Soil Bacterial Populations Research Articles

Soil microbial activity, yield and grain quality of rice (Oryza sativa L.) as influenced by graded doses of fluoride in alfisols

A field experiment was conducted at Regional Research and Technology Transfer Station (RRTTS), Chiplima, OUAT, during 2014–15 and 2015–16 to study the impact of graded doses of fluoride on soil microbial activity, yield and grain quality of rice. Six doses of fluoride i.e., No fluoride, 100, 150, 200, 250 and 300 ppm F in form of hydrofluoric acid (HF) were applied as foliar spray. Highest grain (36.73 q/ha) and straw (47.34 q/ha) yield of rice was recorded with T1 (No fluoride) where as lowest grain (32.90 q/ha) and straw (40.09 q/ha) yield was observed with T6 (foliar spray of F @ 300 ppm as HF). The grain yield was decreased significantly with increasing doses of fluoride. The decrease in grain yield was highest (10.42%) with T 6 (foliar spray of F @ 300 ppm as HF) over control (T1 = No fluoride) where a lowest value of 3.02% was observed Significantly highest total chlorophyll content (4.53 mg/g fresh leaf) was observed with T 1 which was decreased to lowest value of 2.26 mg/g fresh leaf (T6) due to increasing doses of fluoride. The lowest value with respect to leaf area index (4.18), grain length (4.38 mm), kernel elongation (6.18 mm), plant height (123.78 cm) and panicle length (22.28 cm) was recorded with T6 (foliar spray of F @ 300 ppm as HF). Howeverhighest F uptake (24.71 kg/ha) was recorded with foliar spray of F @ 300 ppm as HF (T6). The variation in grain quality parameters such as protein content (R2=0.982), amylose content (R2=0.981) and alkali value (R2=0.839) were significant due to increase in F doses. Soil microbial biomass carbon (MBC), soil dehydrogenase activity (DHA) and soil bacterial population were decreased with increased doses of F irrespective of crop growth stages.

Investigation on the Association of Soil Microbial Populations with Ecological and Environmental Factors in the Pearl River Estuary

An investigation on the soil microbe populations from an agricultural inning area at the Pearl River estuary in Guangdong province, China was conducted via high through-put sequencing. The results revealed abundant diversity in the soil bacterial and fungal populations. In total, 197103 sequence tags were obtained from soil samples, most of which represented bacterial genera Actinomycetes, Bacillus and Marinobacter, while a majority of 118378 tags obtained were derived from fungal genera Clostridium, Devosia, Bradyrhizobium, Bdellovibrio, Phenylobacterium, Penicillium, and Emericella. Furthermore, nine physiological indexes (pH, available phosphorous, basic-group nitrogen, available potassium, catalase, sucrose, urease, phosphatase, and organic matters) were measured in three soil samples, and the association between these physiological indexes and microbe population composition was examined. The results revealed obvious inter-sample differences associated with ten dominating microbial groups: genera Clostridium, Devosia, Bradyrhizobium, Bdellovibrio, Phenylobacterium, and Penicillium were mainly impacted by pH (with a positive correlation), genera Sphingomonas and Acinetobacter mainly by available phosphorous (positive correlation), and genera Gemmatimonas and Pseudomonas by both pH and available phosphorous (negative correlation). Our study suggested that regulation of microbial species/populations might help improve soil environment to facilitate the growth of crops’ above-ground parts, and this provides practical information for inning agriculture.

EFFECT OF PHENACYLPYRIDINIUM SALTS ON BACTERIAL POPULATION IN LIGHT OLIVE-BROWN SOIL OF BUNDELKHAND REGION (U.P.) INDIA

Effect of phenacylpyridinium bromide (1a) and p-chlorophenacylpyridinium bromide (1b) was investigated on the soil bacterial population by plate dilution method. Based on the average total bacterial count at different concentrations of salts, it was observed that salt 1b was more bactericidal than salt 1a and deleterious effectivity increased with the increasing level. The greater antibacterial effect of salt 1b may probably be attributed to the presence of chlorine atom attached to benzene ring.

