Fungal and bacterial contributions to codenitrification emissions of N<Subscript>2</Subscript>O and N<Subscript>2</Subscript> following urea deposition to soil

Grazed pastures contribute significantly to anthropogenic emissions of N₂O but the respective contributions of archaea, bacteria and fungi to codenitrification in such systems is unresolved. This study examined the relative contributions of bacteria and fungi to rates of denitrification and codenitrification under a simulated ruminant urine event. It was hypothesised that fungi would be primarily responsible for both codenitrification and total N₂O and N₂ emissions. The effects of bacterial (streptomycin), fungal (cycloheximide), and combined inhibitor treatments were measured in a laboratory mesocosm experiment, on soil that had received ¹⁵N labelled urea. Soil inorganic-N concentrations, N₂O and N₂ gas fluxes were measured over 51 days. On Days 42 and 51, when nitrification was actively proceeding in the positive control, the inhibitor treatments inhibited nitrification as evidenced by increased soil NH ₄ ⁺ -N concentrations and decreased soil NO ₂ ^? -N and NO ₃ ^? -N concentrations. Codenitrification was observed to contribute to total fluxes of both N₂O (≥ 33%) and N₂ (≥ 3%) in urine-amended grassland soils. Cycloheximide inhibition decreased NH ₄ ⁺ –¹⁵N enrichment and reduced N₂O fluxes while reducing the contribution of codenitrification to total N₂O fluxes by ≥ 66 and ≥ 42%, respectively. Thus, given archaea do not respond to significant urea deposition, it is proposed that fungi, not bacteria, dominated total N₂O fluxes, and the codenitrification N₂O fluxes, from a simulated urine amended pasture soil.     

The role of TiO<Subscript>2</Subscript> layers deposited on YSZ on the electrochemical promotion of C<Subscript>2</Subscript>H<Subscript>4</Subscript> oxidation on Pt

The electrochemical promotion of Pt/YSZ and Pt/TiO₂/YSZ catalyst-electrodes has been investigated for the model reaction of C₂H₄ oxidation in an atmospheric pressure single chamber reactor, under oxygen excess between 280 and 375 °C. It has been found that the presence of a dispersed TiO₂ thin layer between the catalyst electrode and the solid electrolyte (YSZ), results in a significant increase of the magnitude of the electrochemical promotion of catalysis (EPOC) effect. The rate enhancement ratio upon current application and the faradaic efficiency values, were found to be a factor of 2.5 and 4 respectively, higher than those in absence of TiO₂. This significantly enhanced EPOC effect via the addition of TiO₂ suggests that the presence of the porous TiO₂ layer enhances the transport of promoting O²⁻ species onto the Pt catalyst surface. This enhancement may be partly due to morphological factors, such as increased Pt dispersion and three-phase-boundary length in presence of the TiO₂ porous layer, but appears to be mainly caused by the mixed ionic-electronic conductivity of the TiO₂ layer which results to enhanced O²⁻ transport to the Pt surface via a self-driven electrochemical promotion O²⁻ transport mechanism.     

Responses of Soil Microbial Communities in the Rhizosphere of Cucumber (Cucumis sativus L.) to Exogenously Applied p-Hydroxybenzoic Acid

Changes in soil biological properties have been implicated as one of the causes of soil sickness, a phenomenon that occurs in continuous monocropping systems. However, the causes for these changes are not yet clear. The aim of this work was to elucidate the role of p-hydroxybenzoic acid (PHBA), an autotoxin of cucumber (Cucumis sativus L.), in changing soil microbial communities. p-Hydroxybenzoic acid was applied to soil every other day for 10?days in cucumber pot assays. Then, the structures and sizes of bacterial and fungal communities, dehydrogenase activity, and microbial carbon biomass (MCB) were assessed in the rhizosphere soil. Structures and sizes of rhizosphere bacterial and fungal communities were analyzed by polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) and real-time PCR, respectively. p-Hydroxybenzoic acid inhibited cucumber seedling growth and stimulated rhizosphere dehydrogenase activity, MBC content, and bacterial and fungal community sizes. Rhizosphere bacterial and fungal communities responded differently to exogenously applied PHBA. The PHBA decreased the Shannon-Wiener index for the rhizosphere bacterial community but increased that for the rhizosphere fungal community. In addition, the response of the rhizosphere fungal community structure to PHBA acid was concentration dependent, but was not for the rhizosphere bacterial community structure. Our results indicate that PHBA plays a significant role in the chemical interactions between cucumber and soil microorganisms and could account for the changes in soil microbial communities in the continuously monocropped cucumber system.     

