In the original publication [...].

Ensuring food security in a framework of environmental sustainability is the greatest challenge of the 21st century. The rapid population growth together with changing consumption patterns associated with new lifestyles mean that total demand for food is increasing at a faster pace than that of the production capacity. To overcome this challenge we need to transform agriculture into a more efficient and less polluting activity. This may be achieved through harnessing the trillions of organisms inhabiting the soil. In this work we show how the use of microbial consortia can contribute to increased productivity and efficient use of nutrients in a maize field. The combined use of arbuscular mycorrhizal fungi and bacteria that promote plant growth, when applied in a field experiment were able to compensate for the reduction in fertilizer by 33%. The results show that the application of the microbial consortium increased nitrogen fixing and phosphorus solubilising bacteria in the soil, which may explain the increased uptake of these nutrients by the plants.

Iron (Fe) chlorosis is very common in plants cultivated in calcareous soils of the Mediterranean basin and is usually corrected by the application of Fe chelates to the soil, which can have a negative impact on the environment. The aim of this experiment was to assess the role of quercetin, a natural compound widely present in plants and known to bind Fe, in correcting Fe chlorosis when supplied in the Hoagland nutrient solution. In this context, strawberry plants were grown at different Fe concentrations, with 0 (Fe0), 1 (Fe1) and 5 (Fe5) mu M of Fe in the nutrient solution, until the onset of clear Fe chlorosis symptoms. Subsequently, the recovery of Fe chlorosis was investigated through the addition of Fe and/or quercetin (Q) to nutrient solutions. Throughout the experiment, leaf chlorophyll (Chl) was estimated using the SPAD values. The root ferric chelate-reductase (FCR) activity was determined in the root apices, and the foliar Fe concentration was also quantified. At the end of the experiment, plants grown without Fe but supplemented with Fe1 plus quercetin [Fe0+(Fe1+Q)] recovered completely from Fe chlorosis and showed a Chl concentration (700-800 mu mol m( 2)) in young leaves similar to that observed in control plants (Fe5). The remaining treatments exhibited lower Chl concentrations, with values ranging from 92.4 to 217.0 mu mol of Chl per m(2). FCR activity was approximately five-to six-fold higher in the Fe0+(Fe1+Q) treatment than in the Fe0 and Fe5 treatments. However, the plants that were consistently grown with Fe in the nutrient solution (Fe1 and Fe5) exhibited the highest Fe content in their leaves. The findings suggest that quercetin has the potential to function as an Fe complexing agent, thereby enhancing the recovery of strawberry plants with Fe deficiency.

BackgroundIron chlorosis is an abiotic stress of worldwide importance affecting several agronomic crops. It is important to understand how plants maintain nutrient homeostasis under Fe deficiency and recovery. AimsWe used the virus-induced gene silencing (VIGS) method to elucidate the role of the FRO1 gene in tomato plants and identify the impact on regulation of the root ferric-chelate reductase (FCR) activity and nutritional homeostasis. MethodsTomato plantlets cv. "Cherry" were transferred into half-strength Hoagland's nutrient solution containing 0.5 & mu;M of Fe (Fe0.5). In phase I, two treatments were established: control (Fe0.5) plants and VIGS-0.5 plants corresponding to plants with the FRO1 gene silenced. In phase II, plants from Fe0.5 and VIGS-0.5 were transferred to new nutrient solution and then grown for a further 14 days under 0 and 10 & mu;M of Fe (as 0.5 & mu;M would not be enough for the larger plants during phase II). Therefore, four treatments were imposed: Fe0, Fe10, VIGS-0, and VIGS-10. ResultsVIGS-0.5 plants had significantly lower chlorophyll (Chl) and root FCR activity compared to the respective non-silenced plants and retained more Cu and Zn in the roots at the expense of stems (Cu) or young leaves (Zn). Iron concentration in roots and stems decreased in FRO1 gene-silenced plants, compared to control plants, but the allocation to different organs was similar in both treatments. ConclusionsThere was a partial recovery of leaf Chl in the VIGS-10 plants and a higher concentration of Fe in all organs. In contrast, the allocation of Cu to roots decreased in the VIGS-10 plants.

