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Abstract Amidst the challenges posed by climate change, exploring advanced technologies like nanotechnology is crucial for enhancing agricultural productivity and food security. Consequently, this study investigated the impact of nano SiO2 (nSiO2), nano TiO2 (nTiO2) and SiO2/TiO2 nanocomposites (NCs) on 30-day-old Zea mays L. plants and soil health at concentrations of 100 and 200 ppm. Results showed that nSiO2 and nTiO2 at 100 ppm and SiO2/TiO2 NCs at both concentrations, positively influenced plant growth, with the best stimulation observed at 200 ppm of SiO2/TiO2 NCs. Improved plant growth was associated with higher chlorophyll content, photosynthetic rate, transpiration rate, stomatal conductance, rhizospheric N-fixing and phosphate solubilizing bacterial population and plant nutrient uptake. Additionally, treated plants exhibited increased cellulose and starch levels. Malondialdehyde (MDA) content was lower or similar to that of the control, except at 200 ppm of nTiO2-treated shoots. Antioxidant enzyme activities fluctuated, indicating physiological adjustments. Overall, 100 ppm of nTiO2 as well as nSiO2 and 100 and 200 ppm of SiO2/TiO2 NCs improved soil fertility and Z. mays growth, suggesting potential benefits for sustainable agriculture. The findings lay the foundation for more comprehensive investigations into the long-term fate of nanomaterials in soil and their intricate molecular-level interactions with Z. mays.

Amidst the challenges posed by climate change, exploring advanced technologies like nanotechnology is crucial for enhancing agricultural productivity and food security. Consequently, this study investigated the impact of nano SiO2 (nSiO2), nano TiO2 (nTiO2) and SiO2/TiO2 nanocomposites (NCs) on 30-day-old Zea mays L. plants and soil health at concentrations of 100 and 200 ppm. Results showed that nSiO2 and nTiO2 at 100 ppm and SiO2/TiO2 NCs at both concentrations, positively influenced plant growth, with the best stimulation observed at 200 ppm of SiO2/TiO2 NCs. Improved plant growth was associated with higher chlorophyll content, photosynthetic rate, transpiration rate, stomatal conductance, rhizospheric N-fixing and phosphate solubilizing bacterial population and plant nutrient uptake. Additionally, treated plants exhibited increased cellulose and starch levels. Malondialdehyde (MDA) content was lower or similar to that of the control, except at 200 ppm of nTiO2-treated shoots. Antioxidant enzyme activities fluctuated, indicating physiological adjustments. Overall, 100 ppm of nTiO2 as well as nSiO2 and 100 and 200 ppm of SiO2/TiO2 NCs improved soil fertility and Z. mays growth, suggesting potential benefits for sustainable agriculture. The findings lay the foundation for more comprehensive investigations into the long-term fate of nanomaterials in soil and their intricate molecular-level interactions with Z. mays. [ABSTRACT FROM AUTHOR]

Abstract The present study was conducted to determine the efficiency of organomineral fertilizer from cupuaçu residues (ORFCup) and dose of maximum technical efficiency of Azospirillum brasilense on the initial growth and morphophysiological quality of Mezilaurus itauba seedlings in the northern Amazon. The variables evaluated were: shoot height (H, cm), stem diameter (SD, mm), shoot dry mass (SDM, g plant-1), root dry mass (RDM, g plant-1) total dry mass (TDM, g plant-1), Dickson quality index (DQI), net assimilation rate (NAR, g m-2 day-1), leaf relative growth rate (RGR, g m-2 day-1), leaf area ratio (LAR, m2 g-1), leaf relative growth rate (RGR, g m-2 day-1), leaf area ratio (LAR, m2 g-1), specific leaf area (SLA, cm2 g-1), and leaf mass ratio (LMR, g g-1). Organomineral fertilizer from cupuaçu residues promotes better quality and robustness in M. itauba seedlings at the dose of maximum technical efficiency of 0.45 mL. L-1 of A. brasilense.