CAN SIMULTANEOUS INHIBITION OF SEEDLING GROWTH AND STIMULATION OF RHIZOSPHERE BACTERIAL POPULATIONS PROVIDE EVIDENCE FOR PHYTOTOXIN TRANSFER FROM PLANT RESIDUES IN THE BULK SOIL TO THE RHIZOSPHERE OF SENSITIVE SPECIES?

In order to demonstrate that allelopathic interactions are occurring, one must, among other things, demonstrate that putative phytotoxins move from plant residues on or in the soil, the source, through the bulk soil to the root surface, a sink, by way of the rhizosphere. We hypothesized that the incorporation of phytotoxic plant residues into the soil would result in a simultaneous inhibition of seedling growth and a stimulation of the rhizosphere bacterial community that could utilize the putative phytotoxins as a sole carbon source. If true and consistently expressed, such a relationship would provide a means of establishing the transfer of phytotoxins from residue in the soil to the rhizosphere of a sensitive species under field conditions. Presently, direct evidence for such transfer is lacking. To test this hypothesis, cucumber seedlings were grown in soil containing various concentrations of wheat or sunflower tissue. Both tissue types contain phenolic acids, which have been implicated as allelopathic phytotoxins. The level of phytotoxicity of the plant tissues was determined by the inhibition of pigweed seedling emergence and cucumber seedling leaf area expansion. The stimulation of cucumber seedling rhizosphere bacterial communities was determined by the plate dilution frequency technique using a medium containing phenolic acids as the sole carbon source. When sunflower tissue was incorporated into autoclaved (to reduce the initial microbial populations) soil, a simultaneous inhibition of cucumber seedling growth and stimulation of the community of phenolic acid utilizing rhizosphere bacteria occurred. Thus, it was possible to observe simultaneous inhibition of cucumber seedlings and stimulation of phenolic acid utilizing rhizosphere bacteria, and therefore provide indirect evidence of phenolic acid transfer from plant residues in the soil to the root surface. However, the simultaneous responses were not sufficiently consistent to be used as a field screening tool but were dependent upon the levels of phenolic acids and the bulk soil and rhizosphere microbial populations present in the soil. It is possible that this screening procedure may be useful for phytotoxins that are more unique than phenolic acids.     

Electrochemical synthesis,characterization and application of a microstructure Cu<Subscript>3</Subscript>(BTC)<Subscript>2</Subscript> metal organic framework for CO<Subscript>2</Subscript> and CH<Subscript>4</Subscript> separation

The electrochemical route is a promising and environmentally friendly technique for fabrication of metal organic frameworks (MOFs) due to mild synthesis condition, short time for crystal growth and ease of scale up. A microstructure Cu₃(BTC)₂ MOF was synthesized through electrochemical path and successfully employed for CO₂ and CH₄ adsorption. Characterization and structural investigation of the MOF was carried out by XRD, FE-SEM, TGA, FTIR and BET analyses. The highest amount of carbon dioxide and methane sorption was 26.89 and 6.63 wt%, respectively, at 298 K. The heat of adsorption for CO₂ decreased monotonically, while an opposite trend was observed for CH₄. The results also revealed that the selectivity of the developed MOF towards CO₂ over CH₄ enhanced with increase of pressure and composition of carbon dioxide component as predicted by the ideal adsorption solution theory (IAST). The regeneration of as-synthesized MOF was also studied in six consecutive cycles and no considerable reduction in CO₂ adsorption capacity was observed.     

