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[Main conclusion]: Rhizobial symbiosis improved the water status of bean plants under salinity-stress conditions, in part by increasing their osmotic root water flow. One of the main problems for agriculture worldwide is the increasing salinization of farming lands. The use of soil beneficial microorganisms stands up as a way to tackle this problem. One approach is the use of rhizobial N2-fixing, nodule-forming bacteria. Salinity-stress causes leaf dehydration due to an imbalance between water lost through stomata and water absorbed by roots. The aim of the present study was to elucidate how rhizobial symbiosis modulates the water status of bean (Phaseolus vulgaris) plants under salinity-stress conditions, by assessing the effects on root hydraulic properties. Bean plants were inoculated or not with a Rhizobium leguminosarum strain and subjected to moderate salinity-stress. The rhizobial symbiosis was found to improve leaf water status and root osmotic water flow under such conditions. Higher content of nitrogen and lower values of sodium concentration in root tissues were detected when compared to not inoculated plants. In addition, a drop in the osmotic potential of xylem sap and increased amount of PIP aquaporins could favour higher root osmotic water flow in the inoculated plants. Therefore, it was found that rhizobial symbiosis may also improve root osmotic water flow of the host plants under salinity stress.

A pot experiment was designed to evaluate the interactive effects of multiple microbial inoculation treatments and rock phosphate (RP) application on N and P acquisition by alfalfa plants using 15N and 32P isotopes. The microbial inocula consisted of a wild type (WT) Rhizobium meliloti strain, its genetically modified (GM) derivative, which had an enhanced competitiveness, the arbuscular mycorrhizal (AM) fungus Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe, and a phosphate-solubilizing rhizobacterium (Enterobacter sp.). Inoculated micro-organisms became established in the root tissues and/or in the rhizosphere soil of alfalfa plants (Medicago sativa L.). The GM Rhizobium strain did not interfere with AM formation. Inoculated phosphate-solubilizing rhizobacteria established in the alfalfa rhizosphere, but the level of establishment was lower where the natural population of phosphate-solubilizing bacteria was stimulated by AM inoculation and RP application. The stimulation of these indigenous bacteria was also greater in the rhizosphere of alfalfa nodulated by the GM Rhizobium. Improvements in N and P accumulation in alfalfa corroborate beneficial effects of the improved GM Rhizobium on AM performance, in RP-amended plants. Inoculation with Enterobacter did not improve the AM effect on N or P accumulation in the RP-added soil, but it did in the non RP-amended controls. Measurements of the 15N∶14N ratio in plant shoots indicated enhanced N2 fixation rates in Rhizobium-inoculated AM-plants, over that achieved by the same Rhizobium strain in non-mycorrhizal plants. Regardless of the Rhizobium strain and of whether or not RP was added, AM-inoculated plants showed a lower specific activity (32P∶31P) than did their comparable non-mycorrhizal controls, suggesting that the plant was using otherwise unavailable P sources. The phosphate-solubilizing, AM-associated, microbiota could in fact release phosphate ions, either from the added RP or from the indigenous ‘less-available’ phosphate. Deficiency in Ca concentration in soil solution in the neutral test soil might benefit P solubilization. The proportion of plant P derived either from the labelled soil P (labile P pool) or from RP was similar for AM inoculated and non-mycorrhizal controls (without Enterobacter inoculation) for each Rhizobium strain, but the total P uptake, regardless of the P source, was far higher in AM-plants. Enterobacter inoculation seems to improve the use of RP in the rhizosphere of non-mycorrhizal plants inoculated with the WT Rhizobium., The authors thank the EC Biotechnology Programme, IMPACT Project BIO4-CT96-0027.

Yeasts are abundant and diverse in rhizosphere soil, but information about their importance in agroecosystems is limited. Here we examined maize plant growth response to inoculation with the native maize rhizosphere yeasts Cryptococcus flavus and Candida railenensis in non-mycorrhizal and mycorrhizal maize without and with mineral P fertilization as KH2PO4. Maize plant growth promotion and suppression was observed after inoculation with a native community of arbuscular mycorrhizal (AM) fungi with and without mineral P fertilization, respectively. Inoculation with Cr. flavus reduced shoot biomass of maize plants irrespective of the mycorrhizal status, but only without P fertilization. AM fungal root colonization was increased by C. railenensis without P fertilization, but was reduced by Cr. flavus in combination with mineral P fertilization. In conclusion, our results show that mineral P fertilization strongly modulates interactions between maize, rhizosphere yeasts and AM fungi, which are important to take into account when integrating such root associated microorganisms as biofertilizers in agroecosystems., This study was supported with the grant 179319 from Consejo Nacional de Ciencia y Tecnología (CONACYT). Marcela Sarabia was supported with the Ph.D. fellowship 239182 also from CONACYT.

Sulla carnosa (Hedysarum carnosum Desf.) is an important legume grown as animal feed on salt-affected areas. Here, we assess the influence of plant-growth-promoting bacteria (PGPR) (Bacillus subtilis) with or without the mycorrhizal fungus (AMF) Rhizophagus intraradices on four S. carnosa Tunisian provenances (Sidi khlif, Thelja, Kalbia and Kerker) grown in the greenhouse under saline and non-saline conditions. Plant growth, mineral nutrition, C:N:P stoichiometry in plant shoots, and soil enzymatic activities were considered. Microbial effectiveness on plant (roots and shoots) growth ranged from insignificant in Kerker to highly positive in the provenances Sidi khlif and Kalbia. In the latter provenance, the positive effect on growth was more pronounced under dual than single inoculation. Plant growth declined significantly under salt stress compared to the control, but Sidi khlif provenance was the most severely impacted. Especially in Kalbia, shoot mineral (N, P, K, Mg, Cu, and Fe) concentrations increased significantly in salt-stressed plants inoculated with R. intraradices as compared to the salt-stressed and non-inoculated plants. This suggests that inoculation with R. intraradices during nursery establishment contributes to salt stress alleviation by maintaining a favourable nutrient profile in Kalbia provenance. Shoots of Sidi khlif plants inoculated with B. subtilis demonstrated distinct C:N:P stoichiometry as compared to salt-treated and non-inoculated plants, indicating that B. subtilis could increase plant tolerance to salt stress through nutrient allocation patterns. The efficiency of B. subtilis in Kalbia and Thelja was due to the high IAA production by this strain under stress conditions. Application of PGPR and AMF improved soil quality by increasing the activities of soil enzyme such as urease, alkaline phosphatase, β-glucosidase and dehydrogenase compared to their respective non-inoculated controls. From this study, we conclude that microbial inoculation was necessary for S. carnosa provenances to reach their optimal nutrition under saline and non-saline conditions. Thus, the use of adequate microbial inocula and provenance could be a critical issue for the successful ecological stability of this Mediterranean legume, thereby improving its suitability for the remediation of saline lands., This work was carried out in the framework of project AGL2009-12530-C02-02 from Ministry of Economy and Competitiveness (Spain) and supported by the Tunisian Ministry of Higher Education and Scientific Research (LR10CBBC02), for a stay at the Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, CSIC, Granada, Spain.