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Background: Tree mycorrhizal types (arbuscular mycorrhizal fungi and ectomycorrhizal fungi) alter nutrient use traits and leaf physicochemical properties and, thus, affect leaf litter decomposition. However, little is known about how different tree mycorrhizal species affect the microbial diversity, community composition, function, and community assembly processes that govern leaf litter-dwelling microbes during leaf litter decomposition. Methods: In this study, we investigated the microbial diversity, community dynamics, and community assembly processes of nine temperate tree species using high-resolution molecular technique (Illumina sequencing), including broadleaved arbuscular mycorrhizal, broadleaved ectomycorrhizal, and coniferous ectomycorrhizal tree types, during leaf litter decomposition. Results and discussion: The leaves and needles of different tree mycorrhizal types significantly affected the microbial richness and community composition during leaf litter decomposition. Leaf litter mass loss was related to higher sequence reads of a few bacterial functional groups, particularly N-fixing bacteria. Furthermore, a link between bacterial and fungal community composition and hydrolytic and/or oxidative enzyme activity was found. The microbial communities in the leaf litter of different tree mycorrhizal types were governed by different proportions of determinism and stochasticity, which changed throughout litter decomposition. Specifically, determinism (mainly variable selection) controlling bacterial community composition increased over time. In contrast, stochasticity (mainly ecological drift) increasingly governed fungal community composition. Finally, the co-occurrence network analysis showed greater competition between bacteria and fungi in the early stages of litter decomposition and revealed a contrasting pattern between mycorrhizal types. Conclusion: Overall, we conclude that tree mycorrhizal types influence leaf litter quality, which affects microbial richness and community composition, and thus, leaf litter decomposition. [ABSTRACT FROM AUTHOR]

Rice is an important staple crop influenced by rising CO2 and related climate change, but it is not well-known how N-fixing Azotobacter affects rice growth and yield under different CO2 concentrations. This study aimed to determine the effects of Azotobacter strains on the growth and yield of rice plants grown in two paddy soils under varying CO2 conditions. Rice plants inoculated with three Azotobacter strains were grown in a conventional rice soil (Dali) and an organic rice soil (Houlong) under 500 or 1000 ppm CO2. These three Azotobacter strains significantly increased the harvest index of rice plants grown in Dali soil under 1000 ppm CO2, but they did not significantly increase the harvest index for rice plants grown in Houlong soil under elevated CO2. Interestingly, only A. beijerinckii CHB 461 significantly promoted the thousand-grain weight of rice plants grown in both Dali and Houlong soils under elevated CO2. Dali soil had a high level of soil organic matter, exchangeable Ca and Mg, and available Cu and Zn, probably resulting in a better response of the rice plants to Azotobacter inoculation under elevated CO2. In conclusion, in the application of Azotobacter to promote rice growth and yield under future rising CO2 conditions, the soil properties and characteristics of Azotobacter strains may need to be considered. [ABSTRACT FROM AUTHOR]

Due to concerns about the adverse effects of synthetic pesticides on the environment and human health, there is a growing preference for environmentally friendly and safe pesticides. However, hard evidence to verify their low-risk characteristics is scarce. This work attempted to compare the effects of a chemical pesticide (alpha-cypermethrin) and a biopesticide (emamectin benzoate) on the growth of indigenous nitrogen-fixing bacteria. These bacterial strains were isolated from the rhizosphere of bean plant samples obtained from farmers' fields where these two pesticides were sprayed on bean crops. The results revealed that at the field-recommended concentration of both pesticides, the growth of the isolates in both nutrient-rich and nitrogen-free media remained largely unaffected. However, the bacteria's absolute growth inhibition was recorded as the pesticide concentration increased. When the Tryptic Soy Broth medium was supplemented with a pesticide concentration 10 times higher than the recommended dose, up to 85.7% of the isolated strains were completely inhibited in growth when exposed to alpha-cypermethrin. In contrast, only 17.9% of bacterial strains were completely inhibited when exposed to emamectin benzoate. In a nitrogen-free medium, the proportion of inhibited bacteria was absolute when the medium was supplemented with alpha-cypermethrin and emamectin benzoate at a dosage 10 times higher than the recommended concentration, which reached 92.9% and 28.6%, respectively. The strains that exhibited higher tolerance to both pesticides were identified as Niallia nealsonii ND15 and Rhizobium subbaraonis ND27. Our findings emphasize the importance of minimizing pesticide accumulation in the soil to protect the viability of soil-beneficial bacteria and ensure soil quality for safe and sustainable crop production. [ABSTRACT FROM AUTHOR]

BackgroundTree mycorrhizal types (arbuscular mycorrhizal fungi and ectomycorrhizal fungi) alter nutrient use traits and leaf physicochemical properties and, thus, affect leaf litter decomposition. However, little is known about how different tree mycorrhizal species affect the microbial diversity, community composition, function, and community assembly processes that govern leaf litter-dwelling microbes during leaf litter decomposition. MethodsIn this study, we investigated the microbial diversity, community dynamics, and community assembly processes of nine temperate tree species using high-resolution molecular technique (Illumina sequencing), including broadleaved arbuscular mycorrhizal, broadleaved ectomycorrhizal, and coniferous ectomycorrhizal tree types, during leaf litter decomposition.Results and discussionThe leaves and needles of different tree mycorrhizal types significantly affected the microbial richness and community composition during leaf litter decomposition. Leaf litter mass loss was related to higher sequence reads of a few bacterial functional groups, particularly N-fixing bacteria. Furthermore, a link between bacterial and fungal community composition and hydrolytic and/or oxidative enzyme activity was found. The microbial communities in the leaf litter of different tree mycorrhizal types were governed by different proportions of determinism and stochasticity, which changed throughout litter decomposition. Specifically, determinism (mainly variable selection) controlling bacterial community composition increased over time. In contrast, stochasticity (mainly ecological drift) increasingly governed fungal community composition. Finally, the co-occurrence network analysis showed greater competition between bacteria and fungi in the early stages of litter decomposition and revealed a contrasting pattern between mycorrhizal types.ConclusionOverall, we conclude that tree mycorrhizal types influence leaf litter quality, which affects microbial richness and community composition, and thus, leaf litter decomposition.