Strengthening detoxication impacts of Coprinus comatus on nickel and fluoranthene co-contaminated soil by bacterial inoculation

To develop an efficient and environmental-friendly approach to detoxicate nickel (Ni) and fluoranthene co-contaminated soil, the combined application of Coprinus comatus (C. comatus) with Serratia sp. FFC5 and/or Enterobacter sp. E2 was investigated. The pot experiment tested the influences of bacterial inoculation on the growth of C. comatus, content of Ni in C. comatus, Ni speciation in soil, fluoranthene dissipation, soil enzymatic activities, bacterial population and community structure. With the inoculation of bacteria, the fresh weights of C. comatus, concentration of Ni in C. comatus and the dissipation rates of fluoranthene were increased by 17.73–29.38%, 68.97–204.97% and 34.84–60.90%, respectively. Notably, results illustrated that the co-inoculation of FFC5 and E2 showed better effect in biomass enhancement, Ni accumulation and fluoranthene dissipation than solitary inoculation. Simultaneously, higher soil enzymatic and microbiological activities suggested that the integrated detoxication method of bacteria and C. comatus could improve soil quality. Therefore, we can infer that bacterial inoculation strengthened detoxication effect of C. comatus in Ni-fluoranthene co-contaminated soil, indicating that the combined application of C. comatus and bacteria can be an efficient alternative for detoxicating Ni and fluoranthene co-contaminated soil.

Plasmid-Mediated Bioaugmentation for the Bioremediation of Contaminated Soils

Bioaugmentation, or the inoculation of microorganisms (e.g., bacteria harboring the required catabolic genes) into soil to enhance the rate of contaminant degradation, has great potential for the bioremediation of soils contaminated with organic compounds. Regrettably, cell bioaugmentation frequently turns into an unsuccessful initiative, owing to the rapid decrease of bacterial viability and abundance after inoculation, as well as the limited dispersal of the inoculated bacteria in the soil matrix. Genes that encode the degradation of organic compounds are often located on plasmids and, consequently, they can be spread by horizontal gene transfer into well-established, ecologically competitive, indigenous bacterial populations. Plasmid-mediated bioaugmentation aims to stimulate the spread of contaminant degradation genes among indigenous soil bacteria by the introduction of plasmids, located in donor cells, harboring such genes. But the acquisition of plasmids by recipient cells can affect the host’s fitness, a crucial aspect for the success of plasmid-mediated bioaugmentation. Besides, environmental factors (e.g., soil moisture, temperature, organic matter content) can play important roles for the transfer efficiency of catabolic plasmids, the expression of horizontally acquired genes and, finally, the contaminant degradation activity. For plasmid-mediated bioaugmentation to be reproducible, much more research is needed for a better selection of donor bacterial strains and accompanying plasmids, together with an in-depth understanding of indigenous soil bacterial populations and the environmental conditions that affect plasmid acquisition and the expression and functioning of the catabolic genes of interest.

In-Situ Bioremediation of DDTs and PAH Contaminated Aging Farmland Soil Using Blood Meal

ABSTRACTThe use of blood meal was studied for in-site bioremediation of contaminated farmland soil. The combination of blood meal and indigenous microorganisms helped to in-site remediate the combined contaminated aging farmland soil of DDTs and PAH in Shenyang, China. The concentration of DDTs and PAHs was 47.94 ± 0.63 μg/kg and 690.10 ± 5.16 μg/kg, respectively. Biostimulation using blood meal or glucose promoted the bioremediation rate of DDTs and PAHs. Compared to glucose, blood meal was a longer term repair additive of DDTs and PAHs, and the remediation result was more efficient and durable. In the blood meal treatment, plowing the soil once every 7 days could increase the soil enzyme activities and bacterial populations, and it could significantly promote the remediation rates of DDTs (P < 0.05) and more evidently promote the remediation rates of PAHs. The DDTs and PAHs remediation rates increased from 32.18% and 20.17% to 43.41% and 26.09%, respectively, in soil treated with blood meal and plowed weekly after the five month remediation. This study provides an highly efficient in-site farmland soil bioremediation technology that could have practical utility.