7 páginas.- 3 imagenes.- 2 tablas.- 45 referencias.-- Supplementary data related to this article can be found at https://doi.org/10.1016/j.plaphy.2019.04.017, Olive trees are known for their capacity to adapt to drought through several phenotypic and molecular variations, although this can vary according to the different provenances of the same olive cultivar. We confronted the same olive cultivar from two different location in Spain: Freila, in the Granada province, with low annual precipitation, and Grazalema, in the Cadiz province, with high annual precipitation, and subjected them to five weeks of severe drought stress. We found distinctive physiological and developmental adaptations among the two provenances. Thus, trees from Freila subjected to drought stress exhibited increasing root dry weights and decreasing leaf numbers and relative stem heights. On the other hand, the treatment with drought in Grazalema trees reduced their leaf chlorophyll contents, but increased their relative stem diameter and their root hydraulic conductivity. The physiological responses of Freila tree roots to drought were linked to different molecular adaptations that involved the regulation of genes related to transcription factors induced by ABA, auxin and ethylene signaling, as well as, the action of a predicted membrane intrinsic protein (MIP). On the other hand, the responses of Grazalema trees were related with different root genes related to oxidation-reduction, ATP synthesis, transduction and posttranslational regulation, with a special mention to the cytokinins signaling through the transcript predicted as a histidine-containing phosphotransfer protein. Our results show that olive trees adapted to dry environments will adjust their growth and water uptake capacity through transcription factors regulation, and this will influence the different physiological responses to drought stress., The study was supported by the Junta de Andalucía through the research project P10-CVI-5920

Salt stress has become a major menace to plant growth and productivity. The main goal of this study was to investigate the effect of inoculation with the arbuscular mycorrhizal fungi (AMF; Rhizophagus intraradices) in combination or not with plant growth‐promoting rhizobacteria (PGPR; Pseudomonas sp. (Ps) and Bacillus subtilis) on the establishment and growth of Sulla coronaria plants under saline conditions. Pot experiments were conducted in a greenhouse and S. coronaria seedlings were stressed with NaCl (100 mM) for 4 weeks. Plant biomass, mineral nutrition of shoots and activities of rhizosphere soil enzymes were assessed. Salt stress significantly reduced plant growth while increasing sodium accumulation and electrolyte leakage from leaves. However, inoculation with AMF, whether alone or combined with the PGPR Pseudomonas sp. alleviated the salt‐induced reduction of dry weight. Inoculation with only AMF increased shoot nutrient concentrations resulting in higher K+: Na+, Ca2+: Na+, and Ca2+: Mg2+ ratios compared to the non‐inoculated plants under saline conditions. The co‐inoculation with AMF and Pseudomonas sp. under saline conditions lowered shoot sodium accumulation, electrolyte leakage and malondialdehyde (MDA) levels compared to non‐inoculated plants and plants inoculated only with AMF. The findings strongly suggest that inoculation with AMF alone or co‐inoculation with AMF and Pseudomonas sp. can alleviate salt stress of plants likely through mitigation of NaCl‐induced ionic imbalance, thereby improving the nutrient profile., This work was carried out in the framework of Project AGL 2009-12530-C02-02 from Ministerio de Economía y Competitividad (Spain) and supported by the Tunisian Ministry of Higher Education and Scientific Research (LR10CBBC02), for a stay at the Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, CSIC, Granada, Spain.

Selenium (Se) is an important antioxidant considered among the fertilization programs in developed countries. In Chile, chemical fertilization based in Se is inefficient due the physicochemical characteristics of Andisol that sustain the 60% of crop production. Andisol also are highly conductive to take-all disease caused by Gaeuman-nonyces graminis var tritici (Ggt). Here, we evaluated the effect of Bacillus sp.E5 and Acinetobacter sp.E6.2 and Claroideoglomus claroideum as potential inocula for Se biofortification and Ggt bicontrol in wheat. Plants inoculated with Acinetobacter sp.E6.2 showed major root growth and major Se content in shoots and grains. The antioxidant role of Se regarding DPPH activity was shown in Se-supplemented plants with small Se nanoparticles founded inside the roots. Mycorrhizal plants showed major SOD activity in shoots but no affected the Se uptake. Respect to pathogen biocontrol, plants inoculated with both bacteria showed an efficient control against Ggt independent to mycorrhization. Thus, our inocula could make important contributions to produce enriched Se flours for human nutrition and biocontrol against Ggt., This study was supported by the Comisión Nacional de Investigación Científica y Tecnológica (CONICYT), FONDECYT Postdoctoral Project N° 3130542 and FONDECYT Iniciation Project No. 11150540 from Chilean Government.

The adaptation capacity of olive trees to different environments is well recognized. However, the presence of microorganisms in the soil is also a key factor in the response of these trees to drought. The objective of the present study was to elucidate the effects of different arbuscular mycorrhizal (AM) fungi coming from diverse soils on olive plant growth and water relations. Olive plants were inoculated with native AM fungal populations from two contrasting environments, that is, semi-arid - Freila (FL) and humid - Grazalema (GZ) regions, and subjected to drought stress. Results showed that plants grew better on GZ soil inoculated with GZ fungi, indicating a preference of AM fungi for their corresponding soil. Furthermore, under these conditions, the highest AM fungal diversity was found. However, the highest root hydraulic conductivity (Lpr ) value was achieved by plants inoculated with GZ fungi and growing in FL soil under drought conditions. So, this AM inoculum also functioned in soils from different origins. Nine novel aquaporin genes were also cloned from olive roots. Diverse correlation and association values were found among different aquaporin expressions and abundances and Lpr , indicating how the interaction of different aquaporins may render diverse Lpr values.

This study evaluates the responses of Lavandula dentata under drought conditions to the inoculation with single autochthonous arbuscular mycorrhizal (AM) fungus (five fungal strains) or with their mixture and the effects of these inocula with a native Bacillus thuringiensis (endophytic bacteria). These microorganisms were drought tolerant and in general, increased plant growth and nutrition. Particularly, the AM fungal mixture and B. thuringiensis maximized plant biomass and compensated drought stress as values of antioxidant activities [superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase APX)] shown. The AMF-bacteria interactions highly reduced the plant oxidative damage of lipids [malondialdehyde (MDA)] and increased the mycorrhizal development (mainly arbuscular formation representative of symbiotic functionality). These microbial interactions explain the highest potential of dually inoculated plants to tolerate drought stress. B. thuringiensis “in vitro” under osmotic stress does not reduce its PGPB (plant growth promoting bacteria) abilities as indole acetic acid (IAA) and ACC deaminase production and phosphate solubilization indicating its capacity to improve plant growth under stress conditions. Each one of the autochthonous fungal strains maintained their particular interaction with B. thuringiensis reflecting the diversity, intrinsic abilities and inherent compatibility of these microorganisms. In general, autochthonous AM fungal species and particularly their mixture with B. thuringiensis demonstrated their potential for protecting plants against drought and helping plants to thrive in semiarid ecosystems., E. Armada was financed by Ministry of Science and Innovation (Spain). This work was carried out in the framework of the project reference AGL2009-12530-C02-02.

[Background]: New evidence has shown that arbuscular mycorrhizal (AM) fungi can contribute to the aluminum (Al) tolerance of host plants growing in acidic soils with phytotoxic levels of Al. The aim of this study was to investigate the role of AM fungi isolated from naturally occurring Al acidic soils in conferring host tolerance to Al toxicity in three wheat cultivars differing in Al sensitivity. The experiment was conducted in a soilless substrate (vermiculite/perlite, 2:1 v/v) using two Al-tolerant wheat genotypes and one Al-sensitive wheat genotype. The wheat was colonized with a consortium of AM fungi isolated from an Andisol, with or without Al at a concentration of 200 μmol L., [Results]: The response of wheat to Al in the medium was dependent on both the plant genotype and AM colonization. The benefits of the AM fungi to the wheat cultivars included an increased P concentration and relatively low Al accumulation in the plants. This was achieved through two mechanisms. First, the metal-chelating capacity of the AM fungi was clear in two of the cultivars (‘Tukan’ and ‘Porfiado’), in which the enhanced extraradical mycelium development was able to retain Al in the glomalin and hyphae. Second, the increased AM-induced acid phosphatase activity in the rhizosphere of the other cultivar (‘Atlas 66’) increased host nutrition possibly by hyphae-mediated nutrient uptake and glomalin-related soil protein., [Conclusion]: The results suggest that the role of AM fungi in cultivar-specific Al detoxification can be achieved by increased extraradical mycelial filters and enhanced bioavailability of P in the host rhizosphere., This study was supported by FONDECYT 11160385 (A Seguel) grant from the Comisión Nacional de Investigación Científica y Tecnológica (CONICYT), Chile. A Valentine was supported in Chile by a grant from the MEC Program 80170023 (CONICYT).

