover after inoculation with arbuscular mycorrhizal fungi

The effects of arbuscular mycorrhizal (AM) fungus, Glomus intraradices, on growth and copper (Cu) tolerance of white clover (Trifolium repens) were investigated in soils with different Cu amounts. The AM inoculation increased plant biomass and the total or bound Cu concentrations in shoots and roots but decreased the total Cu in soils and the exchangeable Cu in shoots, roots and soils at all Cu levels. Mycorrhizal plants had higher levels of root phosphorus and shoot zinc (Zn) at lower Cu levels and more nitrogen and Zn in roots and potassium, calcium and magnesium in shoots and roots at all Cu addition levels. Additionally, AM inoculation enhanced urease, acid phosphatase and catalase activities in rhizosphere soils and mycorrhizal roots showed higher levels of peroxidase, catalase, proline and soluble sugar at all Cu addition levels. These results indicate that mycorrhizal white clover is potentially suitable for Cu phytoremediation based on greenhouse studies.     

Fermentation of sugar beet waste by Aspergillus niger facilitates growth and P uptake of external mycelium of mixed populations of arbuscular mycorrhizal fungi

Sugar beet waste has potential value as a soil amendment and this work studied whether fermentation of the waste by Aspergillus niger would influence the growth and P uptake of arbuscular mycorrhizal (AM) fungi. Plants were grown in compartmentalised growth units, each with a root compartment (RC) and two lateral root-free compartments (RFC). One RFC contained untreated soil while the other RFC contained soil, which was uniformly mixed with sugar beet waste, either untreated (SB) or degraded by A. niger (ASB) in a rock phosphate (RP)-supplied medium. The soil in each pair of RFC was labelled with ³³P and ³²P in order to measure P uptake by the AM fungal mycelium, of which length density was also measured. Whole cell fatty acid (WCFA) signatures were used as biomarkers of the AM fungal mycelium and other soil microorganisms. The amount of biomarkers of saprotrophic fungi and both Gram-positive and Gram-negative bacteria was higher in SB than in ASB treatments. Whilst ASB increased growth and activity of AM mycelium, SB had the opposite effect. Moreover, shoot P content was increased by the addition of ASB, and by inoculation with AM fungi. Modification of soil microbial structure and production of exudates by A. niger, as a consequence of fermentation process of sugar beet waste, could possibly explain the increase of AM growth in ASB treatments. On the other hand, the highest P uptake was a result of the solubilisation of rock phosphate by A. niger during the fermentation.     

Accumulation of Copper,Lead, and Zinc by In Situ Plants Inoculated with AM Fungi in Multicontaminated Soil

Pot and field experiments were conducted to (1) evaluate bioavailability of copper (Cu), lead (Pb), and zinc (Zn) in contaminated soil and phytoremediation potential by in situ plants, B. pilosa var. radiate and Passiflora foetida var. hispida, as inoculated with arbuscular mycorrhizal (AM) fungi, and (2) compare the results of pot and field experiments. The B. pilosa var. radiate plant inoculated with AM fungi had significantly greater Cu concentrations in the shoots and roots than noninoculated plants. Passiflora foetida var. hispida plant inoculated with AM fungi also had significantly greater Cu and Pb concentrations in the roots than noninoculated plants. As the root dry weight of Passiflora foetida var. hispida inoculated with AM fungi dramatically increased, the root Cu, Pb, and Zn content of Passiflora foetida var. hispida inoculated with AM fungi increased by 9–14 times, as compared with the noninoculated plants. The AM fungi have potential to either promote plant growth or increase heavy‐metal accumulation. The values of element translocation proportion from root to shoot were Zn > Cu > Pb for both plant species in pot and field experiments. For both plant species, the results of the pot and field experiments were significantly different. The concentration values of the pot experiment were greater in comparison to the field experiment, and some values were significantly greater than those in the field experiment.     