Rice straw decomposition affects diversity and dynamics of soil fungal community, but not bacteria

Straw decomposition increased amounts of soil organic carbon and changed microbial biomass. But the different impacts of rice straw decomposition on the succession of bacterial and fungal community composition in field conditions were poorly understood. The objective of this study was to investigate the development of soil bacterial and fungal communities during rice straw decomposition in field conditions, and the relationship between soil chemical/physical properties and the evolution of microbial communities. A 1-year field study (90, 180, 270, and 360 days) was conducted, including the straw decomposition soil and control (no straw decomposition soil). The bulk soil samples (0–15-cm depths) from three replicate plots per treatment were collected for the analysis of soil properties and of microbial diversity parameters. Soil bacterial and fungal community structures and population sizes were determined by applying PCR-denaturing gradient gel electrophoresis (DGGE) and quantitative PCR (qPCR). The bacterial and fungal community diversity was evaluated using the following parameters: Shannon–Wiener diversity index, richness, and evenness. Moreover, the relationship between soil properties and the changes of microbial communities was analyzed using redundancy analysis (RDA). The results showed that, in contrast to bacteria, the soil fungal population size and diversity indices were significantly increased during different time points of rice straw decomposition, and reached to the highest value at 360 days. When compared with the bacterial DGGE profiles, the fungal DGGE profiles significantly changed between the straw decomposition soil and control, and the dominant soil fungal genera varied apparently. Bacterial 16S ribosomal RNA (rRNA) and fungal 18S rRNA gene sequences obtained from the main DGGE bands were further sequenced, among which Penicillium sp., Aspergillus sp., and Acremonium sp. have the ability to degrade cellulose. RDA suggested that the soil available P, organic C, pH, and bulk density were the main factors influencing the variation in the fungal community structures and diversities. The fungal community structures displayed distinct successions during rice straw decomposition. But such finding was not observed in bacterial communities. The ratio of fungi to bacteria measured by qPCR was higher in the straw decomposition soil compared with the findings in control, indicating that fungi predominated in straw decomposition. Especially, our study deduced that the diversified cellulolytic fungal genera highly enriched in rice straw decomposition soils had great potential of mining novel cellulose-decomposing enzymes.

Comparison of rhizosphere properties as affected by different Bt- and non-Bt-cotton (Gossypium hirsutum L.) genotypes and fertilization.

Incorporation of genetically modified crops in the cropping system raises the need for studying the effect of these crops on the soil ecosystem. The current study aimed to compare the effect of Bacillus thuringiensis (Bt)- and non-Bt-cotton (Gossypium hirsutum L.) genotypes on rhizosphere properties under fertilized and unfertilized soil conditions. One non-Bt-cotton (IUB 75) and four Bt-cotton varieties (IUB-222, MM-58, IUB-13, FH-142) were sown in a Randomized Complete Block Design (RCBD) in a factorial fashion with three replications under unfertilized (T1) and fertilized (T2 at NPK 310-170-110kgha-1) soil conditions. The culturable soil bacterial population was recorded at flowering, boll opening, and harvesting stages, while other rhizosphere biological and chemical properties were recorded at harvesting. Results revealed that Bt-cotton genotypes IUB-222 and FH-142 showed significantly higher rhizosphere total nitrogen, NH4+-N, available phosphorus, and available potassium. Total organic carbon and microbial biomass carbon was also maximum in the rhizosphere of IUB-222 under fertilized conditions. Similarly, bacterial population (CFU g-1) at flowering stage and at harvesting was significantly higher in the rhizosphere of IUB-222 as compared to non-Bt- (IUB-75) and other Bt-cotton genotypes under same growth conditions. It showed that Bt genotypes can help in maintaining soil macronutrients (total nitrogen, available phosphorus, and available potassium) under proper nutrient management. Moreover, Bt-cotton genotypes seem to strengthen certain biological properties of the soil, thus increasing the growth and yield capability, maintaining available nutrients in the soil as compared to non-Bt cotton, while no harmful effects of Bt cotton on soil properties was detected.

Glyphosate, 1,1’- dimethyl-4,4’-bipyridinium dichloride and Atrazine induces changes in Soil organic carbon, bacterial and fungal communities in a tropical alfisol