Inoculation of plants with beneficial plant growth-promoting bacteria (PGPB) emerges a valuable strategy for ecosystem recovery. However, drought conditions might compromise plant-microbe interactions especially in semiarid regions. This study highlights the effect of native PGPB after 1 year inoculation on autochthonous shrubs growth and rhizosphere microbial community composition and activity under drought stress conditions. We inoculated three plant species of semiarid Mediterranean zones, Thymus vulgaris, Santolina chamaecyparissus and Lavandula dentata with a Bacillus thuringiensis strain IAM 12077 and evaluated the impact on plant biomass, plant nutrient contents, arbuscular mycorrhiza fungi (AMF) colonization, soil rhizosphere microbial activity and both the bacterial and fungal communities. Inoculation with strain IAM 12077 improved the ability of all three plants species to uptake nutrients from the soil, promoted L. dentata shoot growth (> 65.8%), and doubled the AMF root colonization of S. chamaecyparissus. Inoculation did not change the rhizosphere microbial community. Moreover, changes in rhizosphere microbial activity were mainly plant species-specific and strongly associated with plant nutrients. In conclusion, the strain IAM 12077 induced positive effects on plant growth and nutrient acquisition with no impact on the rhizosphere microbiome, indicating a rhizosphere microbial community resilient to native bacteria inoculation., E. Armada was financed by the Ministry of Science and Innovation, Spain. This work was carried out in the framework of the project reference AGL2009-12530-C02-02 with a grant of short stay (ref. BES-2010-042736) at NIOO-KNAW in Wageningen, and the grant The Netherlands Organization for Scientific Research (NWO, 729.004.016), M.F.A. Leite was financed by CAPES A116-2013 program.

Selenium (Se) is an important micronutrient for human health especially to fortifying the immune system. Chilean Andisols contain low quantities of Se and we have shown that bacteria can be used to enhance Se content of food plants and to improve the antioxidant system against different abiotic stresses. In this study, we prepared inocula based on previously selected Se tolerant endophytic bacteria (Acinetobacter sp. E6.2 and Bacillus sp. E5), which were supplemented with sodium selenite at 5 mM. We studied the effect of this Se amount on bacterial synthesis of organic compounds and Se toxicity, NanoSe size, together with the role of Se in drought stress mitigation. Our results indicated that Acinetobacter sp. E6.2 produced elevated quantities of seleno-methionine (SeMet) and seleno-methyl-selenocysteine (SeMeSeCys) (10 and 3.77 mg kg−1, respectively). However, highly stable NanoSe (Z potential around −40 mV) was the main Se form found in both inocula. The size of NanoSe in Acinetobacter sp. was greater than in Bacillus sp. over time (i.e. 213 ± 3.4 nm and 169 ± 0.92 nm, respectively at 24 h). Bacteria selenium supplementation did not induce oxidative stress due to similar superoxide dismutase (SOD) and catalase (CAT) activities. Selenium did not affect cell tolerance to water deficit due to similar proline and indole acetic acid (IAA) production under drought stress conditions. The findings of this study suggest that these new endophytic bacteria inocula could be effective for Se biofortification., This study was supported by the Comisión Nacional de Investigación Científica y Tecnológica (CONICYT), FONDECYT Postdoctoral Project No. 3130542 from Chilean Government. The authors also acknowledge the technical support by Scientific and Technological Bioresource Nucleus (BIOREN) from Universidad de la Frontera and Horacio Miranda for his collaboration in date analyses.

Studies have shown that some microorganisms autochthonous from stressful environments are beneficial when used with autochthonous plants, but these microorganisms rarely have been tested with allochthonous plants of agronomic interest. This study investigates the effectiveness of drought-adapted autochthonous microorganisms [Bacillus thuringiensis (Bt) and a consortium of arbuscular mycorrhizal (AM) fungi] from a degraded Mediterranean area to improve plant growth and physiology in Zea mays under drought stress. Maize plants were inoculated or not with B. thuringiensis, a consortium of AM fungi or a combination of both microorganisms. Plants were cultivated under well-watered conditions or subjected to drought stress. Several physiological parameters were measured, including among others, plant growth, photosynthetic efficiency, nutrients content, oxidative damage to lipids, accumulation of proline and antioxidant compounds, root hydraulic conductivity and the expression of plant aquaporin genes. Under drought conditions, the inoculation of Bt increased significantly the accumulation of nutrients. The combined inoculation of both microorganisms decreased the oxidative damage to lipids and accumulation of proline induced by drought. Several maize aquaporins able to transport water, CO2 and other compounds were regulated by the microbial inoculants. The impact of these microorganisms on plant drought tolerance was complementary, since Bt increased mainly plant nutrition and AM fungi were more active improving stress tolerance/homeostatic mechanisms, including regulation of plant aquaporins with several putative physiological functions. Thus, the use of autochthonous beneficial microorganisms from a degraded Mediterranean area is useful to protect not only native plants against drought, but also an agronomically important plant such as maize., E. Armada was financed by Ministerio de Economía y Competitividad (Spain) (BES-2010-042736). This work was carried out in the framework of the project reference AGL2012-39057-C02.

The sustainability and productivity of agroecosystems depends exquisitely on the functionality of a framework of plant–soil interactions where microbial populations, including both mutualistic symbionts and saprophytic microorganisms, living at the root–soil interfaces, the rhizosphere, are involved. Among various beneficial and consumable plant species, legumes form useful symbiotic relationships with two types of soil microbiota: N2-fixing bacteria, often called rhizobia, and arbuscular mycorrhizal (AM) fungi. Also, the legume rhizosphere inhabits other valuable microbes such as plant growth-promoting rhizobacteria (PGPR). These microorganisms interact intensely among themselves, and with legume roots, to develop the multifunctional legume mycorrhizosphere, a microcosm environment of variable activities, appropriate for legume productivity. This chapter highlights (1) the types of microorganisms and processes involved in the establishment and functioning of the mycorrhizosphere, (2) the impact of the mycorrhizosphere activities on legume production, and (3) the possibilities to tailor an efficient mycorrhizosphere as a biotechnological tool to improve legume performance in different production systems following efficient rhizobial, PGPR, and AM fungal inoculants., This research was supported by the Andalusian Research Programme (Project CVI-7640) and the Spanish National Research Programme (R & D)-European Union (Feder) (Project CGL2015-69118-C2-2-P).

Cereal crops grown in southern Chilean Andisol provide suboptimal levels of this metalloid for human diet. Certain rhizosphere microorganisms, such as rhizobacteria and arbuscular mycorrhizal fungi can increase the selenium uptake in plants. The purpose of this study was to evaluate selenium acquisition by wheat plants through the co-inoculation of native selenobacteria strains (Stenotrophomonas sp. B19, Enterobacter sp. B16, Bacillus sp. R12 and Pseudomonas sp. R8), both individually and in mixture, as selenonanosphere source with one arbuscular mycorrhizal fungus (Glomus claroideum). Total selenium content in plant tissues and substrate was analyzed. According to our results, significant higher selenium content was found in inoculated plants in comparison to uninoculated controls (P ≤ 0.05). Independently of fungal presence, selenium content in grain from plants inoculated with Enterobacter sp. B16 (236 mg kg−1) was higher than the rest of the strains (116–164 mg kg−1). However, when plants were co-inoculated with a mixture of selenobacteria strains and G. claroideum, selenium content in grain was 23.5% higher (725 mg kg−1) than non-mycorrhizal plants (587 mg kg−1). The results suggest a synergistic effect between the selenobacteria mixture and G. claroideum associated to major biodiversity and demonstrate a great potential of these rhizosphere microorganisms for biofortification of cereals and its derivates., This study was supported by CONICYT Postdoctoral scholarship 3130542 and FONDECYT 1100625 of the Chilean Government. J.J. Acuña is thankful for the financial support of CONICYT through the Doctoral Fellowship Program. M.A. Jorquera also acknowledges financial support by FONDECYT 1120505.