Establishment of Retama sphaerocarpa L. seedlings on a degraded semiarid soil as influenced by mycorrhizal inoculation and sewage‐sludge amendment

A field experiment was carried out to evaluate the effectiveness of mycorrhizal inoculation with three arbuscular mycorrhizal (AM) fungi (Glomus intraradices Schenck & Smith, Glomus deserticola (Trappe, Bloss. & Menge), and Glomus mosseae (Nicol & Gerd.) Gerd. & Trappe) and the addition of composted sewage sludge (SS) with respect to the establishment of Retama sphaerocarpa L. seedlings, in a semiarid Mediterranean area. Associated changes in soil chemical (nutrient content and labile carbon fractions), biochemical (enzyme activities), and physical (aggregate stability) parameters were observed. Six months after planting, both the addition of composted SS and the mycorrhizal‐inoculation treatments had increased total N content, available‐P content, and aggregate stability of the soil. Values of water‐soluble C and water‐soluble carbohydrates were increased only in the mycorrhizal‐inoculation treatments. Rhizosphere soil from the mycorrhizal‐inoculation treatments had significantly higher enzyme activities (dehydrogenase, protease‐BAA, acid phosphatase, and β‐glucosidase) than the control soil. In the short‐term, mycorrhizal inoculation with AM fungi was the most effective treatment for enhancement of shoot biomass, particularly with G. mosseae (about 146% higher with respect to control plants). The addition of the composted SS alone was sufficient to restore soil structural stability but was not effective with respect to improving the performance of R. sphaerocarpa plants.     

Effect of mixing soil saprophytic fungi with organic residues on the response of Solanum lycopersicum to arbuscular mycorrhizal fungi

The effect of the dual inoculation with arbuscular mycorrhizal (AM) and saprophytic fungi and a combination of wheat straw and sewage sludge residues were studied by determining their effect on dry weight of tomato and on chemical and biochemical properties of soil. Incubation of organic residue (sewage sludge combined with wheat straw) with saprophytic fungi and plant inoculation with mycorrhizal fungi was essential to study plant growth promotion. Soil application of organic residues increased the dry weight of tomato inoculated with Rhizophagus irregularis. The greatest shoot dry mass was obtained when the organic residues were incubated with Trichoderma harzianum and applied to AM plants. However, the greatest percentage of root length colonized with AM in the presence of the organic residues was obtained with inoculation with Coriolopsis rigida. The relative chlorophyll was greatest in mycorrhizal plants regardless of the presence of either saprophytic fungus. The presence of the saprophytic fungi increased soil pH as the incubation time increased. Soil nitrogen and phosphorus contents and acid phosphatase were stimulated by the addition of organic residues, and contents of N and P. Total N and P content in soil increased when the organic residue was incubated with saprobe fungi, but this effect decreased as the incubation period of the residue with saprobe fungi increased. The same trend was observed for soil β‐glucosidase and fluorescein diacetate activities. The application of organic residues in the presence of AM and saprophytic fungi seems to be an interesting option as a biofertilizer to improve plant growth and biochemical parameters of soils.     

Time-course of heavy metal uptake in maize and clover as affected by root density and different mycorrhizal inoculation regimes

A pot experiment was conducted to test the effect of three microbial regimes on the time course of heavy metal uptake in clover and maize from an industrially polluted soil. The three treatments included: (1) an intact flora of bacteria and fungi, including indigenous arbuscular mycorrhizal (AM) fungi together with soil microfauna; (2) the indigenous bacterial/fungal flora except AM fungi, reintroduced into sterilized soil; or (3) the same bacterial/fungal flora plus an AM fungus. For the final harvest, two pot sizes were included to assess the effect of root density. Plant uptake of P and heavy metals varied according to plant species, harvest time and soil treatment. For both plant species, shoot concentration of Zn, Cd and Cu decreased and Ni increased with plant age. Plants growing in sterilized soil with reintroduced AM fungi generally grew better, but contained higher concentrations of heavy metals than those colonized by indigenous AM fungi. Plants with mycorrhiza frequently contained more P, Zn, Cd, Cu and Pb in roots and shoots compared to nonmycorrhizal plants. Elevated root/shoot concentration ratios of P and metals indicate a sequestration of metal phosphates in mycorrhizal roots. Mycorrhizal performance was influenced by root density. At low root densities, metal concentrations in mycorrhizal plants were reduced, whereas it had no effect at high root densities when the entire soil volume was efficiently exploited by roots. We conclude that root density data are essential for interpretations of the influence of AM on metal uptake in plants.     

