Non-rhizosphere Soil Samples Research Articles

Analyzing the Efficacy of Phosphate Solubilizing Microorganisms by Enrichment Culture Techniques

Phosphate solubilizing microorganisms (PSMs) were isolated from rhizoplane, rhizosphere and non-rhizosphere of different leguminous plants. To isolate efficient phosphate solubilizers the rhizosphere and non-rhizosphere soil samples were enriched with different phosphate sources like tricalcium and rock phosphate. PSMs were detected in all the regions, but their number gradually decreased from rhizosphere, rhizoplane and non-rhizosphere soil. When compared to fungal population, bacterial population was more in number. Tephrosia purpurea recorded the highest bacterial population of 30.15 × 106 cfu/g, 50.51 × 106 cfu/g and 21.10 × 106 cfu/g in the rhizoplane, rhizosphere and non-rhizosphere regions respectively. In enrichment culture technique, highest phosphate solubilizing bacterial population was recorded in the rhizosphere soil of Clitoria ternatea (23 × 103 cfu/g) in tricalcium phosphate containing Pikovskaya’s (PVK) medium. In a plate assay method solubilization zone diameter produced by microorganisms was varied from 0.2 cm to 1.0 cm. The phosphate solubilization ability of the isolated microorganisms in a liquid PVK medium varied from 11.85 mg to 61.96 mg P2O5. The medium turned acidic during the incubation period. The pH varied among the organisms from the initial 6.5 to the final 3.2 during 15 days of incubation. Citric acid, fumaric acid, gluconic acid, glutaric acid, glyoxalic acid, ketobutyric acid, ketoglutaric acid, malic acid, malonic acid, succinic acid and tartaric acid are produced by the isolated PSMs. Seed or soil inoculation with phosphate solubilizing bacteria (PSB) is known to improve solubilization of fixed and applied phosphates in soil bring about higher crop yield. The PSM are effective as biofertilizers in enhancing crop yields in phosphate deficient soils. They are environmentally friendly and supply phosphate to plants in a sustainable manner.

Influence of the Number of Pathogen Causing Banana Fusarium Wilt and Soil Factors on the Infection Degree of Banana Plants

Banana fusarium wilt is one of the soil-borne diseases of seriously threat to banana production in the world. However, there is no effective method for prevention. The objective was providing theoretical basis for field diagnosis of banana fusarium wilt. Thirty rhizosphere and non-rhizosphere soil samples were collected from three typical banana plots (Jianfeng, Shiyuetian, Chongpo) infected by banana fusarium wilt. Applying dilution plate method to estimate the pathogenic number, fourteen soil physicochemical properties and nutrient concentrations were chemically determined. Results showed that pathogenic number and nutrient concentrations in rhizosphere soil were higher than non-rhizosphere soil, the pathogenic number and pH in rhizosphere soils significantly increased with increasing of plant infection grades, while the concentrations of available P and B decreased with increasing of plant infection grades. It was concluded that infection degree of banana plants was mainly determined by pathogenic number, pH and the concentrations of available P and B.

Soil Microbial Functional Diversity from Different Infection Grades of Banana Fusarium Wilt (<i>Fusarium oxysporum</i> f. sp. Cubense)

Thirty rhizosphere and non-rhizosphere soil samples from different infection grades(0, I, III, V and VII) of three typical banana plots(Jianfeng, Shiyuetian, Chongpo) infected by banana fusarium wilt (Fusarium oxysporum f. sp. cubense) in Hainan province were collected to study the microbial community functional diversity applying Biolog-ECO microplates technology. The results are as follows: (1) Overall carbon source metabolic capacities of soil microbial community weaken with increasing of infection grades of banana fusarium wilt. (2) Richness indices, Simpson indices, Shannon indices and McIntosh indices of soil microbial community gradually decreased with increasing of infection grades of banana fusarium wilt. (3) Principal component analysis show that metabolic characteristics of soil microbial community significantly change between the healthy plants and diseased plants in the same banana plot. The results would provide information for explaining the pathogenesis of banana fusarium wilt and controlling its incidence by applying microbial ecology to regulate soil environmental measures.