The increasing use of agrochemicals for weed control has raised concerns about their ecotoxicological effects on soil micro-biota communities and soil functions which serve as indicators of soil quality. Thus, this study was conducted to evaluate the effects of continuous field applied herbicides glyphosate, paraquat, atrazine and their combined forms over a period of five years on soil organic carbon, bacterial and fungal population in Akure, Ondo State Nigeria. Soil samples from farmer’s field which have been exposed to continuous herbicide application were collected and analysed for physio-chemical properties, organic carbon, total bacterial and fungal population. Simultaneously, soil samples designated as control were collected from adjacent fields with no history of herbicide application and analysed. Results showed a significant (P=0.05) 86% and 128% increase in bacterial population from glyphosate and atrazine treated fields respectively and 42% decrease in paraquat and Glyphosate + paraquat fields when compared with the untreated field. A significant 35% decrease in fungal population was observed in fields applied with atrazine and a further 10% decrease in fungal populations in all herbicide treated fields irrespective of herbicide type and combinations when compared with the untreated field. These changes also correlates with the abundance of beneficial microbes such as Pseudomonas aeruginosa, Pseudomonas fluorescens, Proteus mirabilis, Aspergillus flavius with a probable influence on plant growth promotion and potentials for biodegradation of persistent herbicides. SOC, SOM and pH was significantly (P=0.05) increased in atrazine and atrazine + paraquat treated fields when compared with the untreated fields and other herbicide treatments.

Diversity of Soil Microbial Communities from an Iron Mining Area (Oued Zem, Morocco)

Abstract Microbial communities in the soil were collected from 20 samples of an iron mining area (Ait Ammar, Oued Zem, Morocco), and unaffected samples were analysed to identify the effects of metal concentrations on functional diversity (Biolog® EcoPlates), and structural diversity (polymerase chain reaction-denaturing gradient gel electrophoresis of 16S rDNA). Aliivibrio fischeri is mainly used for evaluating polluted soil. The functional diversity was assessed by using such indices as area under substrate utilisation curve, richness, Shannon- Weaver and evenness indices. The analysis of similarities and the non-metric multidimensional scaling analyses of DGGE profiles showed that metals in the soil do not have a significant influence on bacteria. Principal component analysis of Biolog data revealed the similarity in the metabolic profiles of mining samples. These results suggest that the direction and the distance from the iron mine tailings do not have significant effects on the metabolic and structural diversity of the soil bacterial population. The toxicity of metals in soils heavily contaminated with Fe and P did not affect the quantities of microbial populations and did not significantly change the microbial diversity of contaminated soils.

Effect of Pesticides on Bacterial and Fungal Populations in Ecuadorian Tomato Cultivated Soils

Indiscriminate use of insecticides and fungicides leads to a combined contamination of pesticide residues in the soil environment and causes a severe threat to beneficial microbial activities. Hence, it is essential to assess the microbial populations of soils in the biosphere. In this study, two insecticides, cypermethrin and chlorpyrifos alone and in combination with two fungicides, mancozeb and carbendazim, were assessed for their effects on the bacterial and fungal populations in two tomato cultivated soils. Samples of soil-1 and soil-2 were collected from tomato cultivated fields of El Quienchi, Pichincha, Ecuador. Initially the physico-chemical characteristics of soils, e.g., soil pH, organic matter, total nitrogen, electrical conductivity, sand, silt and clay contents were detected, and then soil bacterial and fungal populations were determined. The influence of selected pesticides alone or in combination on the bacterial and fungal population was concentration-dependent; the populations were increased with increasing concentration of pesticides up to 5.0 kg ha−1 compared to the controls in 10-day incubated soils. The bacterial and fungal populations continued to increase up to 20 days, and then, gradually decreased after 30 and 40 days of incubation. The results clearly indicate that application of individual and/or mixtures of the pesticides in cultivation of tomato, at field application rates (2.5–5.0 kg ha−1), significantly improved the bacterial and fungal populations in soil-1 and soil-2. However, further increase in the dose of pesticides (7.5–10 kg ha−1) dramatically decreased the bacterial and fungal populations. On the other hand, insecticides in combination with fungicides showed negative effect on fungal populations.

Molecular Study of Indigenous Bacterial Community Composition on Exposure to Soil Arsenic Concentration Gradient.