Iron is an essential micronutrient for citrus, playing an important role in photosynthesis and yield. The aim of this paper was to evaluate the tolerance to Fe deficiency of five citrus rootstocks: sour orange (S), Carrizo citrange (C), Citrus macrophylla (M), Troyer citrange (T), and Volkamer lemon (V). Plants were grown for 5 weeks in nutrient solution that contained the following Fe concentrations (in µM): 0, 5, 10, 15, and 20. At the end of the experiment, biomass (dry weight—DW), leaf area, total leaf chlorophyll (CHL), and the activity of root chelate reductase (FCR) were recorded. Additionally, the mineral composition of roots (R) and shoots (S) was evaluated. Principal component analysis was used to study the relationships between all parameters and, subsequently, the relations between rootstocks. In the first component, N-S, P-S, Ca-S, Cu-S, Zn-S, Mn-S, Zn-R, and Mn-R concentrations were related to leaf CHL and FCR. Increases in leaf CHL, Mg-R, and DW (shoots and roots) were inversely related to Cu-R, which was shown in the second component. The values obtained were consistent for V10, C15, and C20, but in contrast for S0 and S5. In conclusion, micronutrient homeostasis in roots and shoots of all rootstocks were affected by Fe stress conditions. The Fe/Cu ratio was significantly related to CHL, which may be used to assist rootstock performance.

The large economic costs and environmental impacts of iron-chelate treatments has led to the search for alternative methods and compounds to control iron (Fe) deficiency chlorosis. Strawberry plants (Fragaria x ananassa) were grown in Hoagland's nutrient solution in a greenhouse with two levels of Fe: 0 and 10 μM Fe(III)-EDDHA. After 20 days, plants growing without Fe showed typical symptoms of Fe deficiency chlorosis in young leaves. Then, the adaxial and abaxial sides of one mature or one young leaf in each plant were brushed with 10 mM malic (MA), citric (CA) or succinic (SA) acids. Eight applications were done over a two-week period. At the end of the experiment, the newly emerged (therefore untreated), young and mature leaves were sampled for nutritional and metabolomic analysis, to assess the effectiveness of treatments. Leaf regreening was monitored using a SPAD-502 apparatus, and the activity of the ferric chelate-reductase activity (FCR) was measured using root tips. Iron deficiency negatively affected biomass and leaf chlorophyll but did not increase FCR activity. Application of succinic acid alleviated the decrease in chlorophyll observed in other treatments, and the overall nutritional balance in the plant was also changed. The concentrations of two quinic acid derivatives increased under Fe deficiency and decreased in plants treated with succinic acid, and thus they are proposed as Fe stress markers. Data suggest that foliage treatments with carboxylates may be, in some cases, environmentally friendly alternatives to Fe(III)-chelates. The importance of Fe mobilization pathways in the formulation of new fertilizers is also discussed.

The traditional agricultural production systems are evolving more toward organic, sustainable or environmental friendly systems and products; however, it is important to keep the yield and the quality of crops. The aim of this work was to evaluate the recovery of iron deficient strawberry plants by foliar spray, using a gramineous plants extract (GE). Bare-root transplants of strawberry (Fragaria x ananassa Duch. cv "Diamond") were grown in a Hoagland's nutrient solution with iron (Fe10) or without (Fe0). Forty-two days after Fe deprivation, plants grown without iron became chlorotic and GE was applied. Three foliar applications were done, once per week and the regreening was monitored using a SPAD apparatus. After two applications, a rapid but transient regreening was detected in young leaves. Nevertheless, biomass and root/shoot ratio of recovered plants (GE treatment) were similar to chlorotic plants (Fe0 treatment). Phosphorous, Mn and Fe contents were higher in crowns of GE plants at the end of the experiment (67 days). The concentration of organic acids and ferric chelate-reductase (FC-R) activity was also significantly higher in GE treatment. It is possible that the high chelating capacity of the extract was responsible for the Fe internal transport and use.

Readers should note that there was an error in this article as originally published.