Comparison of Soil Bacterial Communities of Pinus patula of Nilgiris, Western Ghats with Other Biogeographically Distant Pine Forest Clone Libraries

The bacterial community structure of the rhizosphere and non-rhizosphere soil of Pinus patula, found in the Nilgiris region of Western Ghats, was studied by constructing 16S rRNA gene clone libraries. In the rhizosphere and non-rhizosphere soil clone libraries constructed, 13 and 15 bacterial phyla were identified, respectively. The clone libraries showed the predominance of members of culturally underrepresented phyla like Acidobacteria and Verrucomicrobia. The Alphaproteobacteria and Acidobacteria clones were predominant in rhizosphere and non-rhizosphere soil samples, respectively. In rhizosphere, amongst Alphaproteobacteria members, Bradyrhizobium formed the significant proportion, whereas in non-rhizosphere, members of subdivision-6 of phylum Acidobacteria were abundant. The diversity analysis of P. patula soil libraries showed that the phylotypes (16S rRNA gene similarity cutoff, ≥97 %) of Acidobacteria and Bacteroidetes were relatively predominant and diverse followed by Alphaproteobacteria and Verrucomicrobia. The diversity indices estimated higher richness and abundance of bacteria in P. patula soil clone libraries than the pine forest clone libraries retrieved from previous studies. The tools like principal co-ordinate analysis and Jackknife cluster analysis, which were under UniFrac analysis indicated that variations in soil bacterial communities were attributed to their respective geographical locations due to the phylogenetic divergence amongst the clone libraries. Overall, the P. patula rhizosphere and non-rhizosphere clone libraries were found significantly unique in composition, evenly distributed and highly rich in phylotypes, amongst the biogeographically distant clone libraries. It was finally hypothesised that the phylogenetic divergence amongst the bacterial phylotypes and natural selection plays a pivotal role in the variations of bacterial communities across the geographical distance.

Rhizosphere phosphorus depletion by three crops differing in their phosphorus critical levels

AbstractIt has been reported for many soils that maize (Zea mays L.) has a higher soil‐P critical level than soybean (Glycine max L.) and sunflower (Helianthus annuus L). The objective of this work was to compare the rhizosphere P depletion in these three species in order to investigate if they differ in their capacity to acquire soil P. Sequential P fractionation and pH were determined in rhizosphere and nonrhizosphere soil samples from field and greenhouse experiments. Neither sunflower (the species with highest rhizosphere acidification) nor soybean or maize showed a significant relationship between P depletion and rhizosphere pH. The labile P fraction and the NaOH‐Pi fraction had lower values in the rhizosphere than in the bulk soil in 38% and 77% of the studied cases, respectively. Sunflower and especially maize presented a more intense Pi depletion than soybean. The comparison between sunflower and maize revealed that neither of them took a clear advantage over the other in terms of P depletion. Rhizosphere Pi depletion was associated with the amount of P acquired by the plants. We conclude that the accessibility to different P pools does not explain the differences in soil‐P critical levels among the three species.

General microflora, arbuscular mycorrhizal colonization and occurrence of endophytes in the rhizosphere of two age groups of Ginkgo biloba L.of Indian Central Himalaya

The populations of the general microflora (bacteria, actinomycetes and fungi) in the rhizosphere and their corresponding non-rhizosphere soil samples of Ginkgo biloba L. of two age groups (Group A, <25 years-young trees; Group B, >60 years-old trees) growing under a temperate location of Indian Himalayan Region (IHR) have been determined. Observations were also made for the diversity, distribution and colonization of arbuscular mycorrhizal (AM) fungi and occurrence of endophytes in roots of G. biloba. The population of general microflora was found to be higher in the rhizosphere of Group B trees, more clearly reflected in terms of rhizosphere: soil (R:S) ratios. Contrary to this, per cent colonization and spore densities of AM fungi were higher in the rhizosphere of Group A trees as compared to the rhizosphere of Group B. AM fungal colonization was observed mostly in form of loose coils. All the spores detected, belonged to the genus Glomus with five different types. Presence of endophytes (both bacteria and fungi) was observed in the cortical cells of G. biloba roots, more profound in case of Group B trees. Data suggest that, while the species of Glomus dominated the rhizosphere of G. biloba, an inverse correlation exist between the colonization of general microflora and the colonization of AM fungi including endophytes.

Atividade microbiana em solo cultivado com cana-de-açúcar após aplicação de herbicidas

Objetivou-se neste trabalho avaliar os efeitos dos herbicidas na atividade respiratória da microbiota, na biomassa microbiana e no quociente metabólico em solo cultivado com plantas de cana-de-açúcar. Utilizou-se o delineamento inteiramente casualizado, no esquema de parcelas subdivididas, com quatro repetições. Nas parcelas, avaliou-se o efeito dos herbicidas e, nas subparcelas, o efeito do tempo após a aplicação destes. Os herbicidas utilizados foram: 2,4-D (1,30 kg ha-1), ametryn (1,00 kg ha-1), trifloxysulfuron-sodium (0,0225 kg ha-1) e a mistura ametryn+trifloxysulfuron-sodium (1,463+0,0375 kg ha-1, respectivamente). Realizou-se a aspersão dos herbicidas aos 60 dias após a brotação das gemas do material propagativo. Aos 15, 30, 45 e 60 dias após a aplicação dos herbicidas, amostras de solos rizosférico e não-rizosférico foram coletadas e analisadas quanto às seguintes características: taxa respiratória (TR), carbono da biomassa microbiana (CBM), quociente metabólico (qCO2) e acúmulo total de C-CO2 evoluído do solo (ATC). O ametryn aplicado isolado ou em mistura com trifloxysulfuron-sodium propiciou maiores TRs, ao passo que o 2,4-D apresentou pouca influência nessa variável. Maiores acúmulos de C-CO2 aos 60 dias após a aplicação dos herbicidas foram verificados nos tratamentos com trifloxysulfuron-sodium, ametryn e na mistura de ambos os produtos. A BM do solo foi reduzida na presença do ametryn isolado ou em mistura. Esses tratamentos resultaram em maiores valores de qCO2 aos 45 e 60 dias da aplicação.