Direct electrochemical reduction of Dy<Subscript>2</Subscript>O<Subscript>3</Subscript> in CaCl<Subscript>2</Subscript> melt

The electrochemical reduction of Dy₂O₃ in CaCl₂ melt was studied. The cyclic voltammetry, chronoamperometry, AC impedance and constant voltage electrolysis were employed. A single cathodic current peak in the cyclic voltammogram and one response semicircle in the AC impedance spectrum were observed, supporting a one-step electrochemical reduction mechanism of Dy₂O₃. No intermediates were observed by XRD, which confirmed the following electrochemical reduction sequence: Dy₂O₃ → Dy. The charge transfer resistances and the activation energies involved in the electrochemical reduction step of Dy₂O₃ were obtained by simulating the AC impedance spectra with equivalent circuits. The electrochemical reduction reaction of Dy₂O₃ is controlled by the charge transfer process at a low voltage range and by the diffusion process at a high voltage range.     

Electrochemical promotion of CO<Subscript>2</Subscript> hydrogenation on Rh/YSZ electrodes

The electrochemical promotion of the CO₂ hydrogenation reaction on porous Rh catalyst–electrodes deposited on Y₂O₃-stabilized-ZrO₂ (or YSZ), an O²⁻ conductor, was investigated under atmospheric total pressure and at temperatures 346–477 °C, combined with kinetic measurements in the temperature range 328–391 °C. Under these conditions CO₂ was transformed to CH₄ and CO. The CH₄ formation rate increased by up to 2.7 times with increasing Rh catalyst potential (electrophobic behavior) while the CO formation rate was increased by up to 1.7 times with decreasing catalyst potential (electrophilic behavior). The observed rate changes were non-faradaic, exceeding the corresponding pumping rate of oxygen ions by up to approximately 210 and 125 times for the CH₄ and CO formation reactions, respectively. The observed electrochemical promotion behavior is attributed to the induced, with increasing catalyst potential, preferential formation on the Rh surface of electron donor hydrogenated carbonylic species leading to formation of CH₄ and to the decreasing coverage of more electron acceptor carbonylic species resulting in CO formation.     

Effects of NH3 and urea on K distribution in root and rhizosphere of maize

The effects of NH₃ formed by urea hydrolysis on K distribution in maize roots and the rhizosphere were examined by electron probe x-ray microanalysis. Fresh weight of seedlings growing on calcareous soils was decreased by applying 200 ppm N as urea attributable to the inhibition of the development of root hairs and lateral roots. In the U-200 treatment, little K accumulated in the roots but K concentration in the rhizosphere soil increased. Such a pattern does not appear in roots receiving 200 ppm as ammonium sulfate or on calcareous soils with 100 ppm N as urea or with 200 ppm as urea in an acidic clay loam. The results indicate that K efflux is responsible for the growth depression and that K efflux from the high concentration of NH₃ formed when urea is hydrolysed rather than from the NH ₄ ⁺ ion. Applying K fertilizer with urea should alleviate the adverse effects of urea on plant growth on calcareous soils by improving K status of the plant and by the decrease in rhizosphere soil pH which considerably reduces NH₃ concentration. Management designed to limit pH increase during urea hydrolysis should both prevent NH₃ injury and reduced N losses.     

Synthesis and Electrochemical Properties of LaCr<Subscript>1−x</Subscript>Co<Subscript>x</Subscript>O<Subscript>3</Subscript> (0 ≤ x ≤ 0.5) via Co-precipitation Method

Perovskite LaCr_1?xCo_xO₃ (0 ≤ x ≤ 0.5) oxides synthesized by co precipitation method were investigated. X-ray diffraction, thermo gravimetric and differential thermal analysis, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM) and electrochemical measurements, were used to characterize the structure, morphology, electrochemical properties of the samples. The studied compounds have orthorhombic and rhombohedral systems in the ranges (0 ≤ x ≤ 0.2) and (0.3 ≤ x ≤ 0.5) respectively. Thermal analysis results indicate that the pure phase was obtained at temperature above 800 °C. The structure and morphology of the samples characterized by SEM measurements indicate that particles have nearly spherical shapes and are agglomerated. The electrochemical measurements indicate that the catalytic activity is strongly influenced by cobalt doping. The highest electrode performance is achieved with large cobalt content.     