Variations in nitrogen,zinc, and sugar concentrations in Chinese fir seedlings grown on shrubland and plowed soils in response to arbuscular mycorrhizae-mediated process

One-year-old seedlings of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) are not colonized with ectomycorrhizal (EM) fungi, but often colonized with arbuscular mycorrhizal (AM) fungi. The AM fungi could be important for nutrient acquisition in Chinese fir seedlings. Previous studies show that feedbacks between aboveground and belowground plant tissues play a fundamental role in controlling the interaction between plants and AM fungi. Our results indicate significant feedback in seedlings grown on shrubland soils, but not on plowed soils. The amounts of sugar in fir leaves in the shrubland soils were significantly lower than those in plowed soils. Leaf zinc (Zn) and nitrogen (N) concentrations were significantly higher in seedlings in shrubland soils than in plowed soils. In mycorrhizal seedlings growing in shrubland soils, leaf N:P ratios were significantly higher than those in plowed soils, likely because of enhanced N absorption through AM-mediated process. Leaf N:P ratios in seedlings grown on plowed soils were below the threshold levels, because of low metabolic activity of feedback in AM-mediated process. The results suggested that the presence of feedback between Chinese fir seedlings and AM fungi should be benefit in transplanting Chinese fir seedlings.     

Crop residue and Collembola interact to determine the growth of mycorrhizal pea plants

The effects of collembolan grazing on arbuscular mycorrhizal (AM) fungi and plant growth were studied in a controlled experiment utilizing a mix of AM fungi and the dominant collembolan species (Isotoma sp.) indigenous to the experimental soil. Collembolan (+/– Col) effects were examined in the presence and absence of crop residue (+/– Litter) incorporated into the experimental soil. Significant interactions between collembolans and crop residue occurred for mycorrhizal colonization of roots and plant growth. In the absence of crop residue, collembolans reduced root length colonized by AM fungi, total plant dry mass and seed pod yield. However, in the presence of crop residue, collembolans had no effect on root colonization by AM fungi, and increased total plant mass and pod yield. Crop residue increased root colonization by AM fungi, numbers of bacteria and saprophytic fungi (colony forming units), small- (<5 m) and large- (>5 m) diameter hyphal lengths in soil, and the final population of collembolans in soil. Collembolans reduced both small- and large-diameter hyphae in soil and the number of saprophytic fungi (colony forming units, p =0.052). Feeding preference experiments conducted in vitro showed that Isotoma sp. preferred to graze on mycorrhizal roots over nonmycorrhizal roots when given no other food choice. However, when crop residue was added as a food choice, Isotoma sp. showed a clear feeding preference for crop residue. We conclude that collembolan grazing on mycorrhizae can be detrimental to plant growth when other fungal food sources are limited, but grazing on mycorrhizal fungi does not occur when ample organic matter and associated saprophytic fungi are present in soils.     

Occurrence and infectivity of arbuscular mycorrhizal fungi in some norwegian soils influenced by heavy metals and soil properties

Mycorrhizae are ubiquitous symbiosis which can mediate uptake of some plant nutrients. In polluted soils they could be of great importance in heavy metal availability and toxicity to plants. Mycorrhizae have also been reported to protect plants against toxic metals. We investigated the occurrence and infectivity of arbuscular mycorrhizal (AM) spores as affected by heavy metal levels and other soil properties in Norwegian soils collected from heavy metal polluted, high natural background and non-polluted areas. Spore numbers, mycorrhizal infectivity and spore germination of indigenous mycorrhizal fungi and of a reference strain (Glomus mosseae) in soils showed lower values in two soils with high metal concentrations and in one soil with a low pH. Mycorrhizal infectivity was negatively correlated with extractable metals. Spore number and mycorrhizal infectivity in a soil with naturally high heavy metal content were not different to in non-polluted soils, and indigenous AM fungi appeared more tolerant to metals than those in non-polluted soils. Mycorrhizal infectivity, expressed as MSI₅₀ values, was significantly correlated (r′=0.89, P< 0.05) with the percentage of germinating G. mosseae spores in the soils. However, the number of spores per volume of soil was not significantly correlated with infectivity or spore germination of the reference strain. The spore germination method is discussed as a bioassay of heavy metal toxicity in soil.     