Rice farming is hampered by saline soil, which contains a large amount of soluble salt. The high salt content inhibits plant growth and causes nitrogen nutrient deficiency, as well as sodium and chlorine ion poisoning. Beneficial microbes that have adapted to saline ecosystems (halotolerant) can reduce salinity's impact on rice growth. Microorganisms known as halotolerant bacteria can survive in high salt environments by maintaining an osmotic balance. The use of halotolerant N-fixing bacteria (HNB) as biofertilizers is an attempt to boost nitrogen nutrients and rice plant productivity in saline land. The goal of this study was to see how effective HNB isolates were at increasing rice plant growth. The experiment was conducted in the greenhouse of Universitas Padjadjaran's Faculty of Agriculture, using a randomized block design with 16 treatments (control, single, and consortia of inoculant) and was repeated three times. Rice seedlings were inoculated with HNB isolates and grown in a Fahraeus saline medium. The HNB consortium application increased plant height by 9.03 cm, root-shoot ratio by 0.92, IAA content by 0.475 g/mL, nitrogen content by 2.94%, and the total number of HNB isolates (Azotobacter, Azospirillum, Bacillus, and Stenotrophomonas) by 8.10x107 CFU/mL. [ABSTRACT FROM AUTHOR]

Background: Bio-based and biodegradable plastics are considered as plastics of the future owing to their ability to decompose under various environmental conditions. However, their effects on the soil microbiome are poorly characterised. In this study, we aimed to investigate the effects of an important bio-based and biodegradable plastic, polybutylene succinate-co-adipate (PBSA), on soil microbial diversity and community composition using high-resolution molecular technique (Illumina sequencing) targeting all three microbial domains: archaea, bacteria, and fungi. Results: Adding high load of PBSA to soil (6% (w/w)) caused a significant decline in archaeal (13%) and fungal (45%) richness and substantial changes in both bacterial (Proteobacteria, Actinobacteria, and Acidobacteria) and fungal (Eurotiomycetes, Sordariomycetes, Leotiomycetes, and Dothideomycetes) community composition compared with no PBSA addition to soil. The combined effects of PBSA and (NH4)2SO4 fertilisation on the soil microbiome were much greater than the effects of PBSA alone. We only detected opportunistic human pathogens in low abundance on PBSA and in the surrounding soil. However, some plant pathogenic fungi were detected and/or enriched on the PBSA films and in surrounding soil. Apart from plant pathogens, many potential microbial control agents and plant growth-promoting microorganisms were also detected/enriched owing to PBSA addition. Adding high load of PBSA together with (NH4)2SO4 fertilisation can either eliminate some plant pathogens or enrich specific pathogens, especially Fusarium solani, which is economically important. Conclusions: We conclude that high load of bio-based and biodegradable PBSA plastic may negatively affect soil microbiome. [ABSTRACT FROM AUTHOR]

Soil nitrogen (N)‐fixing bacteria community plays an important role in the N cycling process in soil, but there is still limited information about how the soil microbes that drive this process to respond to combined application of tillage and crop residue management under the double‐cropping rice (Oryza sativa L.) paddy field in southern of China. Therefore, the effects of 6‐years short‐term tillage treatment on soil N‐fixing bacteria community under the double‐cropping rice paddy field in southern China were studied by using the polymerase chain reaction‐denaturing gradient gel electrophoresis method. The field experiment included four tillage treatments: conventional tillage with crop residue incorporation (CT), rotary tillage with crop residue incorporation (RT), no‐tillage with crop residue retention (NT), rotary tillage with crop residue removed as control (RTO). The results showed that the diversity index and richness index of cbbLR and nifH genes with CT, RT, and NT treatments were increased, compared with RTO treatment. Compared with RTO treatment, the abundance of cbbLR gene with CT, RT, and NT treatments were increased by 6.54, 4.73, and 2.78 times, respectively. Meanwhile, the abundance of nifH gene with CT, RT, and NT treatments were 5.32, 3.71, and 2.45 times higher than that of RTO treatment. The results also indicated that soil autotrophic Azotobacter and nitrogenase activity with CT and RT treatments were significantly higher (p <.05) than that of RTO treatment. There was an obvious difference in characteristic of soil N‐fixing bacteria community between the application of crop residue and without crop residue input treatments. In summary, the results indicated that the abundance of N‐fixing bacteria community in the double‐cropping rice paddy field increased with conventional tillage and rotary tillage practice. [ABSTRACT FROM AUTHOR]