Investigations under real operating conditions of the electrochemical promotion by O<Subscript>2</Subscript> temperature programmed desorption measurements

The origin of the electrochemical promotion of catalysis (EPOC) was investigated via oxygen temperature-programmed desorption (O₂-TPD) from a polycrystalline Pt film interfaced with YSZ. TPD experiments were carried out under operating conditions similar to those used for catalytic activity measurements. This study has clearly shown that an anodic current generates the migration of “backspillover” ionic oxygen species from YSZ toward the Pt surface. These ionic species act as promoters and enable the formation of weakly adsorbed oxygen species coming from the gas phase which are more reactive and thus responsible for the activity enhancement. The effect of polarization is to carry or to remove the promoting ionic species on the Pt surface. Therefore, electrochemical promotion of catalysis can be considered as an electrically controlled metal support interaction, where the support is an O²⁻ conducting solid electrolyte.     

Synthesis and electrochemical evaluation of carbon coated Cu<Subscript>6</Subscript>Sn<Subscript>5</Subscript> alloy-graphite composite lithium battery anodes

With a view to minimize the unavoidable large volume changes of tin based Cu₆Sn₅ alloy anodes, a composite Cu₆Sn₅/graphite anode has been prepared via. a mechanical alloying process and subsequently coated with disordered carbon through pyrolysis of PVC. Phase pure products with better crystallinity and preferred surface morphology were obtained, as evident from PXRD and SEM respectively. Upon electrochemical charge-discharge, the intermetallic Cu₆Sn₅ alloy-graphite composite anode was found to exhibit an enhanced initial discharge capacity of 564 mAh g⁻¹ followed by significant capacity fade (>20%) especially after five cycles. On the other hand, carbon coated Cu₆Sn₅ alloy-graphite composite demonstrated promising electrochemical properties such as steady reversible capacity (∼200 mAh g⁻¹), excellent cycle performance (<5% capacity fade) and high coulombic efficiency (∼98%) via. significant reduction of volume changes. The carbon coating offers buffering and conductive actions on the anode active material and thereby enhances the electrochemical behavior of carbon coated Cu₆Sn₅ alloy/graphite composite anode material.     

Electrochemical treatment of ammonia in wastewater by RuO<Subscript>2</Subscript>–IrO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>/Ti electrodes

This study investigated the removal of ammonia in wastewater by an electrochemical method using titanium electrodes coated with ruthenium and iridium (RuO₂–IrO₂–TiO₂/Ti) with low chlorine evolution over-voltage. The effects of operating parameters, including chloride ion concentration, current density and initial pH, were also investigated. The results were evaluated primarily by considering the efficiency of the elimination of NH₄⁺-N. The removal of ammonia by electrochemical oxidation mainly resulted from the indirect oxidation effect of chlorine/hypochlorite produced during electrolysis. The direct anodic oxidation efficiency of ammonia was less than 5%, and the current efficiency was less than 10%. The ammonia removal followed pseudo-first-order kinetics. The electrochemical process can be applied successfully as a final polishing step, or as an alternative method to biological nitrification. The process seems to be most beneficial for small coastal cities     

Impacts of Water Table Management on N<Subscript>2</Subscript>O and N<Subscript>2</Subscript> from a Sandy Loam Soil in Southwestern Quebec,Canada