The recovery of species composition and functions of soil microbial community of degraded lands is crucial in order to guarantee the long-term self-sustainability of the ecosystems. A field experiment was carried out to test the influence of combining fermented sugar beet residue (SBR) addition and inoculation with the arbuscular mycorrhizal (AM) fungus Funneliformis mosseae on the plant growth parameters and microbial community composition and function in the rhizosphere of two autochthonous plant species (Dorycnium pentaphyllum L. and Asteriscus maritimus L.) growing in a semiarid soil contaminated by heavy metals. We analysed the phospholipid fatty acids (PLFAs), neutral lipids fatty acids (NLFAs) and enzyme activities to study the soil microbial community composition and function, respectively. The combined treatment was not effective for increasing plant growth. The SBR promoted the growth of both plant species, whilst the AM fungus was effective only for D. pentaphyllum. The effect of the treatments on plant growth was linked to shifts in the rhizosphere microbial community composition and function. The highest increase in dehydrogenase and β-glucosidase activities was recorded in SBR-amended soil. The SBR increased the abundance of marker PLFAs for saprophytic fungi, Gram+ and Gram− bacteria and actinobacteria, whereas the AM fungus enhanced the abundance of AM fungi-related NLFA and marker PLFAs for Gram− bacteria. Measurement of the soil microbial community composition and function was useful to assess the success of phytomanagement technologies in a semiarid, contaminated soil., This research was supported by the Spanish Ministry of Economy and Competitiveness (Project AGL2012-39057-CO2-01).

Bacteria (Pseudomonas sp. and Bacillus sp.) and/or the arbuscular mycorrhizal (AM) fungus Rhizophagus intraradices were able to improve growth, physiological and biochemical characteristics of four Sulla carnosa Desf. provenances (Sidi khlif, Thelja, Kalbia and Kerker) from Tunisia under both saline and non-saline conditions. S. carnosa is a salt-tolerant legume plant, native from North Africa. The intrinsic bacterial characteristics evidenced the fitness of these bacteria to support salt stress and to stimulate plant growth. Bacillus sp. produced more indol acetic acid (IAA) than Pseudomonas sp. and showed a great surviving capacity under salt conditions supporting its capacity to improve plant growth under stress conditions. The microorganisms applied also have a different potential to increase the nutritional and related plant growth parameters. It is noticeable that some provenances reached the highest level of growth when inoculated with Bacillus sp. in Sidi khlif or by Bacillus plus AMF in Kalbia, which increased shoot by 318% and root by 774%. In contrast, in Thelja and Kerker the impact of the test microorganisms was mainly evidenced at increasing nutritional and physiological functions. Salinity reduced some growth and physiological variables as stomatal conductance, photosynthetic pigments and photosynthetic efficiency and increased electrolyte leakage. However, the microbial inoculants compensated these detrimental effects in a degree depending on the S. carnosa provenance. These microorganisms also orchestrate antioxidant activities involved in adaptative responses in S. carnosa provenances. The intrinsic ability of inoculants allow us to select the provenance/microorganism combination which maximizes S. carnosa growth, nutrition and physiological/biochemical responses under salt and non-salt conditions. The results obtained support that the target microbial inocula are beneficial for the ecological stability if this Mediterranean legume., This work was carried out in the framework of project AGL2009-12530-C02-02 from Ministerio de Economía y Competitividad (Spain). Hidri Rabaa was financed by the Tunisian Ministry of Higher Education and Scientific Research (LR10CBBC02), for a stay at the Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, CSIC, Granada, Spain.

This study evaluated the co-inoculation effect of the endophytic selenobacteria Bacillus sp., Klebsiella sp. or Acinetobacter sp. and the arbuscular mycorrhizal (AM) fungus Rhizophagus intraradices on lettuce plants grown under drought conditions. Plants inoculated with bothnmicroorganisms were able to enhance the Se content in their shoots (1 to 6 pg plant-1) and promote macro-and micronutrient uptake. Moreover, the inoculated plants showed significantntolerance to drought stress, as determined by their adaptation to physiological parameters(relative water content and stomatal conductance), increase in photosynthetic pigments (chlorophyll and carotenoids) and improvement inantioxidant enzyme levels (catalase, ascorbate peroxidase and glutathione reductase). The selenobacteria increased the Se content in lettuce plants and enhanced the effect of AM fungus in controlling the antioxidant systems that play a role as elicitors of plant drought responses and improving the nutritional quality and physiological and biochemical processes involved in plant drought tolerance., This study was supported by the Comisión Nacional de Investigación Científica y Tecnológica (CONICYT), FONDECYT Postdoctoral Project N° 3130542 from the Chilean Government and project reference AGL2009-12530-C02-02 (Spain Government). E. Armada was financed by the Ministry of Science and Innovation (Spain).

Rice is a salt-sensitive crop whose productivity is strongly reduced by salinity around the world. Plants growing in saline soils are subjected to the toxicity of specific ions such as sodium, which damage cell organelles and disrupt metabolism. Plants have evolved biochemical and molecular mechanisms to cope with the negative effects of salinity. These include the regulation of genes with a role in the uptake, transport or compartmentation of Na and/or K. Studies have shown that the arbuscular mycorrhizal (AM) symbiosis alleviates salt stress in several host plant species. However, despite the abundant literature showing mitigation of ionic imbalance by the AM symbiosis, the molecular mechanisms involved are barely explored. The objective of this study was to elucidate the effects of the AM symbiosis on the expression of several well-known rice transporters involved in Na/K homeostasis and measure Na and K contents and their ratios in different plant tissues. Results showed that OsNHX3, OsSOS1, OsHKT2;1 and OsHKT1;5 genes were considerably upregulated in AM plants under saline conditions as compared to non-AM plants. Results suggest that the AM symbiosis favours Na extrusion from the cytoplasm, its sequestration into the vacuole, the unloading of Na from the xylem and its recirculation from photosynthetic organs to roots. As a result, there is a decrease of Na root-to-shoot distribution and an increase of Na accumulation in rice roots which seems to enhance the plant tolerance to salinity and allows AM rice plants to maintain their growing processes under salt conditions., This work was financed by a research project supported by Junta de Andalucía (Spain). Project P11-CVI-7107

The aim of this study was to assess the effectiveness of inoculation with a native arbuscular mycorrhizal (AM) fungus, Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe, or a filamentous fungus, Penicillium aurantiogriseum Dierckx 1901, on the establishment of Coronilla juncea L. seedlings grown in a polluted, semiarid soil. For that, root and shoot biomass, nutrient uptake, mycorrhizal colonisation and nitrate reductase (NR) and phosphatase activities were analysed. Six months after planting, the shoot biomass of C. juncea was increased only by the inoculation with G. mosseae (by about 62% compared with non-mycorrhizal plants). The shoot NR and root acid phosphatase activities were increased more by inoculation with G. mosseae than with P. aurantiogriseum inoculation. The root NR activity and foliar nutrient contents were increased only by the inoculation with the AM fungus. The root Zn and Cu decreased with the AM fungus. In conclusion, the autochthonous AM fungus was an effective inoculant with regard to stimulating growth and alleviating heavy metal toxicity for plants growing on a soil contaminated by multiple heavy metals. Inoculation with an autochthonous, filamentous fungus does not seem to be a good strategy for phytoremediation of such problematic sites., This research was supported by Plan Nacional (Project AGL2006-09453-CO2-01).