Fly ash (FA) from biomass combustion and biological sludge (S), both wastes from the pulp and paper industry, were granulated in different proportions (90% FA+10% S, and 70% FA+30% S w/w, dry weight basis, dw) and used to recover the functionality of soils affected by mining activities (Aljustrel, Iberian Pyrite Belt), with and without the application of municipal solid waste compost (MSWC). Application doses of both mixtures were 2.5, 5.0 and 10% (w/w, dw). These materials corrected soil acidity to circumneutral values and increased extractable P and K concentrations. A significant increase in soil organic matter (from 0.6 to 0.8–1.5% w/w, dw) and N content (from 0.04 to 0.09–0.12% w/w, dw) was also observed, but only when MSWC was applied. The soil was already heavily contaminated with Cu, Pb and Zn and the application of amendments did not increase their pseudo-total concentrations. The CaCl2 extractable fractions of both Cu and Zn decreased to very low values. The improvement in soil quality, compared to fertilizer only treatment, was further evidenced by the increase in some soil enzymatic activities (dehydrogenase, β-glucosidase and cellulase), with a better response for the granules with the higher proportion of biological sludge, as well as by the decrease in the soil-water extract toxicity towards different organisms (Daphnia magna, Thamnocephalus platyurus, and Pseudokirchneriella subcapitata). Agrostis tenuis germinated and grew during the first month only in the amended pots, but, after that, a considerable phytotoxic effect was evident. This was mainly attributed to salt stress or to some specific ionic toxicity. In conclusion, to establish a long-term plant cover in mining soils amended with biomass ash-based materials, the selection of plants with higher resistance to salinity and/or the stabilization of the amendments, to reduce their soluble salt content, is recommended.

Several of the plant species grown in calcareous soils in arid and semi-arid regions are iron-deficient, a condition known as iron chlorosis. Strawberry shows a wide genotypic variation in tolerance to iron deficiency and foliar sprays can be a cheap and environmental-friendly alternative to soil treatments to control iron chlorosis. The aim of the present study was to evaluate the effect of different iron compounds applied to leaves on growth of strawberry (Fragaria x ananassa Duch. 'Splendor'). Plants were grown in polyethylene bags (100x30x12 cm) filled with coconut peat in a greenhouse under natural light and temperature. A completely randomized block design (4 treatments x 3 replicates) was used in a hydroponic system. Each replicate consisted of 10 plants. The treatments were iron sulphate (IS; 2 mM), IS plus citric acid (CA; 2+10 mM), grass clipping extract (GE; Patent PT/103584/2009) and distilled water as a control. A non-ionic wetting agent was used in all treatments (Etaldyne, Rhone-Poulenc, 0.5 mL L-1). Treatments were applied with a manually operated sprayer by fully wetting the plants until the product dripped from the foliage. Treatments started on April 30, when the crown diameter was approximately 249 mm, and were made every week until May 20, when the crop was harvested. The treatments were applied a total of four times. A total volume of 1.5 L was used to spray all the 30 plants treated. The crown diameter and soil-plant analysis development (SPAD) values were measured. The main effects of treatments on vegetative parameters were evaluated.

Au cours d’une séance d’hémodialyse (HD), il est considéré que seulement 25 à 40 % du phosphate inorganique (Pi) épuré provient du compartiment extra-cellulaire. Des données suggèrent que les 60 à 75 % restants pourraient provenir du compartiment intracellulaire. En utilisant la spectroscopie par résonance magnétique du phosphore 31 (31P-MRS), une augmentation de la concentration intracellulaire en Pi durant l’HD chez le porc a été observée dans un modèle d’insuffisance rénale aiguë. Ce résultat conforte l’hypothèse d’une origine intracellulaire du phosphate épuré, sans qu’une origine osseuse n’ait pu complètement être écartée. Le but de notre étude est de vérifier si le Pi intracellulaire augmente au cours d’une séance d’hémodialyse chez les patients insuffisants rénaux chroniques terminaux (IRCT) en hémodialyse chronique depuis plus de 6 mois. Onze patients IRCT ont été inclus dans cette étude monocentrique, prospective, interventionnelle où les concentrations intracellulaires en Pi et en ATP ont été mesurées par 31P-MRS pendant une séance d’HD standard de 4 heures. Le bilan phosphocalcique, la PTH (début et fin de dialyse) et la balance calcique ont également été dosé. Pendant l’HD, la phosphatémie chute rapidement au cours de la première heure (−41 %, p < 0,001) puis baisse lentement jusqu’à la fin de la séance alors que l’épuration du phosphate est presque constante au cours du temps (38 mmol au total en moyenne). La concentration intracellulaire en Pi suit une évolution en 2 phases durant l’HD : durant la première heure, la concentration intracellulaire en Pi reste stable (p = 0,9) avant de diminuer jusqu’à la fin de la séance (p = 0,001). De même, la concentration intracellulaire en βATP suit une évolution en 2 phases durant l’HD : durant la première heure, la concentration intracellulaire en βATP décroît (−17 %, p = 0,038) avant de se stabiliser jusqu’à la fin de la séance (p = 0,46). La calcémie augmente (de 2,2 à 2,5 mmol/L, p < 0,01), et la PTH baisse entre le début et la fin de la séance (163,9 et 93,6 pg/mL respectivement). La balance calcique est positive (+17,1 mmol au total). Au vu des résultats de la balance calcique, il apparaît peu probable que le compartiment osseux participe à une libération de phosphate dans le plasma durant l’HD. Cette étude confirme pour la première fois une origine intracellulaire du phosphate épuré pendant l’HD chez des patients IRCT.