Vachellianilotica (L.) Willd. Ex Del. is a multipurpose leguminous tree that is common in grassland and savanna ecosystems in southern and eastern Africa. These ecosystem soils are reported to be acidic and nutrient-limited, specifically with regards to nitrogen (N) and phosphorus (P). The presence of this plant in these terrestrial ecosystems improves soil fertility benefiting the surrounding vegetation due to its ability to fix atmospheric N. This study seeks to understand the N-fixing bacteria symbiosis and physiological adaptations of V. nilotica in these acidic and nutrient-deficient KwaZulu-Natal soils. The soils used for this study were collected from the Ukulinga Grassland Nutrient Experiment located at the Ukulinga research farm of the University of KwaZulu-Natal, Pietermaritzburg, South Africa. Due to long-term soil nutrient addition treatments, these soils offered a diverse nutrient variation for better understanding the effects of acidity and nutrient variation on microbial symbiosis, plant nutrition, and biomass accumulation of V. nilotica. V. nilotica was able to maintain growth by relying on both atmospheric and soil-derived N across all treatments decreasing carbon (C) growth costs. There was an increased reliance on atmospheric-derived N of un-nodulated high N-treated plants. The plants grown in high N + P soils were able to nodulate with various species from the Mesorhizobium genus, which resulted in increased biomass compared to other plants. The results of this study show that V. nilotica can alter N sources to reduce C growth costs. In addition, both nodulating and free-living soil N2 fixing bacteria such as Caulobacter rhizosphaerae, Sphingomonas sp. and Burkholderia contaminans identified in the experimental soils may play an important role under P-deficient conditions.

The rapid development of cities in the recent 10 years caused a reduction in the cultivated land area, which only accounts for 14% of the total land area in China. Land development and reclamation have been regarded as an effective way to compensate farmland occupation. However, most of the newly reclaimed land has poor soil fertility and suitability; in some cases, the production capacity is only 10–30% of the occupied farmland. In order to ameliorate the soil quality of the newly reclaimed land, this study evaluated the effects of commercial organic fertilizer (0.75, 1.50, and 2.25 kg/m2), mushroom residue (1.50, 2.25, and 3.00 kg/m2), biogas slurry (150, 225, and 300 kg/m2), vegetable cake (0.30 and 0.60 kg/m2), and chemical compound fertilizer (37.50 g/m2) on the pH, moisture content and organic matter content (OMC), available phosphate, total nitrogen, alkaline hydrolysis nitrogen, microbial biomass carbon and nitrogen, and number of total bacteria and phosphate-solubilizing bacteria, as well as the growth of maize seedlings. The results from this study indicate that the soil quality (OMC is an indicator) was ameliorated by chemical and organic fertilizers, in particular commercial organic fertilizers, which caused a 9.35–16.35% increase in moisture content, a 11.56–18.72% increase in pH, a 1.73–2.15 fold increase in OMC, a 338.44–491.41% increase in available P, a 36.80–48.14% increase in total N, a 95.32–128.34% increase in alkaline hydrolysis N, a 92.57–178.38% increase in total bacterial numbers, and a 7.57–20.87 fold increase in microbial biomass carbon compared with the control. The pot experiment further indicated that soil amended with commercial organic fertilizers caused a 20.35–30.55% increase in the height and a 12.50–16.67% increase in the total dry weight of maize seedlings. In addition, representative strains with the ability to dissolve phosphorus and fix nitrogen were successfully isolated using the culture method, and were then identified based on colony morphological observation and 16S rDNA sequence analysis, which help us to not only understand why organic fertilizer has great effect on soil improvement, but also provides beneficial microbial resources for further study.

The evaluation of the impact of oil on the soil-root interaction of the white mangrove plant, Laguncularia racemosa is essential to identify changes in microbial activity and biotechnological potential for remediation contaminated Histosols. The objective was to evaluate the spatial distribution of total petroleum hydrocarbons (THP) in organic soil, the population density of plant growth promoting bacteria, also in microbial respiration in the rhizoplane (RI), rhizosphere (RZ) and in non-rhizospheric soil (NRS) of L. racemosa. An area of 8 000 m2 of an affected Histosol was evaluated, during 1967 and 1968, by chronic oil spill and drilling mud from the La Venta 248 oil well. Fifteen trees of this species were selected to obtain samples of the RI, RZ and NRS. The TPH were extracted in soxhlet with dichloromethane for eight hours and quantified by gravimetry. The average amount extracted from TPH allowed the differentiation of four soils (S) from the evaluated area, the average values were for S1: 1 797 mg kg-1 (not contaminated for Mexican regulations) and three contaminated soils, the values are S2: 3 294, S3: 5 249, and S4: 10 389 mg kg-1. The results show statistical differences (Duncan, p ≤ 0.05) between means of the evaluated variables. The greatest accumulation of TPH was 22 962 mg kg-1, it was extracted from the NRS in S4. The highest densities of N-fixing bacteria (NFB), P solubilizers, Azospirillum and Azotobacter were biostimulated by the presence of high levels of THP in the soil, however microbial respiration was inhibited. The results suggest that L. racemosa is sustainable in soils with weathering oil, and is a biostimulator of microbial activity for natural attenuation.. [ABSTRACT FROM AUTHOR]