Nitrous oxide (N₂O) is primarily produced as intermediate in denitrification and, to a lesser extent, through nitrification processes. Nitrous oxide emission and, consequently, its atmospheric impacts depend on the extent to which N₂O is reduced to dinitrogen gas (N₂) by denitrifiers. Field experiments were conducted from 1998 through 2000 growing seasons at St. Emmanuel, Quebec, Canada, to investigate the combined impact of water table management (WTM) and N fertilization rate on the soil denitrification (N₂O + N₂) rate, rate of N₂O production, and the N₂O:N₂O + N₂ ratio. Water table treatments included subirrigation (SI) with a target water table depth of 0.6 m and free drainage (FD) with open drains. The tile drains (75 mm diameter) were laid at a 1.0 m depth from the soil surface. Nitrogen fertilizer was applied at two rates:120 and 200 kg N ha⁻¹ as ammonium nitrate (34-0-0). The N₂O + N₂ evolution rates were greater in SI (12.9 kg N ha⁻¹) than in FD (5.8 kg N ha⁻¹) plots. The percentages of N₂O relative to overall N₂O + N₂ evolution were 35 and 11% for 1998, 29 and 8% for 1999, and 37 and 20% for 2000, under FD and SI, respectively. The reduced N₂O production under SI was due to a greater reduction of N₂O to N₂. Results indicate that greater N₂O + N₂ evolution under shallow water tables are not necessarily accompanied by higher N₂O emissions.     

Structural characterization and electrochemical properties of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> anode materials synthesized by a hydrothermal method

Cobalt oxide [Co₃O₄] anode materials were synthesized by a simple hydrothermal process, and the reaction conditions were optimized to provide good electrochemical properties. The effect of various synthetic reaction and heat treatment conditions on the structure and electrochemical properties of Co₃O₄ powder was also studied. Physical characterizations of Co₃O₄ are investigated by X-ray diffraction, scanning electron microscopy, and Brunauer-Emmett-Teller [BET] method. The BET surface area decreased with values at 131.8 m²/g, 76.1 m²/g, and 55.2 m²/g with the increasing calcination temperature at 200°C, 300°C, and 400°C, respectively. The Co₃O₄ particle calcinated at 200°C for 3 h has a higher surface area and uniform particle size distribution which may result in better sites to accommodate Li⁺ and electrical contact and to give a good electrochemical property. The cell composed of Super P as a carbon conductor shows better electrochemical properties than that composed of acetylene black. Among the samples prepared under different reaction conditions, Co₃O₄ prepared at 200°C for 10 h showed a better cycling performance than the other samples. It gave an initial discharge capacity of 1,330 mAh/g, decreased to 779 mAh/g after 10 cycles, and then showed a steady discharge capacity of 606 mAh/g after 60 cycles.     

Effects of K<Subscript>4</Subscript>Fe(CN)<Subscript>6</Subscript> on electroless copper plating using hypophosphite as reducing agent

K₄Fe(CN)₆ was used to improve the microstructure and properties of copper deposits obtained from hypophosphite baths. In electroless copper plating solutions using hypophosphite as the reducing agent, nickel ions (0.0038 M with Ni²⁺/Cu²⁺ mole ratio 0.12) was used to catalyze hypophosphite oxidation. However, the color of the copper deposits was dark or brown and its resistivity was much higher than that obtained in formaldehyde baths. The effects of K₄Fe(CN)₆ on the deposit composition, resistivity, structure, morphology and the electrochemical reactions of hypophosphite (oxidation) and cupric ion (reduction) have been investigated. The deposition rate and the resistivity of the copper deposits decreased significantly with the addition of K₄Fe(CN)₆ to the plating solution and the color of the deposits changed from dark-brown to copper-bright with improved uniformity. The nickel and phosphorus content in the deposits also decreased slightly with the use of K₄Fe(CN)₆. Smaller crystallite size and higher (111) plane orientation were obtained by addition of K₄Fe(CN)₆. The electrochemical current–voltage results show that K₄Fe(CN)₆ inhibited the catalytic oxidation of hypophosphite at active nickel sites and reduced the reduction reaction of cupric ions on the deposit surface by adsorption on the electrode. This results in lower deposition rate and a decrease in the mole ratio of NaH₂PO₂/CuSO₄ consumed during plating.     