Community structure of bacteria present in arsenic contaminated agricultural soil was studied with qPCR (quantitative PCR) and DGGE (Denaturing Gradient Gel Electrophoresis) as an indicator of extreme stresses. Copy number of six common bacterial taxa (Acidobacteria, Actinobacteria, α-, β- and γ-Proteobacteria, Firmicutes) was calculated using group specific primers of 16S rDNA. It revealed that soil contaminated with low concentration of arsenic was dominated by both Actinobacteria and Proteobacteria but a shift towards Proteobacteria was observed with increasing arsenic concentration, and number of Actinobacteria eventually decreases. PCA (Principle Component Analysis) plot of bacterial community composition indicated a distinct resemblance among high arsenic content samples, while low arsenic content samples remained separated from others. Cluster analysis of soil parameters identifies three clusters, each of them was related to the arsenic content. Further, cluster analysis of 16S rDNA based DGGE fingerprint markedly distributed the soil bacterial populations into low (< 10 ppm) and high (> 10 ppm) arsenic content subgroups. Following analysis of diversity indices shows significant variation in bacterial community structure. MDS (Multi Dimensional Scaling) plot revealed distinction in the distribution of each sample denoting variation in bacterial diversity. Phylogenetic sequence analysis of fragments excised from DGGE gel revealed the presence of γ-Proteobacteria group across the study sites. Collectively, our experiments indicated that gradient of arsenic contamination affected the shape of the soil bacterial population by significant structural shift.

Anaerobic soil disinfestation reduces survival and infectivity of Phytophthora nicotianae chlamydospores in pepper

Phytophthora nicotianae is the principal causal agent of root and crown rot disease of pepper plants in Extremadura (western Spain), a spring-summer crop in this region. Preplant soil treatment by anaerobic soil disinfestation (ASD) may effectively control plant pathogens in many crop production systems, but field conditions and availability of C sources can limit its practical application. A laboratory experiment was conducted to study P. nicotianae control by ASD with low temperatures and several carbon (C) sources: rice bran, rapeseed cake, grape pomace and brewer’s spent grain. Survival and infectivity of pepper by P. nicotianae chlamydospores were reduced with all C sources assayed and redox potential in all ASD treatments indicated that reductive soil conditions were achieved. Rice bran (20tonsha−1); rapeseed cake (20tonsha−1), and grape pomace (40tonsha−1) were also assayed in a field experiment in early spring. Survival and infectivity of P. nicotianae were also reduced with all C sources. An increase of dehydrogenase and urease activities and a strong pH decline were observed with rice bran and rapeseed cake, probably related to an increase of anaerobic bacterial populations in soil. Application of ASD with high C source rates may be effective in control of P. nicotianae under low temperature conditions.

Diazinon dissipation in pesticide-contaminated paddy soil: kinetic modeling and isolation of a degrading mixed bacterial culture.

Dissipation kinetics of diazinon was investigated in soils culled from a paddy field with a long history of the pesticide application. Goodness of fit statistical indices derived from several fitted mono- and bi-exponential kinetic models revealed a bi-phasic pattern of the diazinon dissipation curve at 15 and 150mgkg-1 spiking levels, which could be described best by the first-order double exponential decay (FODED) model. Parameters obtained from this model were able to describe the enhanced dissipation of diazinon as the result of repeated soil applications, where a larger fraction of the pesticide readily available in the solution phase was dissipated with a fast rate. Cluster and principal component analysis (PCA) of denaturing gradient gel electrophoresis (DGGE) obtained from soil bacterial populations revealed that they were only affected at the 150mgkg-1 diazinon concentration. This was also supported by the phylogenetic tree obtained from sequences of the main gel bands. Accordingly, bacterial populations belonging to Proteobacteria were enriched in the soil following three treatments with diazinon at 150mgkg-1. The Shannon's index revealed a nonsignificant increase (P≤0.05) in overall diversity of soil bacteria following diazinon application. Diazinon-degrading bacteria were isolated from the paddy soils in a mineral salt medium. Results showed that the isolated mixed culture was able to remove 90% of the pesticide at two concentrations of 50 and 100mgL-1 by 16.81 and 19.60days, respectively. Sequencing the DGGE bands confirmed the role of Betaproteobacteria as the main components of the isolated mixed culture in the degradation of diazinon.

Atmospheric Deposition-Carried Zn and Cd from a Zinc Smelter and Their Effects on Soil Microflora as Revealed by 16S rDNA.