Bradyrhizobium diazoefficiens CPAC 7 and Bradyrhizobium japonicum CPAC 15 are broadly used in commercial inoculants in Brazil, contributing to most of the nitrogen required by the soybean crop. These strains differ in their symbiotic properties: CPAC 7 is more efficient in fixing nitrogen, whereas CPAC 15 is more competitive. Comparative genomics revealed many transposases close to genes associated with symbiosis in the symbiotic island of these strains. Given the importance that insertion sequences (IS) elements have to bacterial genomes, we focused on identifying the local impact of these elements in the genomes of these and other related Bradyrhizobium strains to further understand their phenotypic differences. Analyses were performed using bioinformatics approaches. We found IS elements disrupting and inserted at regulatory regions of genes involved in symbiosis. Further comparative analyses with 21 Bradyrhizobium genomes revealed insertional polymorphism with distinguishing patterns between B. diazoefficiens and B. japonicum lineages. Finally, 13 of these potentially impacted genes are differentially expressed under symbiotic conditions in B. diazoefficiens USDA 110. Thus, IS elements are associated with the diversity of Bradyrhizobium , possibly by providing mechanisms for natural variation of symbiotic effectiveness. [ABSTRACT FROM AUTHOR]

The research was conducted at Brawijaya University and West Nusa Tenggara, from March 2013 to October 2013. The tailings areas of the gold mine contains high mercury (Hg) as much as 1,090 ppm, and living microbes (resistance) exist in a small number in such a condition. Microbial P solvents encountered came from the genus Bacillus with a population of 23 x 103 cfu g-1 and N-fixing bacteria encountered are of the genus Bacillus, with a population of 4 x 103 cfu g-1. Identification of species using Becton Dickinson Phoenix test, both species belong to Bacillus megaterium and Bacillus pumilus. While the waste corn and peanuts that has been composted for 4 weeks acquired P-solubilizing bacteria, such as Enterobacter, Bacillus and Pseudomonas, and N-fixing bacteria found was Pseudomonas and Azotobacter. While testing the activity and antagonism of N-fixing and P-solubilizing bacteria, the result on agar media did not show antagonism in its growth. Bacillus pumilus and Bacillus megaterium effective at 5 % molasses medium with the number of 0.15 x 1012 on seven days of incubation.

Cd accumulation in crops has become a global environmental problem because it endangers human health. Screening for microorganisms that can reduce Cd accumulation in crops is a possible measure to address this issue. However, success has been limited, and most previous work did not involve bacteria. In the present study, a strain of N-fixing bacteria (Burkholderia spp.) that exhibits high levels of Cd tolerance was screened. The ability of this bacterium to reduce Cd in rapeseed was then assessed in sterile hydroponic and open soil culture systems. In the hydroponic system, the Burkholderia inoculum promoted Cd fixation in rapeseed roots and thus reduced Cd enrichment in aboveground edible tissues (leaves). The mechanisms were related to increased activity of pectin methylesterase in root cell walls, and the transformation of the chemical form of root Cd from "active" (NaCl-extracted) to "inert" (HCl-extracted and residual Cd) states. Additionally, Burkholderia accelerated plant growth, thus shortening the period in which the plant is available for Cd absorption. In the soil culture system, Burkholderia also reduced Cd enrichment in rapeseed leaves in the presence of other microorganisms. Thus, the bacterial strain shows potential for broad application for reducing the accumulation of Cd in crops. [Display omitted] • A nitrogen-fixing bacteria (GN6) that can reduce cadmium in rapeseed was identified. • GN6 promoted Cd retention in rapeseed roots and reduces its "active state" in the cytoplasm. • GN6 accelerated plant growth and shorten the time available for absorption of heavy metals. • GN6 could reduce enrichment of Cd in rapeseed in the presence of other microorganisms. • We validated the potential application of GN6 for remediation of Cd-contaminated farmlands. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the influence of an application of different rates of mineral fertilizers and their combination with associative N-fixing Klebsiella planticola and Enterobacter spp., and sampling period on the number of fungi in Cambisol and grain yield of maize. The investigation was conducted on Mladenovac experimental station and in the Laboratory of Institute of Soil Science, Belgrade, during 2006. Unfertilized soil was used as the control soil. Each of the studied variants was carried out in three replications. The effect of the studied fertilizers was determined three times during the maize growing season, the number of fungi being determined by indirect dilution method on Czapek nutritive medium. The results of the study showed that all fertilization variants studied influenced, more or less, fungal growth in the study soil. However, the applied high content of mineral nitrogen, phosphorus and potassium, as well as their combination with bacterial inoculants brought about the highest increase in the number of fungi during all studied vegetation periods of maize. The highest increase in the number of soil fungi was registered in the second sampling period. The highest increase in the grain yield of maize was obtained by combined application of microbial inoculants and high rates of mineral NPK fertilizers.