Arbuscular mycorrhizae in a long-term field trial comparing low-input (organic, biological) and high-input (conventional) farming systems in a crop rotation

 Arbuscular mycorrhizal (AM) root colonization was studied in a long-term field trial in which four farming systems currently in use in Switzerland were continuously applied to a randomized set of plots at a single field site from 1978 till 1993. There were two low-input farming systems (organic and bio-dynamic) and two high-input (conventional) farming systems (according to Swiss guidelines of integrated plant production with and without farmyard manure). The systems had an identical 7-year crop rotation and tillage scheme and differed essentially only in the amount and type of fertilizer supplied and in plant protection management. The percentage of root colonization by AM fungi was determined in field samples 2–3 times over the growing season in crops in the rotation, namely in winter wheat (Triticum aestivum L. cv. Sardona), vetch-rye and grass-clover. We found the percentage of root length colonized by AM fungi to be 30–60% higher (P≤0.05) in the plants grown in soils from the low-input farming systems than in those grown in conventionally farmed soils. Approximately 50% of the variation of AM root colonization was explained by chemical properties of the soils (pH, soluble P and K, exchangeable Mg), the effect of soluble soil P being most pronounced. The potential of the field soils from the differently managed plots to cause symbiosis with AM fungi was tested in a glasshouse experiment, using wheat as a host plant. Soils from the low-input farming systems had a greatly enhanced capacity to initiate AM symbiosis. The relative differences in this capacity remained similar when propagules of the AM fungus Glomus mosseae were experimentally added to the soils, although overall root colonization by AM fungi was 2.8 times higher. Received: 27 August 1999     

Uptake of Heavy Metals by Mycorrhizal Barley (Hordeum vulgare L.)

It has been previously indicated that arbuscular mycorrhizal (AM) fungi can enhance the bioremediation abilities of their host plant. Barley (Hordeum vulgare L.) is a crop plant with some unique physiological properties, such as tolerance to salinity. However, its tolerance to other stresses such as heavy metals must be tested. Accordingly, it was hypothesized that barley can be efficiently used to treat heavy metals in symbiotic and non-symbiotic association with AM fungi. In a greenhouse experiment barley plants were inoculated with the AM species Glomus mosseae and grown in a soil polluted with cadmium (Cd), cobalt (Co), and lead (Pb). Relative to Cd and Co, mycorrhizal barley absorbed significantly higher amounts of Pb. AM species also significantly decreased Cd and Co uptake by barley indicating the alleviating effects of G. mosseae on the stress of such heavy metals.     

Effects of hexachlorocyclohexane on rhizosphere fungal propagules and root colonization by arbuscular mycorrhizal fungi in Plantago lanceolata

Lindane ( γ‐hexachlorocyclohexane or γ‐HCH) is an organochlorine insecticide previously used extensively for the control of agricultural pests. We studied the effects of soil HCH contamination on vegetation and its associated arbuscular mycorrhizas (AM). The polluted and unpolluted plots had similar plant cover, with the same species richness and abundance. Plantago lanceolata plants were selected for mycorrhizal analysis because of their presence in both plots and known mycotrophy. The presence of HCH appeared to have no significant effect on the extent of colonization of Plantago roots by AM, suggesting a similar functionality of the fungal symbionts. However, infective AM propagules, the density of AM spores and viable AM hyphae in the rhizosphere were much less in the HCH‐polluted soil than in the unpolluted plot. Pre‐inoculation of four plant species with an isolate of Glomus deserticola obtained from the HCH‐contaminated soil resulted in increased growth and fungal colonization of roots compared with plants pre‐inoculated with the introduced fungus G. macrocarpum or colonized by the consortium of indigenous AM fungal species, when those plants were transplanted to an HCH‐contaminated soil. This suggests that the fungus increases the tolerance of plants to the toxic soil environment. We conclude that herbaceous and woody plants can grow in soil with little P contaminated with <100 mg HCH kg^?1 with the help of tolerant AM, despite the detrimental effect of HCH on AM fungal propagules in soil. The effects of AM fungi on plant growth and soil microbial community structure in HCH‐polluted sites could be important for remediation of the pollutant through the microbial activity in the rhizosphere.     