In this study, we investigated the influence of heavy metals (HM) on total soil bacterial population and its diversity pattern from 10 km distance of a Zinc smelter in Feng County, Qinling Mountain, China. We characterized and identified the bacterial community in a HM polluted soil using 16S rDNA technology. Out results indicated that the maximum soil HM concentration and the minimum bacterial population were observed in S2 soil, whereas bacterial diversity raised with the sampling distance increased. The bacterial communities were dominated by the phyla Proteobacteria, Acidobacteria and Actinobacteria in cornfield soils, except Fimicutes phylum which dominated in hilly area soil. The soil CEC, humic acid (HA)/fulvic acid (FA) and microbial OTUs increased with the sampling distance increased. Shewanella, Halomonas and Escherichia genera were highly tolerant to HM stress in both cultivated and non-cultivated soil. Finally, we found a consistent correlation of bacterial diversity with total HM and SOM along the sampling distance surrounding the zinc smelter, which could provide a new insight into the bacterial community-assisted and phytoremediation of HM contaminated soils.

A Study on Soil Bacterial Population in Steel Company and Some Related Area in Erbil City in Relation to Heavy Metal Pollution

Present study was conducted to investigate the impact of heavy metal pollution from Erbil steel company on soil physicochemical properties and bacterial population of surrounding soils. The highest bulk density, pH and total organic carbon were 0.774±0.001, 9.31±0.032, 36.447±0.005 g.Kg -1 respectively were observed inside Erbil steel company. The concentrations of all the metals were higher within the steel company in comparison with the other sites and the maximum values were 292±0.577, 8.4±0.208, 259±0.577 and 7480±0.866 ppm for Pb, Cd, Cu and Zn respectively. The concentrations of Cd, Cu and Zn in Erbil steel company soil are exceeded the permissible limits for soil. The isolated bacterial genera in Erbil steel company soil were Acinetobacter , Bacillus , Micrococcus , Neisseria , Pseudomonas and Staphylococcus . These isolates are considered tolerant to alkaline pH and elevated levels of heavy metals from the steel company. Minimum Arthrobacter spp. (0.32×10 5 ), proteolytic bacteria (0.57×10 5 ) and asymbiotic nitrogen-fixers (0.12×10 5 ) cfu.g -1 dry soil were in the soil of steel company and minimum bacterial population was observed in Nawroz soil (0.05×10 7 ) cfu.g -1 dry soil followed by Erbil steel company soil (0.06×10 7 ) cfu.g -1 dry soil. The relationships between the heavy metals and the microbial populations were negative. The correlations among: pH, total organic C, Cu, Pb and Zn were significantly positive.

Seasonal and Temporal Dynamics of Physicochemical and Biological Properties of Chronosequence Coal Mine Spoil Soils

Open cast coal mining cause severe damage to soil physicochemical and biological properties. The present study, therefore, was carried out to evaluate the effect of open cast coal mining on the seasonal and temporal dynamics of soil properties. Soil samples were collected from chronosequence spoil soils and one undisturbed forest in two seasons for 2 consecutive years. Most of the studied soil properties deviated from the forest soil. The dumping soils were highly acidic as compared to the forest soil. Soil acidity decreased with increase in soil age. Significant negative correlation of soil pH and nickel (Ni), zinc (Zn), copper (Cu), nitrogen (N), phosphorus (P) (p &lt; 0.01), indicated that increase in spoil soil acidity increased the solubility/availability of these heavy metals, while decrease in soil acidity increased the availability of N and P. High soil acidity and higher concentration of heavy metals reduced the bacterial population number and activity of soil enzymes. Soil enzymes and bacterial population number significantly correlated with each other indicating their interdependence. Seasonal dynamics was observed in soil temperature. While, temporal dynamics was exhibited by soil pH, N, P, Ni, Zn, Cu, and dehydrogenase activity. Soil moisture content, arsenic, bacterial population number, urease, and phosphatase activity exhibited both seasonal and temporal dynamics. Ordination diagram of principal component analysis showed strong relationship of soil biological properties with undisturbed forest and heavy metals with disturbed spoil soils.

Low Effective Surface Area Explains Slow Oxidation of Co‐Granulated Elemental Sulfur