The aim of this study was to evaluate the spatial distribution of total petroleum hydrocarbons (TPH) in rhizoplane and non-rhizosphere of Leersia hexandra, known as Japanese grass, the effect of oil on the aerial biomass of L. hexandra, the population of plant growth-regulating bacteria, and microbial respiration in rhizosphere and non-rhizospheric soil. Samples of rhizosphere and soil were collected at 14 points across a surface of 2.3 ha, layer 1 (0-15-cm depth), layer 2 (15-30 cm), and layer 3 (30-70 cm), to measure TPH (mg kg). The spatial distribution of TPH defined four study zones (Z): Z1: 1393, Z2: 3455, Z3: 5574, and Z4: 7544. TPH were higher in underlying layers in the four zones. Zone 2 produced the largest amount of aerial biomass; oil induced hormesis in the grass, but inhibited it at doses ≥5574. For the rhizosphere of L. hexandra, it was cut with a sterilized knife, stimulated the population of N-fixing and phosphorus solubilizing, heterotrophic bacteria, as well as microbial respiration (day 1, 14, 21, 42, and 63 after incubation) in the four zones. The population of the three groups of bacteria was more stimulated by weathered oil in rhizosphere soil, compared to non-rhizosphere soil and with control treatment, suggesting that the rhizosphere system of L. hexandra has the potential to bioestimulate beneficial microbial activity in unpolluted and polluted areas compared to non-rhizosphere soil. We recommend the use of L. hexandra to recover soils degraded by weathered oil in farms located in the Mexican humid tropics. [ABSTRACT FROM AUTHOR]

Population dynamics of Azotobacter chroococcum has been studied in the rhizosphere of a sugarbeet hybrid inoculated with Azotobacter strains 5, 8 and 14. Simultaneously we examined the effects of four levels of nitrogen fertilization (non-fertilized control, 50, 100, 150 and 200 kg N/ha) and the applications of manure and harvest residues. Samples were taken three times in May, July and October. The experiment included inoculated and non-inoculated variants at all four levels of fertilization, in five replicates.

The presence and composition of soil microbial communities has been shown to have a large impact on plant-plant interactions and consequently plant diversity and composition. The goal of the present study was to evaluate impact of arbuscular mycorrhizal fungi (AMF) and nitrogen-fixing bacteria, which constitutes an essential link between the soil and the plant's roots. A greenhouse pot experiment was conducted to evaluate the feasibility of using selected microbes to improve Hieracium pilosella and Medicago sativa growth on Zn-Pb-rich site. Results of studies revealed that biomass, the dry mass of shoots and roots, increased significantly when plants were inoculated with mycorrhizal fungi and nitrogen-fixing bacteria. The addition of Azospirillum sp. and Nostoc edaphicum without mycorrhiza suppressed plant growth. Single bacterial inoculation alone does not have a positive effect on M. sativa growth, while co-inoculation with AMF improved plant growth. Plant vitality (expressed by the performance index) was improved by the addition of microbes. However, our results indicated that even dry heat sterilization of the substratum created imbalanced relationships between soil-plant and plants and associated microorganisms. The studies indicated that AMF and N-fixers can improve revegetation of heavy metal-rich industrial sites, if the selection of interacting symbionts is properly conducted. [ABSTRACT FROM AUTHOR]