In order to aggregate value to the grape stem (wastes), this research aim was to increase the adsorption capacity of Cd2+ by chemical modifications on grape stems. The grape stems were milled and sieved, resulting in the biosorbent, which was used for the chemical modifications resulting in E. H2O2, E. H2SO4 and E. NaOH. These were characterized by such means as its pH(pzc), Fourier transform-infrared (FTIR) spectroscopy, porosimetry, thermal stability and scanning electron microscopy. The ideal adsorption dose, the pH influence on adsorption, kinetics, equilibrium and thermodynamics studies were carried out. The FTIR spectroscopy suggests the occurrence of carboxyl, amine, and phenolic acting in Cd2+ sorption. The modification on grape biomass caused small increase in pore volume and specific surface area. The grape-based adsorbents have similar thermal stability, with irregular appearance and heterogeneity. 5.0 g kg(-1) is the best adsorption dose. The modified adsorbents exhibited increase in Cd2+ removal of 66% for E. NaOH, 33% for E. H2O2 and 8.3% for E. H2SO4. The use of grape stem as adsorbent is an attractive alternative, because its wastes have great availability, low cost and great potential for metal adsorption processes.

Current research produced modified adsorbents from pinus bark with high removal capacity of Cd(II), Pb(II) and Cr(III) from water. Pinus barks were obtained directly from pinus logs and its biomass was chemically modified by solutions of H2O2, H2SO4 and NaOH 0.1 mol L-1. The adsorbents were characterized by means of their chemical composition, their point of zero charge (pH(pzc)), FT-IR, SEM, porosity and superficial area. Experiments evaluated the effect of contact time and equilibrium. Best results showed an increase in adsorption capacity for Cd, Pb and Cr of 413 (Q(m) of Langmuir), 259 (Q, of Langmuir) and 207% (Kf of Freundlich) for P. NaOH, P. NaOH and P. H2SO4, respectively. The modifying solutions were effective, and chemically modified the pinus bark, increasing the removal quantity of metals from water.

The aim of this study was to evaluate the use of drinking-water treatment residuals (DWTR) in the amendment of a soil affected by mining activities (Aljustrel mine, Portuguese sector of the Iberian Pyrite Belt), considering the effects on its chemical, biochemical and ecotoxicological characteristics. The DWTR had neutral characteristics (pH 6.7) and an organic matter (OM) content of 575 g kg(-1) dry matter (DM), which makes them a potential amendment for the remediation of mine degraded soils, as they may correct soil acidity and reduce the extractable metal fraction. An incubation assay, with soil and DWTR, with or without lime, was carried out to test the doses to be used in the assisted-phytostabilization experiment. Based on the results obtained, the doses of DWTR used were the equivalent to 48, 96, and 144 t DM ha(-1), with and without lime application (CaCO3 11 t DM ha(-1)). Agrostis tenuis Sibth was used as the test plant. Some amendments doses were able to improve soil characteristics (pH and OM content), to decrease metal extractability by 0.01 M CaC1(2) (especially for Cu and Zn), and to allow plant growth, that did not occur in the non-amended soil. Copper, Pb and Zn concentrations in the plant material were lower than the maximum tolerable level for cattle feed, used as an indicator of risk of entry of those metals into the human food chain. The simultaneous application of DWTR (96 and 144 t ha(-1)), with lime, allowed a reduction in the mine soil ecotoxicity, as evaluated by some lethal and sub-lethal bioassays, including luminescence inhibition of Vibrio fischeri, Daphnia magna acute immobilization test, mortality of Thamnocephalus platyurus, and 72-h growth inhibition of the green microalgae Pseudokirchneriella subcapitata. However, DWTR were unable to increase soil microbial activity, evaluated by dehydrogenase activity, an important soil-health indicator. Also, OM content and N-kjeidahl, concentrations increased slightly but remained low or very low (P and K extractable concentrations were not affected). In general, the bioassays highlighted a decrease in soil ecotoxicity with the presence of lime and DWTR (144 t DM ha(-1)). In conclusion, DWTR are recommended to amend acidic soils, with high concentrations of trace elements, but an additional application of organic or mineral fertilizers should be considered.