Core Ideas The oxidation of co‐granulated elemental S (ES) was slower than that of powdered ES. Bacterial abundance and community composition in the soil localized around a granular fertilizer (diammonium phosphate [DAP] + ES [10%]) differed from that in the soil with powdered DAP + ES (thoroughly mixed). Differences in bacterial abundance and community composition could not explain the differences in the percentage of ES oxidized between co‐granulated and powdered ES. The reduction in effective available surface area of ES particles corresponded to the slower oxidation of co‐granulated ES compared to powdered ES. Elemental S (ES) is commonly used as a S fertilizer but must be oxidized to sulfate for plant uptake. Oxidation of ES in co‐granulated fertilizers has been shown to be slower than that of powdered ES mixed with soil. We hypothesized that the slow oxidation is due to limited access of S oxidizers to the interior of the granule. To test this hypothesis, an experiment was conducted to compare chemical properties and bacterial populations in soil in the vicinity of a granule (diammonium phosphate [DAP] + ES [10%]) and in soil mixed with powdered DAP + ES. Copy numbers of 16S ribosomal ribonucleic acid (rRNA) genes and of a functional gene soxB were quantified to indicate the abundance of total and S‐oxidizing bacteria, respectively, and the total bacterial community composition was analyzed by terminal restriction fragment length polymorphism (TRFLP). After 20 wk of incubation, 42% of the co‐granulated ES was oxidized compared to 95% for the powdered ES. The soil pH dropped by 1.0 and 1.7 units for the granular and powdered treatments, respectively. We observed significant changes in bacterial abundance and community composition during incubation. However, none of the alterations in chemical properties and bacterial populations could explain the adverse effects of granulation on ES oxidation. The difference in ES oxidation rate between the co‐granulated and powdered ES corresponded to the difference in surface area of the granule and of the individual ES particles, quantitatively corroborating that the available surface area exposed to S‐oxidizing microorganisms is the limiting factor for co‐granulated ES oxidation.

Linking the Physicochemical Properties with the Abundance and Diversity of Rhizospheric Bacterial Population Inhabiting Paddy Soil Based on a Concerted Multivariate Analysis of PCR-DGGE and RISA

ABSTRACTTo unravel the existence of dominant bacterial population in the paddy fields of Eastern Uttar Pradesh, India and their relation to the prevailing soil physicochemistry using multivariate statistical analyses, a cumulative culture-independent 16S rRNA based Polymerase chain reaction-Denaturing gradient gel electrophoresis (PCR-DGGE) and a 16S-23S ribosomal intergenic spacer analysis (RISA) have been performed. Detrended correspondence analysis (DCA) and principal component analysis (PCA) biplot analyses were used to assess the relation between soil bacterial population and its physicochemistry. DCA analysis exhibited a strong dependence of bacterial existence on the soil physicochemical variables, such as organic matter, total nitrogen, inorganic nutrients, temperatures, and moisture status. Soil dehydrogenase activity (DHA) was assessed to check the metabolic activity of all soil samples which showed a range of 0.012–0.050 nmol TPF g−1 min−1 with significant variation (p < 0.01). Out of 96 bands excised, 45 different phylotypes were obtained using both techniques which elucidated the abundance of Cyanobacteria over other soil bacterial population. Scytonema sp., Leptolyngbya sp. and different uncultured cyanobacterial species were the major genera found. Profiling data obtained through PCR-DGGE and RISA were used in alpha diversity and rarefaction curve analysis suggested site 6 (Chandauli) as the most diversity rich site. Thus extensive dataset of weighted and unweighted variables generated through DGGE and RISA coupled with metabolic functioning of soil and multivariate analyses provided an excellent opportunity to map the soil microbial structure in paddy fields and their regulation with existing soil environment.

Effect of Continuous Monocropping of Tomato on Soil Microorganism and Microbial Biomass Carbon

ABSTRACTSoil microorganisms play an important role in recycling and transformation of nutrients. Soil microbiological parameters and microbial biomass carbon (MBC) have been suggested as possible indicators of soil quality. Soil microorganisms and MBC in different continuous cropping soils were investigated. Results showed that bacterial population was the highest, followed by actinomycetes, and fungi were the lowest at 0–30 cm soil depth. The amount of soil microorganisms decreased with increasing soil depth (0–10 > 10–20 > 20–30 cm). Soil microbial ratios at different depths proved to be responsive to time (year) variations in continuous monocropping tomato, except those at 0–10 to 10–20 cm depth for fungi and 10–20 to 20–30 cm depth for bacteria. Soil MBC for 12 years of continuous cropping was significantly lower than those for 5, 8, and 10 years (P < 0.05). Continuous cropping years, soil depth, and the interaction of these two parameters significantly influenced soil fungal, bacterial, and actinomycetes populations and MBC. Bacterial population at the 0–10 cm soil layer was a sensitive indicator of continuous cropping of tomato. Soil fungal count increased with increasing monocropping time within 5–8 years.