El presente artículo surge de la revisión de la teoría y temas prácticos desarrollados durante el curso”Caracterización y contribución de las plantas que promueven el crecimiento de microorganismos en la sostenibilidad de la agricultura”, llevado a cabo en el Laboratorio de Microbiología de Suelos de la Corporación Colombiana de Investigación Agropecuaria (Corpoica), ubicado en Mosquera (Cundinamarca), Colombia, en julio de 2010. Esta actividad fue desarrollada en el marco de la Red Dimiagri que incluye a investigadores de Argentina, Brasil, Colombia, España, Guatemala, México y Uruguay, reunidos en una acción de coordinación financiada por el Programa Iberoamericano de Ciencia y Tecnología para el Desarrollo (Cyted). Los aspectos inherentes al crecimiento y la sanidad vegetal, el sistema radical, el suelo circundante (rizósfera), los microorganismos asociados en ese sistema y su contribución al manejo sustentable del complejo suelo-planta fueron analizados en este trabajo. También se abordan temas como la biodiversidad microbiana y su efecto en la calidad del suelo; el ciclado de nutrientes del suelo por acción microbiológica; la importancia de los microorganismos en la promoción del crecimiento vegetal y su utilización biotecnológica como alternativa para favorecer la sustentabilidad y calidad de los suelos. Además se pretende interiorizar en los conceptos relacionados con el consorcio suelo-planta-microorganismo y el objetivo de mitigar el impacto ambiental negativo causado por el uso excesivo de insumos químicos en los cultivos agrícolas, mediante la utilización de microorganismos promotores del crecimiento vegetal, que incluyen tanto a bacterias como a hongos benéficos asociados con las raíces de las plantas.

The growth of legume plants is usually enhanced by the dual symbiosis of arbuscular mycorrhizal (AM) fungi and Rhizobium bacteria. However, most reports on this topic have been carried out under optimal water regime conditions. Here, four Phaseolus vulgaris varieties were single or dual inoculated with two different AM fungus and/or two different Rhizobium strains. All plants were grown under moderate drought conditions. Surprisingly, most of the biological treatments involving one fungus and one Rhizobium together caused a deleterious effect on plant growth. However, these negative effects were dependent on the P. vulgaris variety used as well as on the symbionts implicated. The results showed that AM symbiosis inhibited nodule development and N2 fixation, causing diminution of plant growth. Therefore, under moderate drought conditions, the dual symbiosis formed by AM fungi and Rhizobium can be deleterious to P. vulgaris growth depending on the plant variety and the symbionts involved. Thus, under these common stress conditions, selection for the appropriated symbionts to each P. vulgaris variety is needed.

Aspergillus niger-treated dry olive cake (DryOC) can be used as a soil organic amendment and the aim of this work was to study the effectiveness of this amendment and a Cd-adapted arbuscular mycorrhizal (AM) fungus in improving Trifolium repens growth and nutrition in Cd-contaminated soil. In a compartmentalized growth system, consisting of a root compartment (RC) and two hyphal compartments (HCs), we investigated the influence of the amendment on intraradical and extraradical AM fungi development. In addition, we studied the viability and infectivity of the detached extraradical mycelium in plants, designated as receptor plants, grown in the HC after removal of the RC. Both the amendment and the AM fungus increased shoot and root biomass and nodulation in both the non-contaminated and Cd-contaminated soils. The positive interaction between the microbiologically treated DryOC and the AM fungus resulted in the highest plant yield, which can be explained by enhanced nutrient acquisition and arbuscular richness as well as by the immobilisation of Cd in amended soils. However, A. niger-treated DryOC had no effect on the extraradical mycorrhizal mycelium development. Although Cd decreased AM hyphal length density, symbiotic infectivity was similar in receptor plants grown in non-contaminated and contaminated soil, thus confirming the AM fungal inoculum potential. The combination of the AM fungus and A. niger-treated DryOC increased plant tolerance to Cd in terms of plant growth and nutrition and can be regarded as an important strategy for reclaiming Cd-contaminated soils., Financial support for this study was obtained from the Comision Interministerial de Ciencia y Tecnología (CICYT) PN REN 2000-1506 GLO. A. Medina is indebted to the Junta de Andalucia (Spain) and the Carl Trigger foundation (Sweden) for scholarship grants.

We investigated if the limited development of Trifolium repens growing in a heavy metal (HM) multicontaminated soil was increased by selected native microorganisms, bacteria (Bacillus cereus (Bc)), yeast (Candida parapsilosis (Cp)), or arbuscular mycorrhizal fungi (AMF), used either as single or dual inoculants. These microbial inoculants were assayed to ascertain whether the selection of HM-tolerant microorganisms can benefit plant growth and nutrient uptake and depress HM acquisition. The inoculated microorganisms, particularly in dual associations, increased plant biomass by 148% (Bc), 162%, (Cp), and 204% (AMF), concomitantly producing the highest symbiotic (AMF colonisation and nodulation) rates. The lack of AMF colonisation and nodulation in plants growing in this natural, polluted soil was compensated by adapted microbial inoculants. The metal bioaccumulation abilities of the inoculated microorganisms and particularly the microbial effect on decreasing metal concentrations in shoot biomass seem to be involved in such effects. Regarding microbial HM tolerance, the activities of antioxidant enzymes known to play an important role in cell protection by alleviating cellular oxidative damage, such as superoxide dismutase, catalase, glutathione reductase, and ascorbate peroxidase, were here considered as an index of microbial metal tolerance. Enzymatic mechanisms slightly changed in the HM-adapted B. cereus or C. parapsilosis in the presence of metals. Antioxidants seem to be directly involved in the adaptative microbial response and survival in HM-polluted sites. Microbial inoculations showed a bioremediation potential and helped plants to develop in the multicontaminated soil. Thus, they could be used as a biotechnological tool to improve plant development in HM-contaminated environments., This study was supported by “Plan Nacional I+D” Spain (Project AGL 2006-09453-CO2-02).

A mesocosm experiment was conducted to investigate the effect of the addition of Aspergillus niger-treated sugar beet waste, in the presence of rock phosphate, and inoculation with a native, metal-tolerant bacterium, Bacillus thuringiensis, on the stabilisation of soil aggregates of two mine tailings, with differing pH values, from a semiarid Mediterranean area and on the stimulation of growth of Piptatherum miliaceum. Bacterium combined with organic amendment enhanced structural stability (38% in acidic soil and 106% in neutral soil compared with their corresponding controls). Only the organic amendment increased pH, electrical conductivity, water-soluble C, water-soluble carbohydrates and plant growth, in both soils. While in neutral soil both organic amendment and bacterium increased dehydrogenase activity, only organic amendment had a significant effect in acidic soil. This study demonstrates that the use of P. miliaceum in combination with organic amendment and bacterium is a suitable tool for the stabilisation of the soil structure of degraded mine tailings, although its effectiveness is dependent on soil pH., This research was supported by the Plan Nacional (Project AGL2003-05619-CO2-01).