In 2006, the influence of different rates of applied mineral fertilizers and their combinations with bacterial inoculants [nitrogen (N)–fixing Klebsiella planticola and Enterobacter spp.] on the number of microorganisms from the N cycle in a Cambisol and the yield of maize was evaluated in this study. The results obtained implied that high rates of mineral fertilizers brought about an increase in the number of fungi and a decrease in the number of Azotobacter spp., oligonitrophiles, ammonifiers, and nitrifiers in soil. Combined application of microbial inoculants and low rates of mineral fertilizers resulted in the greatest increase in the number of Azotobacter spp., oligonitrophiles, and ammonifiers in soil. The greatest number of soil nitrifiers, as well as the grain yield of maize studied, were determined in the variants where combinations of the microbial inoculants and low and high rates of mineral fertilizers were applied. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the influence of an application of different rates of mineral fertilizers and their combination with associative N-fixing Klebsiella planticola and Enterobacter spp., and sampling period on the number of fungi in Cambisol and grain yield of maize. The investigation was conducted on Mladenovac experimental station and in the Laboratory of Institute of Soil Science, Belgrade, during 2006. Unfertilized soil was used as the control soil. Each of the studied variants was carried out in three replications. The effect of the studied fertilizers was determined three times during the maize growing season, the number of fungi being determined by indirect dilution method on Czapek nutritive medium. The results of the study showed that all fertilization variants studied influenced, more or less, fungal growth in the study soil. However, the applied high content of mineral nitrogen, phosphorus and potassium, as well as their combination with bacterial inoculants brought about the highest increase in the number of fungi during all studied vegetation periods of maize. The highest increase in the number of soil fungi was registered in the second sampling period. The highest increase in the grain yield of maize was obtained by combined application of microbial inoculants and high rates of mineral NPK fertilizers. [ABSTRACT FROM AUTHOR]

Soil is an ecological system that shelters various and numerous microorganisms whose enzymes play a central role in soil metabolic activities. The studies conducted from 1996 to this day are summed up in 17 monographs and several hundreds of research papers and reports of national and international significance. A large proportion of these studies dealt with the monitoring of microbiological activity, i.e., population size and enzymatic activity as indicators of application of mineral fertilizers, cultivation practices and pesticides, presence of high contents of heavy metals, and soil disturbances such as compaction, etc. For more than two decades, studies were focused on the effects of N-fixing bacteria on the production and technological characteristics of field and vegetable crops. These theoretical and experimental studies have resulted in the development of several commercial microbiological preparations - patented biological fertilizers and technology of their production. Application of preparations containing Bradyrhizobium/Rhizobium nodular bacteria brings significant increases in grain quality and yield and plant biomass of soybeans, peas, string beans, dry beans and alfalfa. Azotobacter inoculation positively affects the production and technological characteristics of sugarbeet, corn, wheat and other agricultural crops. Microbiological preparations have good prospects because their application is ecologically and economically justified. Namely, it is necessary to further advance the scientific basis of current agriculture because the cost efficiency of mineral fertilization can be improved by combining or correcting the application of mineral fertilizers with microbiological preparations. [ABSTRACT FROM AUTHOR]

Vachellianilotica (L.) Willd. Ex Del. is a multipurpose leguminous tree that is common in grassland and savanna ecosystems in southern and eastern Africa. These ecosystem soils are reported to be acidic and nutrient-limited, specifically with regards to nitrogen (N) and phosphorus (P). The presence of this plant in these terrestrial ecosystems improves soil fertility benefiting the surrounding vegetation due to its ability to fix atmospheric N. This study seeks to understand the N-fixing bacteria symbiosis and physiological adaptations of V. nilotica in these acidic and nutrient-deficient KwaZulu-Natal soils. The soils used for this study were collected from the Ukulinga Grassland Nutrient Experiment located at the Ukulinga research farm of the University of KwaZulu-Natal, Pietermaritzburg, South Africa. Due to long-term soil nutrient addition treatments, these soils offered a diverse nutrient variation for better understanding the effects of acidity and nutrient variation on microbial symbiosis, plant nutrition, and biomass accumulation of V. nilotica. V. nilotica was able to maintain growth by relying on both atmospheric and soil-derived N across all treatments decreasing carbon (C) growth costs. There was an increased reliance on atmospheric-derived N of un-nodulated high N-treated plants. The plants grown in high N + P soils were able to nodulate with various species from the Mesorhizobium genus, which resulted in increased biomass compared to other plants. The results of this study show that V. nilotica can alter N sources to reduce C growth costs. In addition, both nodulating and free-living soil N2 fixing bacteria such as Caulobacter rhizosphaerae, Sphingomonas sp. and Burkholderia contaminans identified in the experimental soils may play an important role under P-deficient conditions. [ABSTRACT FROM AUTHOR]