N<Subscript>2</Subscript>O fluxes and CO<Subscript>2</Subscript> exchange at different N doses under elevated CO<Subscript>2</Subscript> concentration in boreal agricultural mineral soil under <Emphasis Type="Italic">Phleum pratense</Emphasis>

The effects of elevated atmospheric CO₂ concentration on N₂O fluxes, instant CO₂ exchange and the biomass production of timothy (Phleum pratense) were studied in the laboratory. Three sets of 12 farmed sandy soil mesocosms sown with Phleum pratense were fertilised with a commercial fertiliser in order to add 5, 10 and 15 g N m⁻², and equally distributed in four thermo-controlled greenhouses. In two of the greenhouses, the CO₂ concentration was kept at atmospheric concentration (360 μmol mol⁻¹), and in the other two at double the ambient concentration (720 μmol mol⁻¹). Forage was harvested and the plants fertilised twice during the N₂O measurements. This was followed by an extra fertilisation and harvesting. After the third harvest, the growth of P. pratense was maintained at a height of 18 cm for measurements of instant CO₂ exchange, performed in two growth chambers. N₂O exchange was monitored using a closed chamber technique and a gas chromatograph. Instant CO₂ exchange was monitored using an infrared gas analyser. N₂O was emitted from the soil in the low, moderate and high N treatments at both CO₂ concentrations when the moisture content was low, the N₂O probably being mainly derived from nitrification. The highest flux (3303 μg N₂O m⁻² h⁻¹) occurred in the highest N treatment before thinning the stand of P. pratense under elevated CO₂ concentration. P. pratense was acclimated to the elevated CO₂ concentration: the NEE and P _G of the elevated growth of P. pratense decreased, in contrast to the fluxes of the normal ambient growth, when measured at the changed CO₂ concentration (ambient). The rate of respiration (R _TOT) in the agroecosystem did not increase due to the elevated CO₂ concentration, but instead the results indicated decreased R _TOT (on average 2049 and 1808 mg CO₂ m⁻² h⁻¹ at ambient and elevated CO₂ concentration, respectively) when there was an abundant N supply. This infers the possibility of enhanced C accumulation in agriculture mineral soil via P. pratense under an increased atmospheric CO₂ supply.     

Natural and NH<Subscript>4</Subscript><Superscript>+</Superscript>-enriched zeolitite amendment effects on nitrate leaching from a reclaimed agricultural soil (Ferrara Province,Italy)

In this paper we report an overview of the main outcomes of a 3-years experimental cultivation carried out in an Italian reclaimed agricultural field amended with different types of zeolitites (rock containing > 50% of zeolites), under cereals cultivation (Sorghum vulgare Pers, Zea mays and Triticum durum). The aim of the experiment was to exploit the properties of zeolite-rich volcanic rocks (zeolitites) for reducing the excessively high NO₃^? content in the soil and in waters flowing out the sub-surface drainage system of the field and flushing into the surface water system, reducing concomitantly also chemical fertilization application rates (up to 50%). Zeolitites were tested both in their natural state and in a NH₄⁺-enriched form, obtained through an enrichment process with NH₄⁺-rich zoo-technical effluents (pig slurry). NO₃^? content in soils and in waters discharged through SSDS were periodically monitored during the experimentation and crop yield quantified. Results showed that, for three consecutive cultivation cycles, the overall NO₃^? concentrations in water extracts was reduced by 45% in the zeolitite treated soils, while in SSDS waters the reduction reached the 64%. Notwithstanding the lower N input from chemical fertilizers, crop yield was not negatively affected in the zeolitite amended soils with respect to the control. Zeolitite addition increased thus soil NH₄⁺ retention and probably influenced several pathways of N losses, allowing a better fertilizer use efficiency by plants and a reduction of the overall NO₃^? concentrations in the surface waters.     