13 pages, 9 tables, 14 references., This study reports the effectiveness of an arbuscular mycorrhizal (AM) fungus Glomus intraradices on three clones (SOM-1, 05 and 50) of cassava (Manihot esculenta). Arbuscular mycorrhizal inoculation increased plant resistance to transplant stress from “in vitro” to “ex vitro” conditions and plant biomass (shoot and root) production was greatly enhanced by AM-colonization. The magnitude of AM growth stimulation over control clones was: 861% (SOM-1), 1042% (05) and 854% (50). Arbuscular mycorrhizal colonized cassava plants increased cassavawater uptake in terms of percentage, 62% in clone SOM-1, 24% in clone 05, and 157% in clone 50. The highest effect of AM-colonization on water content in root of clone 50 was correlated with the greatest increment in leaf tissue production (1218% over control) and with the maximum shoot/root ratio determined. The biomass distribution between shoot and root was changed by AMsymbiosis and such effect varied for each clone that may be caused by mycorrhizal changes in macro/micro-nutrients translocation/compartimentation. Cassava dependence on AM symbiosis was greatest in clone SOM-1 since AM-colonization provided the highest stem (weight, length, and diameters), leaf (weight and number), bud number, and root weight. These results lead to practical applications because AM inoculation is crucial for improving cassava yield (shoot and root) and nutrition irrespective of the clone involved. Thus, importance of AM symbiosis in micropropagated cassava clones is of great practical interest in agriculture and allows the selection of the most suitable clone for dry environments due to the particular effect on root water content that improves drought adaptation.

The plant growth, nutrient acquisition, metal translocation and antioxidant activities [ascorbate peroxidase (APX), glutatione reductase (GR), superoxide dismutase (SOD) and catalase (CAT)] were measured in plants growing in a heavy-metal (HM) multicontaminated soil inoculated with selected autochthonous microorganisms [arbuscular mycorrhizal (AM) fungus and/or plant growth promoting bacteria (PGPB)] and/or amended with an Aspergillus niger-treated agrowaste. The treated agrowaste on its own increased root growth by 296% and shoot growth by 504% compared with non-treated control plants. Both chemical and biological treatments, particularly when combined, enhanced plant shoot and root development. The stimulation effect on plant biomass was concomitant with increased AM colonization, P and K assimilation, and reduced metal translocation from soil to plant shoot. The treated residue, particularly through interactions with AM inoculation, produced the expected bioremediation effect, leading to enhanced plant development and successful rehabilitation of contaminated soil. The enhancement of CAT, APX and GR activities caused by AM inoculation suggests that AM colonization helped plants to limit oxidative damage to biomolecules in response to metal stress. The response of the plant's antioxidant activities to the amendment appears to be related to enhanced plant biomass production. The application of amendments and/or microbial inoculations to enhance plant growth and reduce metal translocation in multicontaminated soil could be a promising strategy for remediating HM pollution., This study was supported by “Plan Nacional I+D” Spain (Project AGL 2006-09453-CO2-02).

Avaliou-se o potencial de produção de ácido indol acético (AIA) in vitro por cinco isolados de fungo solubilizador de fosfato (FSF) do gênero Aspergillus sp. e quatro isolados de bactéria solubilizadora de fosfato (BSF) da família Enterobacteriaceae. Os isolados de bactéria e fungo foram incubados em meio líquido a 28ºC, por dois e quatro dias, respectivamente. Além disso, dois isolados de BSF da família Enterobacteriaceae (BSF 8 e BSF 56) foram avaliados quanto à capacidade de estimular ou inibir a germinação de esporos e o desenvolvimento micelial de duas espécies de fungos micorrízicos arbusculares (FMAs) in vitro. Foram instalados dois ensaios em placas de Petri, contendo agar-água (0,8%); um, utilizando o FMA Gigaspora margarita e o outro, com o FMA Scutellospora sp. Os tratamentos foram inoculação de BSF 8; BSF 56 e controle não-inoculado com BSF. Houve uma produção diferenciada de AIA pelos solubilizadores, destacando-se a maior produção pela maioria dos isolados fúngicos. A partir do 18º dia de incubação de Scutellospora sp., foi verificado um incremento significativo do comprimento de hifas no tratamento inoculado com BSF 8. Contrariamente, o crescimento micelial de G. margarita foi inibido pelo isolado BSF 56, a partir do 24º dia de incubação.Indolacetic acid (IAA) production was evaluated under in vitro conditions by five P-solubilizing fungi (PSF), identified as Aspergillus sp. and four P-solubilizing bacteria (PSB) of the Enterobacteriaceae family. The bacteria and fungus isolates were incubated in a liquid medium at 28ºC for two and four days, respectively. Moreover, two PSB isolates of the Enterobacteriaceae family (PSB 8 and PSB 56) were evaluated in relation to their ability to stimulate or inhibit spore germination and hyphal growth of two arbuscular mycorrhizal fungi (AMF) species under in vitro conditions. Two assays were carried out in Petri dishes with agar (0.8%), the first using the AMF Gigaspora margarita and the second with the AMF Scutellospora sp. The treatments were: inoculation of PSB 8; PSB 56 and uninoculated control. P-solubilizing isolates produced different amounts of IAA and most PSF isolates produced higher IAA than PSB. From the 18th day of incubation of Scutellospora sp., a significant increase in hyphal growth in the treatment inoculated with PSB 8 was observed. In contrast, PSB 56 inhibited the hyphal growth of Gigaspora margarita from the 24th day of incubation.

Coinoculation with plant growth–promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungi (AMF) has been proposed as an efficient method to increase plant growth. In this article we investigate how the interaction between three different AMF isolates (Glomus constrictum autochthonous, GcA; G. constrictum from collection, GcC; and commercial Glomus intraradices, Gi) and a Bacillus megaterium strain isolated from a Mediterranean calcareous soil affects Lactuca sativa L. plant growth. Inoculation with B. megaterium increased plant growth when in combination with two of the AMF isolates (GcA and Gi), but decreased it when in combination with GcC. At the same time, plants inoculated with the GcC fungus alone or in combination with B. megaterium (GcC+Bm) showed leaf symptoms of stress injury by accumulating proline and reducing the amount of photosynthetic pigments, whereas the opposite occurred in plants coinoculated with Gi fungus and B. megaterium (Gi+Bm). GcC+Bm leaves also presented the highest glucose-6-phosphate dehydrogenase (G6PDH) and the lowest glutamine synthetase (GS) enzymatic activities, whereas Gi+Bm leaves showed the highest GS activity. Results on these enzymatic activities are further discussed in relation to plant growth and performance., R. Aroca was supported by Juan de la Cierva Program (Ministerio de Educación y Ciencia).

This study investigated how two different N sources used as fertilizer (NO3− or NH4+) interact with an inoculated arbuscular mycorrhizal (AM) fungus (Glomus etunicatum) in an Andisol from southern Chile. The effect of NO3− or NH4+ on mycorrhizal and non-mycorrhizal wheat plants was measured on key root–soil interface activities: pH, acid phosphatase (P-ase) activity and P availability. Root AM colonization, extraradical mycelium length and spore number were also examined at three stages of AM symbiosis development (120, 150 and 240 days after sowing, DAS). The effect of N-source on AM propagule formation was used as an index of the quality and vigor of AM colonization. Mycorrhizal root length was greater with NO3− than with NH4+ at all times. The NO3− source also improved extraradical mycelium density, which reached its maximum at 150 DAS. At each harvest the spore number in the rhizosphere soil was also greater with NO3− fertilization. This NO3− effect on spore formation ranged from 20% at a 120 DAS to 287% at a 240 DAS increase, compared with NH4+. Extraradical mycelium and AM efficiency for P acquisition appeared to be related. The particular fungus/plant metabolism as affected by N sources (NO3− or NH4+) applied did not result in differential plant growth or in changes in N plant acquisition, but affected AM development and activity. Differences in soil pH, available P or P-ase activity in soil seems not to be responsible for the improved physiological status of mycorrhizal development in NO3− fed plants. Mycorrhizal propagule formation in this soil and the high persistence of extraradical mycelium are important factors which may have a strong influence on the next crop, and thus, this aspects should be considered when a cropping system is designed. The influence of N sources on AM performance is of ecological and practical interest in volcanic soils when conventional management is used., This work was supported by Fondecyt, grant 1990756, from Comision Nacional Cientifica y Tecnologica, Chile. The authors also acknowledge financial support given to R. Azcon for travel and expenses while staying in Chile through Andes Foundation project C-13755-28.