Sustainable cropping systems rely on a minimum of external inputs. In these systems N is largely acquired in animal manures and leguminous green manures. Little is known of how these organic forms of N fertilizer influence the presence and activity of free-living N-fixing bacteria. High concentrations of inorganic N in soil inhibit N-fixation in cyanobacteria and Azotobacter spp. It is likely that manure and fertilizer applications would result in concentrations of inorganic N capable of inhibiting N fixation and, ultimately, the presence of these organisms. We investigated the effect of synthetic and organic N fertilizer sources on the populations and N-fixation potential of free-living N-fixing bacteria in the Farming Systems Trial at the Rodale Research Institute. Field plots received the following N treatments prior to corn ( Zea mays L.) production: (1) Legume rotations and green manures supplying about 165 kg N ha; (2) beef cattle manure applied at a rate of 220 kg N ha (plus 60 kg N ha from 1994 hay plow-down); or (3) fertilizer N (urea and NHNO) applied at a rate of 145 kg N ha. Soil samples were collected at two depths from corn plots four times during the growing season, and analyzed for soil moisture, soil pH, numbers of N-fixing cyanobacteria and Azotobacter spp., extractable NHand NO, and potentially mineralizable N. Soil samples collected in mid-July were analyzed for nitrogenase activity (by CH reduction) and total C and N. Populations of Azotobacter spp. and cyanobacteria were influenced only slightly by treatment; however, cyanobacteria species composition was notably influenced by treatment. Nitrogenase activity in surface soils was greatest in legume-N plots and in subsurface plots levels were greatest in fertilizer-N plots. Populations and activity of free-living N-fixing bacteria appeared to be somewhat reduced in all plots as a result of low soil pH levels and high concentrations of inorganic N across all treatments. Annual applications of N to all plots resulted in high levels of potentially mineralizable N that in turn may have reduced non-symbiotic N-fixation in all plots. [ABSTRACT FROM AUTHOR]

The rapid development of cities in the recent 10 years caused a reduction in the cultivated land area, which only accounts for 14% of the total land area in China. Land development and reclamation have been regarded as an effective way to compensate farmland occupation. However, most of the newly reclaimed land has poor soil fertility and suitability; in some cases, the production capacity is only 10–30% of the occupied farmland. In order to ameliorate the soil quality of the newly reclaimed land, this study evaluated the effects of commercial organic fertilizer (0.75, 1.50, and 2.25 kg/m2), mushroom residue (1.50, 2.25, and 3.00 kg/m2), biogas slurry (150, 225, and 300 kg/m2), vegetable cake (0.30 and 0.60 kg/m2), and chemical compound fertilizer (37.50 g/m2) on the pH, moisture content and organic matter content (OMC), available phosphate, total nitrogen, alkaline hydrolysis nitrogen, microbial biomass carbon and nitrogen, and number of total bacteria and phosphate-solubilizing bacteria, as well as the growth of maize seedlings. The results from this study indicate that the soil quality (OMC is an indicator) was ameliorated by chemical and organic fertilizers, in particular commercial organic fertilizers, which caused a 9.35–16.35% increase in moisture content, a 11.56–18.72% increase in pH, a 1.73–2.15 fold increase in OMC, a 338.44–491.41% increase in available P, a 36.80–48.14% increase in total N, a 95.32–128.34% increase in alkaline hydrolysis N, a 92.57–178.38% increase in total bacterial numbers, and a 7.57–20.87 fold increase in microbial biomass carbon compared with the control. The pot experiment further indicated that soil amended with commercial organic fertilizers caused a 20.35–30.55% increase in the height and a 12.50–16.67% increase in the total dry weight of maize seedlings. In addition, representative strains with the ability to dissolve phosphorus and fix nitrogen were successfully isolated using the culture method, and were then identified based on colony morphological observation and 16S rDNA sequence analysis, which help us to not only understand why organic fertilizer has great effect on soil improvement, but also provides beneficial microbial resources for further study. [ABSTRACT FROM AUTHOR]

Revegetation with native leguminous shrub Caragana microphylla in the Horqin Sandy Land, China, has been reported to increase plant coverage and diversity, and ameliorate abiotic soil property. However, comprehensive investigation of soil microbial-community composition after revegetation in this area has been rarely conducted. In this study, DNA of sand dunes restored for a period of 12 and 30 years, and an unrestored sand dune (control), was extracted and sequenced using Illumina Miseq. The results indicated that revegetation of C. microphylla significantly altered soil microbial communities as reflected by the significantly different bacterial and fungal composition and fungal diversity between the restored dunes and the control; however, there was no significant difference in soil microbial composition between the dunes restored for different years. Specifically, microbial consortia that involved in a wide range of ecological function, including recalcitrant organic carbon decomposition, plant-microbe symbiosis and nitrogen fixation, were enriched on restored dunes particularly on the 30-year restored dune. The changes in soil microbial communities were significantly correlated with the content of soil organic carbon (SOC) and the proportions of labile and recalcitrant organic carbon in SOC, which may indicate a mutual-regulated ecological improvement between soil abiotic and biotic processes along sand dune restoration. • 11058 & 2454 of bacterial & fungal OTUs, classified to 36 & 5 phyla, were defined. • Soil microbial assemblage on the restored dunes differed from unrestored sand dune. • More decomposer of recalcitrant organic C accumulated in topsoil of restored dunes. • Relative abundance of endophytes and N-fixing bacteria increased after restoration. • Soil microbial composition was shaped by changes in the content & fraction of SOC. [ABSTRACT FROM AUTHOR]