The aim of this work was to understand how two different soil types (calcareous - C and non-calcareous soils - NC) affect carob tree nutritional performance and bioactive compounds present in the pulp of the pod. Two orchards were selected in two separately separate locations: in soil C, trees were grown under calcareous conditions, with high percentage of active lime (>9%) and a soil pH of 8.1 and in soil NC, no carbonates were present and soil pH was 6.6. Leaf mineral composition, total leaf chlorophyll and several bioactive compounds were monitored in trees of the cv. 'Mulata' during three years and covering two seasons in both orchards. Unripe and ripe pods were separately analyzed. Trees in the NC site were smaller and less vigorous but presented higher leaf chlorophyll, and higher N, Mg, Zn, Fe and Mn in leaves, than trees of the C site. In the latter, only Ca and K were slightly higher. Unripe pods in both orchards showed significantly higher polyphenols content and high anti-oxidant activity (expressed as DPPH). Condensed tannins content was related to leaf mineral composition (N, Zn and Mn) but among these, Mn was the most important and its accumulation in leaves is a good indicator of anti-oxidant activity. Condensed tannins content was higher in unripe pods of trees in the NC site.

Arbuscular mycorrhizal fungi (AMF) are promoted as biofertilizers for cleaner agricultural production. So far, most researchers have investigated the effects of AMF on plant growth under highly controlled conditions with sterilized soil. However, how the soil microbial community shapes AMF's impact on host plant performance is still poorly documented. To focus on the impact of belowground interactions (plant-AMF-soil microbes) alone, we compared sterilized versus non-sterilized soil, inoculating maize (Zea mays ssp. mays) seedlings with five commercial AMF inoculants (Claroideoglomus claroideum, Funneliformis mosseae, Gigaspora sp., Rhizophagus irregularis and Scutellospora sp.). Plants were pot-cultivated for nine weeks using soil which had been used for maize monocropping in the field. AMF inoculation was successful, despite an abundant native AMF community. As hypothesized: i) the soil microbial community interfered with AMF's benefits for maize growth; ii) these benefits depended on the AMF species, as C. claroideum, F. mosseae and Gigaspora sp. overruled the soil's legacy from maize monocropping. When plants were grown in sterilized soil, we found little to no effects of AMF inoculation on maize growth and nutrients acquisition. AMF's benefits to the host plants could not be explained by improved nutrition alone, since interaction with the remainder soil microbes also differed between inoculated AMF. Data show that the soil microbial community and AMF species should be taken into consideration when applying AMF inoculants in agriculture.

Iron (Fe) deficiency is a nutritional disorder in plants. Poncirus trifoliata is susceptible to Fe deficiency, but symptoms of Fe deficiency are rare in Ceratonia siliqua, a slow-growing species. Specimens of the two species were grown in nutrient solutions containing three Fe concentrations: without Fe (0 mu M), 1 mu M Fe, and either 10 mu M Fe (for Ceratonia) or 40 mu M Fe (for P. trifoliata). Growth, the degree of chlorosis, the plant mineral composition, and the activity of the root ferric chelate-reductase (FCR) were assessed. Ceratonia plants exposed to 1 mu M Fe were efficient at using Fe in the synthesis of chlorophyll. The activity of FCR was enhanced in the total absence of Fe. In Poncirus a low activity of the FCR was observed in plants with no Fe. The balance between micronutrients in the Ceratonia roots was not affected with 1 mu M Fe compared with the higher Fe concentration treatments.

Large areas of land worldwide are estimated to be disturbed by mining activities, thereby contributing to severe environmental consequences. Mining represents one of the greatest transformations of the landscape caused by human activity and high concentrations of heavy metals in mine spoil can adversely impact microbial activity and plant establishment and subsequent revegetation success. Moreover, fly ash (FA), generated during the combustion of coal for energy production, is an industrial by-product, which is recognized as an environmental pollutant. However, several studies proposed that FA can be used as a soil additive that may improve physical, chemical, and biological properties of degraded soils and can act as a source of plant micro- and macronutrients. Furthermore, practical value of FA as an eco-friendly and economic soil amendment for the reclamation of acid mine spoils may be enhanced by coapplication with biosolids. Indeed, addition of biosolids could improve the success of reclamation/revegetation efforts.