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., A Marie Curie Fellowship of the European Commission for Almudena Medina supported this work.

In a biopurification system such as a biobed, the rhizosphere of the grass layer may be a significant factor for promoting pesticide dissipation in the biomixture. The rhizosphere effect of a Lolium perenne, Festuca arundinacea and Trifolium repens mixture on the dissipation of a pesticide combination that was composed of atrazine, chlorpyrifos and isoproturon was studied. The assay was performed using glass pots divided into two separate compartments (root surface and root-free), each filled with an organic biomixture (oat husk, top soil and peat) and contaminated with the pesticide mixture at 5 mg kg-1.Non-planted and non-contaminated pots were also used as controls. The results indicated that there were high atrazine, chlorpyrifos and isoproturon dissipation in the planted pots compared with the unplanted pots. An inverse correlation was found throughout the assay between phenoloxidase activity and residual pesticide (r =0.684 to 0.952). Indeed, fungal biomass was positively correlated with phenoloxidase activity on day 1 (r =0.825) and day 30 (r =0.855). Besides, exudation of oxalic and malic acid in contaminated pots was higher than in the control without pesticides, associated with oxidation of the pesticide mixture in the biomixture of a bioded system. Therefore, the grass layer enhances pesticide removal in biobeds., This work was supported by FONDECYT project Nº 1120963, CONICYT/FONDAP/15130015, CONICYT-21110405-2011 doctoral support scholarship, CONICYT-24121122 thesis support scholarship, BECAS CHILE–75120104-2012 doctoral internship and by the Spanish Science and Innovation Ministry and co-financed with European funds through the project (CTM2010-16807).

A field experiment was carried out to assess the effectiveness of combining mycorrhizal inoculation with a native AM fungus (Glomus sp.) and the addition of an urban organic waste compost (OWC) applied at two rates (0.5 and 2.0% (w:w)), with regard to promoting the establishment of Anthyllis cytisoides L. seedlings in a heavy metal polluted mine tailing, as well as stimulating soil microbial functions. The results showed that the combined use of the highest dose of OWC and AM inoculation significantly increased shoot biomass – by 64% – compared to the control value. However, the separate use of each treatment had no effect on the shoot biomass of this shrub species. At the 2% rate, OWC enhanced root colonisation by the introduced fungus as well as soil nutrient content and soil dehydrogenase and ß-glucosidase activities. The combined treatment increased the uptake of Zn and Mn in shoots, although only Zn reached excessive or potentially toxic levels. This study demonstrates that the combination of organic amendment and an AM fungus is a suitable tool for the phytomanagement of degraded mine tailings, although its effectiveness is dependent on the dose of the amendment., This research was supported by Plan Nacional (Project AGL2012-39057-CO2-01).

Autochthonous microorganisms [a consortium of arbuscular-mycorrhizal (AM) fungi and Bacillus thuringiensis (Bt)] were assayed and compared to Rhizophagus intraradices (Ri), Bacillus megaterium (Bm) or Pseudomonas putida (Psp) and non-inoculation on Trifolium repens in a natural arid soil under drought conditions. The autochthonous bacteria Bt and the allochthonous bacteria Psp increased nutrients and the relative water content and decreased stomatal conductance, electrolyte leakage, proline and APX activity, indicating their abilities to alleviate the drought stress. Mycorrhizal inoculation significantly enhanced plant growth, nutrient uptake and the relative water content, particularly when associated with specific bacteria minimizing drought stress-imposed effects. Specific combinations of autochthonous or allochthonous inoculants also contributed to plant drought tolerance by changing proline and antioxidative activities. However, non-inoculated plants had low relative water and nutrients contents, shoot proline accumulation and glutathione reductase activity, but the highest superoxide dismutase activity, stomatal conductance and electrolyte leakage. Microbial activities irrespective of the microbial origin seem to be coordinately functioning in the plant as an adaptive response to modulated water stress tolerance and minimizing the stress damage. The autochthonous AM fungi with Bt or Psp and those allochthonous Ri with Bm or Psp inoculants increased water stress alleviation. The autochthonous Bt showed the greatest ability to survive under high osmotic stress compared to the allochthonous strains, but when single inoculated or associated with Ri or AM fungi were similarly efficient in terms of physiological and nutritional status and in increasing plant drought tolerance, attenuating and compensating for the detrimental effect of water limitation., This study was supported by “Plan Nacional I+D” Spain (project AGL-2009-12530).

Three bacterial autochthonous strains, namely Enterobacter sp.; Bacillus thuringiensis and Bacillus sp. were isolated from the rhizosphere of Mediterranean shrub species growing in a semiarid environment and analyzed alongside with the allochthonous Bacillus megaterium, used as reference drought tolerant strain, for their drought tolerance and plant growth promoting rhizobacteria (PGPR) capacities. The preliminary studies, done in axenic culture under non-stress and stress conditions show that Enterobacter sp. resulted in the most tolerant bacteria to osmotic stress factors. In contrast, Bacillus sp. was the most sensitive bacteria to osmotic stress factors and concomitantly, under these conditions, produced the highest amounts of ACC deaminase, poly-β-hydroxybutyrate and proline, to compensate its lack of stress tolerance. The PGPR activities of the tested bacterial strains under non-osmotic and osmotic stress conditions were determined by evaluating hormone (SA, ABA, JA and IAA) and ACC-deaminase production and phosphate solubilization. To analyze the bacterial efficiency as inoculants four shrubs species (Thymus vulgaris, Santolina chamaecyparissus, Lavandula dentata and Salvia officinalis), adapted to aridity, were selected. All the tested bacteria improved nutrition and physiological variables related to drought tolerance of the test plant. In addition, in S. chamaecyparissus and S. officinalis also increased mycorrhizal colonization. The application of fermented agrowaste resulted in effectively improving nutrient uptake and also interacted positively with most of the bacteria increasing plant nutrients content and drought tolerance but their effectiveness depended on the plant species and bacteria involved. In fact, in B. megaterium and the fermented agrowaste increased P and K uptake in S. chamaecyparissus (by 109% P and by 66% K), in L. dentata (by 75% P and 33% K) and in S. officinalis (by 63% P and 52% K). However, without amendment, the native B. thuringiensis was the most efficient strain in increasing P content in T. vulgaris (by 51%) and in S. chamaecyparissus (by 11%), and K content in L. dentata (by 63%), which decreased the stomatal conductance. Results show that under axenic conditions the stress applied did not suppress the PGPR abilities of assayed bacteria which indicated their potential to be tested as inoculants under detrimental conditions. The applied treatments resulted fundamental for these shrubs to reach their optimal nutritional and physiological traits suggesting their possible applicability under the natural semiarid drought conditions. The multiplicity and complexity of bacterial activities and the intrinsic characteristics of plant reactions to drought could explain the unpredictable results obtained by using these bacteria as plant inoculants. These and other factors are controlling the PGPR effects therefore it made difficult to generalize and to explain the cause/effect of the variable responses to be obtained. The results suggest the potentiality of the target bacteria and fermented agrowaste to be used as a biotechnological tool to help plants and reforestation in semiarid lands., E. Armada was financed by Ministry of Science and Innovation (Spain). This work was carried out in the framework of the project reference AGL2009-12530-C02-02.