Temperature programmed desorption of oxygen from Pd films interfaced with Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-doped ZrO<Subscript>2</Subscript>

The origin of the effect of non-faradaic electrochemical modification of catalytic activity (NEMCA) or Electrochemical Promotion was investigated via temperature-programmed-desorption (TPD) of oxygen, from polycrystalline Pd films deposited on 8 mol%Y₂O₃–stabilized–ZrO₂ (YSZ), an O²⁻ conductor, under high-vacuum conditions and temperatures between 50 and 250 °C. Oxygen was adsorbed both via the gas phase and electrochemically, as O²⁻, via electrical current application between the Pd catalyst film and a Au counter electrode. Gaseous oxygen adsorption gives two adsorbed atomic oxygen species desorbing at about 300 °C (state β₁) and 340–500 °C (state β₂). The creation of the low temperature peak is favored at high exposure times (exposure >1 kL) and low adsorption temperatures (T_ads < 200 °C). The decrease of the open circuit potential (or catalyst work function) during the adsorption at high exposure times, indicates the formation of subsurface oxygen species which desorbs at higher temperatures (above 450 °C). The desorption peak of this subsurface oxygen is not clear due to the wide peaks of the TPD spectra. The TPD spectra after electrochemical O²⁻ pumping to the Pd catalyst film show two peaks (at 350 and 430 °C) corresponding to spillover O_ads and according to the reaction:

Soil and Soilless Tomato Cultivation Promote Different Microbial Communities That Provide New Models for Future Crop Interventions

The cultivation of soilless tomato in greenhouses has increased considerably, but little is known about the assembly of the root microbiome compared to plants grown in soil. To obtain such information, we constructed an assay in which we traced the bacterial and fungal communities by amplicon-based metagenomics during the cultivation chain from nursery to greenhouse. In the greenhouse, the plants were transplanted either into agricultural soil or into coconut fiber bags (soilless). At the phylum level, bacterial and fungal communities were primarily constituted in all microhabitats by Proteobacteria and Ascomycota, respectively. The results showed that the tomato rhizosphere microbiome was shaped by the substrate or soil in which the plants were grown. The microbiome was different particularly in terms of the bacterial communities. In agriculture, enrichment has been observed in putative biological control bacteria of the genera Pseudomonas and Bacillus and in potential phytopathogenic fungi. Overall, the study describes the different shaping of microbial communities in the two cultivation methods.     

Biological System for Improving the Availability of Tilemsi Phosphate Rock for Wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) Cultivated in Mali

The Tilemsi phosphate rock (TPR) of Mali is a good and cheaper alternative to imported phosphate fertilizers. Many soil microorganisms can also mobilize sparingly soluble inorganic phosphates, and several have a good potential to improve plant growth. With the aim of improving the response of wheat cultivated in Mali to fertilization with TPR, in this work we describe the isolation and selection from four different Malian soils of TPR-solubilizing microorganisms (TSM) with high P-mobilization activities. When the rhizosphere of three wheat cultivars (Alkama Beri, Hindi Tossom and Tetra) was used to isolate TSM, only bacterial isolates were selected. TPR-solubilizing fungi were only obtained by soil enrichment in liquid medium containing TPR as sole P source. In the rhizosphere a significant correlation was observed between the total microbial population and the number of microorganisms solubilizing TPR. No such correlation was observed in the rhizoplane. Initially 44 bacteria and 18 fungi were selected, but after 10 subcultures on agar plates and a liquid medium, only 6 bacteria and 2 fungi retained their high P solubilizing trait. A field inoculation trial was established during the growing season 2000–2001 in Koygour. Wheat cv. Tetra was inoculated with the 8 selected TSM (6 bacteria and 2 fungi) and fertilized with 30 kg ha⁻¹ P added as TPR or diammonium phosphate (DAP). The growth parameters measured were plant height at 30 and 60 days, the number of leaves per main stem at 60 days, and root and shoot dry matter yields 60 days after planting. Root colonization by indigenous arbuscular mycorrhizas (AM) was also measured in 45-day-old plants. Significant interactions were observed between TSM inoculation and P-fertilization for root colonization with AM, plant height at 30 days and root dry matter yield. The bacterial isolate Pseudomonas sp. BR2, which appeared to be a mycorrhiza helper bacterium, significantly enhanced wheat seedling emergence very early (5 days after planting) under field condition, and caused 128% increase in root dry matter yield. The two TPR-solubilizing fungal isolates Aspergillus awamori Nakazawa C1 and Penicillium chrysogenum Thom C13 also caused respectively 60 and 44% increases in root dry matter yields. The choice of the TSM BR2, C1 and C13 for further field trials is discussed.