Colonisation by arbuscular mycorrhizal and fine endophytic fungi in four woodland grasses – variation in relation to pH and aluminium

Acidic soils are harsh environments for plants. One of the major problems is the potential toxicity of aluminium (Al) and hydrogen ions at a pH below 5; another is the shortage of nutrients usually accompanying soil acidity. The aim of this study was to elucidate the relationship between arbuscular mycorrhizal (AM) colonisation and soil acidity (measured by pH and Al concentration) in order to evaluate the possibility that AM fungi facilitate the existence of plants on acidic soils. We sampled tussocks of four grass species, Elymus caninus, Poa nemoralis, Deschampsia cespitosa and Deschampsia flexuosa, together with samples of the surrounding soil, in oak forests of varying soil pH in southern Sweden. We determined pH, easily reacting Al (Al_r), extractable Al (Al_BaCl2) and phosphate in the soil samples, analysed the shoots for Al and phosphorous and quantified the degree of AM and fine endophyte (FE) colonisation in the roots. E. caninus was found on the least acidic soils and had the highest AM colonisation of all the species studied, while D. flexuosa, which was found on the most acidic soils, had the lowest AM colonisation. P. nemoralis and D. cespitosa were intermediate with respect to pH and AM colonisation. The colonisation of AM fungi exceeded FE colonisation for E. caninus and P. nemoralis, while the opposite was true for the two Deschampsia species. Our results indicated a negative relationship between Al_r and the degree of AM colonisation at the within-species level. The low colonisation of AM fungi on acidic soils may to some extent be explained by a sensitivity of AM fungi to Al_r: this parameter showed a stronger negative association with AM colonisation than did pH and Al_BaCl2. We hypothesize that Al toxicity is a critical factor for plant nutrition in forest soils through the impact on symbiotic fungi.     

Increasing the Knowledge on the Management of Cu‐Contaminated Agricultural Soils by Cropping Tomato (Solanum Lycopersicum L.)

This paper increases the knowledge on the potential use of Cu‐contaminated agricultural soils with tomato (Solanum lycopersicum L.). The effect of Cu and its interaction with soil properties on plant biomass production and on the accumulation of this metal in plant tissues were evaluated by conducting biomass assays in four representative Mediterranean agricultural soils contaminated by Cu. Copper toxicity on plant biomass production, evaluated through the effective concentrations of Cu added to soil that reduce the biomass production by 50% (EC₅₀) and by 10% (EC₁₀), was higher in soils having less soil organic matter and clay content and even in soils with favourable properties but having salinity. For the cases in which tomato was collected, Cu concentrations in them were similar for all soils and doses and never exceed the maximum Cu concentration allowed by the Codex Alimentarius Commission Regulation (10 mg_Cu kg⁻¹ in fresh weight basis). According to our results, tomato could be cropped in Cu‐contaminated Mediterranean agricultural soils when concentrations of Cu determined in them rely between their respective EC₅₀ and EC₁₀, because production and quality of fruits, the latter understood as the Cu concentration in them, would not be compromised. For the soils assayed, these values would range between 32·9 and 1696·5 mg kg⁻¹, depending on soil properties. Because the baseline value considered is similar to those established in other parts of the European Mediterranean region, these results can be used as guidance for this region to establish adequate phytoremediation strategies and prevent land degradation processes. Copyright © 2014 John Wiley & Sons, Ltd.