The growth of clover (Trifolium repens ) and its uptake of N, P and Ni were studied following inoculation of soil with Rhizobium trifolii, and combinations of two Ni-adapted indigenous bacterial isolates (one of them was Brevibacillus brevis) and an arbuscular mycorrhizal (AM) fungus (Glomus mosseae). Plant growth was measured in a pot experiment containing soil spiked with 30 (Ni I), 90 (Ni II) or 270 (Ni III) mg kg−1 Ni-sulphate (corresponding to 11.7, 27.6 and 65.8 mg kg−1 available Ni on a dry soil basis). Single inoculation with the most Ni-tolerant bacterial isolate (Brevibacillus brevis) was particularly effective in increasing shoot and root biomass at the three levels of Ni contamination in comparison with the other indigenous bacterial inoculated or control plants. Single colonisation of G. mosseae enhanced by 3 fold (Ni I), by 2.4 fold (Ni II) and by 2.2 fold (Ni III) T. repens dry weight and P-content of the shoots increased by 9.8 fold (Ni I), by 9.9 fold (Ni II) and by 5.1 fold (Ni III) concomitantly with a reduction in Ni concentration in the shoot compared with non-treated plants. Coinoculation of G. mosseae and the Ni-tolerant bacterial strain (B. brevis) achieved the highest plant dry biomass (shoot and root) and N and P content and the lowest Ni shoot concentration. Dual inoculation with the most Ni-tolerant autochthonous microorganisms (B. brevis and G. mosseae) increased shoot and root plant biomass and subtantially reduced the specific absorption rate (defined as the amount of metal absorbed per unit of root biomass) for nickel in comparison with plants grown in soil inoculated only with G. mosseae. B. brevis increased nodule number that was highly depressed in Ni I added soil or supressed in Ni II and Ni III supplemented soil. These results suggest that selected bacterial inoculation improved the mycorrhizal benefit in nutrients uptake and in decreasing Ni toxicity. Inoculation of adapted beneficial microorganisms (as autochthonous B. brevis and G. mosseae) may be used as a tool to enhance plant performance in soil contaminated with Ni., A. Vivas wants to thank the Fundación Gran Mariscal de Ayacucho (Venezuela) for the scholarship. The project was further supported by the CSIC-HAS bilateral agreement, the Hung. National Research Fund (OTKA T046610) and the COST Action 8.38 and the EU-fp 5 QLK (Mycorem) program, which are highly acknowledged.

9 pages, 2 figures, 4 tables., The effects of mycorrhizal inoculation, with an arbuscular mycorrhizal (AM) fungus (Glomus intraradices Schenck and Smith) or with a mixture of three AM fungi (G. intraradices, G. deserticola (Trappe, Bloss. and Menge) and G. mosseae (Nicol and Gerd.) Gerd. and Trappe), and addition of composted sewage sludge or Aspergillus niger-treated dry olive cake (DOC) residue on aggregate stabilisation of the rhizosphere soil of Juniperus oxycedrus were studied. The influence of such structural improvements on the establishment of J. oxycedrus was evaluated. Six months after planting, the inoculation with the mixture of three AM fungi and the combination of G. intraradices with both organic amendments had significantly enhanced the structural stability. Water soluble C and carbohydrates values were increased only with the addition of composted sewage sludge or fermented DOC. The addition of both organic amendments, particularly fermented DOC, decreased significantly the dehydrogenase, urease, protease and β-glucosidase activities. Rhizosphere soil from the inoculation treatments had higher dehydrogenase and β-glucosidase activities than control soil. Both the organic amendments addition and the mycorrhizal inoculation treatments increased significantly shoot biomass in J. oxycedrus. AM inoculation treatments were more effective with respect to increasing shoot biomass than the addition of organic amendments alone, and there were no significant differences between the two mycorrhization treatments (on average, about 53% higher with respect to control plants and about 18% higher with respect to plants grown in the amended soil)., This research was supported by the Seneca Foundation (Project PI-69/00815/FS/01) and by CICYT (Project AGL2003-05619-CO2-01).

[Aims]: This study investigates how autochthonous micro-organisms [bacterium and/or arbuscular mycorrhizal (AM) fungi] affected plant tolerance to Zn contamination., [Methods and Results]: Zinc-adapted and -nonadapted Glomus mosseae strains protected the host plant against the detrimental effect of Zn (600 μg g−1). Zn-adapted bacteria increased root growth and N, P nutrition in plants colonized by adapted G. mosseae and decreased the specific absorption rate (SAR) of Cd, Cu, Mo or Fe in plants colonized by Zn-nonadapted G. mosseae. Symbiotic structures (nodule number and extraradical mycelium) were best developed in plants colonized by those Zn-adapted isolates that were the most effective in increasing plant Zn tolerance. The bacterium also increased the quantity and quality (metabolic characteristics) of mycorrhizal colonization, with the highest improvement for arbuscular vitality and activity. Inocula also enhanced soil enzymatic activities (dehydrogenase, β-glucosidase and phosphatase) and indol acetic acid (IAA) accumulation, particularly in the rhizosphere of plants inoculated with Zn-adapted isolates., [Conclusions]: Glomus mosseae strains have a different inherent potential for improving plant growth and nutrition in Zn-contaminated soil. The bacterium increased the potential of mycorrhizal mycelium as inoculum., [Significance and Impact of the Study]: Mycorrhizal performance, particularly that of the autochthonous strain, was increased by the bacterium and both contributed to better plant growth and establishment in Zn-contaminated soils., A. Vivas wishes to thank the Fundación Gran Mariscal de Ayacucho (Venezuela) for the scholarship. To the project CSIC-Hungarian Academy of Science (1997–1999) on ‘The role of endomycorrhizal fungi in counter-balancing various environmental stresses.

Although the discovery of aquaporins in plants has resulted in a paradigm shift in the understanding of plant water relations, the relationship between aquaporins and plant responses to drought still remains elusive. Moreover, the contribution of aquaporin genes to the enhanced tolerance to drought in arbuscular mycorrhisal (AM) plants has never been investigated. Therefore, we studied, at a molecular level, whether the expression of aquaporin-encoding genes in roots is altered by the AM symbiosis as a mechanism to enhance host plant tolerance to water deficit. In this study, genes encoding plasma membrane aquaporins (PIPs) from soybean and lettuce were cloned and their expression pattern studied in AM and nonAM plants cultivated under well-watered or drought stressed conditions. Results showed that AM plants responded to drought stress by down-regulating the expression of the PIP genes studied and anticipating its down-regulation as compared to nonAM plants. The possible physiological implications of this down-regulation of PIP genes as a mechanism to decrease membrane water permeability and to allow cellular water conservation is further discussed., This work and R. Porcel were financed by CICYT-FEDER (Project AGL2002–03952).

In this study, we have determined whether the arbuscular mycorrhizal (AM) symbiosis is able to alter the pattern of Δ1-pyrroline-5-carboxylate synthetase (p5cs) gene expression under drought stress and whether such possible alteration functions in the protection of the host plants against drought. To achieve this, we cloned a P5CS-encoding gene from Glycine max (gmp5cs) and another from Lactuca sativa (lsp5cs) and analyzed their contribution to the response against drought in control and AM soybean and lettuce plants. The analysis of gmp5cs and lsp5cs gene expression showed that these genes were up-regulated by drought stress. The highest gene expression was found in non-inoculated plants subjected to drought. A contrasting result was obtained in soybean plants singly inoculated with Bradyrhizobium japonicum, where the gmp5cs gene showed little up-regulation in roots under drought stressed conditions. Moreover, both soybean and lettuce AM plants showed lower p5cs transcript accumulation under drought stress than non-inoculated plants. The present results indicate that the induction of p5cs gene is not a mechanism by which the AM symbiosis protects their host plant against drought., This work and R. Porcel were financed by CICYT-FEDER (Project AGL2002-03952).

12 pages, 1 figure, 7 tables., 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)., This research was supported by the EC + CICYT co-financed FEDER programme (REN 2000-1724- CO3-01).