Ação de herbicidas sobre microrganismos solubilizadores de fosfato inorgânico em solo rizosférico de cana-de-açúcar

Objetivou-se avaliar, com este trabalho, o impacto dos herbicidas ametryn e trifloxysulfuron-sodium, isolados ou em mistura, e 2,4-D na atividade dos microrganismos solubilizadores de fosfato inorgânico e a densidade populacional de bactérias e fungos do solo rizosférico de cana-de-açúcar. Plantas de cana-de-açúcar com três a quatro folhas completamente expandidas foram aspergidas com soluções de 2,4-D, ametryn, trifloxysulfuron-sodium e ametryn+trifloxysulfuron-sodium nas doses de 1,30; 1,00; 0,0225; e 1,463+0,0375 kg ha-1, respectivamente. Utilizou-se o delineamento inteiramente casualizado no esquema de parcelas subdivididas, com quatro repetições. Nas parcelas foram avaliados os efeitos dos herbicidas e, nas subparcelas, o efeito tempo após a aplicação dos herbicidas. Aos 15, 30, 45 e 60 dias após a aplicação (DAA), amostras de solos rizosférico e não-rizosférico foram coletadas e, em seguida, analisadas estimando-se a densidade populacional de bactérias e fungos, a atividade potencial de solubilização de fosfato inorgânico e a solubilização relativa de fosfato inorgânico. O 2,4-D reduziu a densidade populacional bacteriana do solo em todas as épocas de avaliação, demonstrando a maior sensibilidade desse grupo de organismos a esse composto. Todos os herbicidas provocaram redução na densidade populacional fúngica do solo somente aos 15 DAA. O trifloxysulfuron-sodium e o 2,4-D favoreceram as maiores atividades de solubilização de fosfato inorgânico aos 15, 30 e 45 DAA e aos 15 e 30 DAA, respectivamente, sem, no entanto, afetar a biomassa microbiana do solo. Maior solubilização relativa de fosfato inorgânico foi observada em amostras de solos tratados com a mistura ametryn+trifloxysulfuron-sodium, indicando alterações no sistema solo. Este trabalho evidenciou que a aplicação dos herbicidas na parte aérea de plantas de cana-de-açúcar afetou o número de microrganismos e a atividade de solubilização de fosfato na rizosfera.

Influence of grass species and soil type on rhizosphere microbial community structure in grassland soils

A number of studies have reported species specific selection of microbial communities in the rhizosphere by plants. It is hypothesised that plants influence microbial community structure in the rhizosphere through rhizodeposition. We examined to what extent the structure of bacterial and fungal communities in the rhizosphere of grasses is determined by the plant species and different soil types. Three grass species were planted in soil from one site, to identify plant-specific influences on rhizosphere microbial communities. To quantify the soil-specific effects on rhizosphere microbial community structure, we planted one grass species ( Lolium perenne L.) into soils from three contrasting sites. Rhizosphere, non-rhizosphere (bulk) and control (non-planted) soil samples were collected at regular intervals, to examine the temporal changes in soil microbial communities. Rhizosphere soil samples were collected from both root bases and root tips, to investigate root associated spatial influences. Both fungal and bacterial communities were analysed by terminal restriction fragment length polymorphism (TRFLP). Both bacterial and fungal communities were influenced by the plant growth but there was no evidence for plant species selection of the soil microbial communities in the rhizosphere of the different grass species. For both fungal and bacterial communities, the major determinant of community structure in rhizospheres was soil type. This observation was confirmed by cloning and sequencing analysis of bacterial communities. In control soils, bacterial composition was dominated by Firmicutes and Actinobacteria but in the rhizosphere samples, the majority of bacteria belonged to Proteobacteria and Acidobacteria. Bacterial community compositions of rhizosphere soils from different plants were similar, indicating only a weak influence of plant species on rhizosphere microbial community structure.

Isolation and characterization of agar-degrading Paenibacillus spp. associated with the rhizosphere of spinach.

Agar-degrading bacteria in spinach plant roots cultivated in five soils were screened, and four strains of Paenibacillus sp. were isolated from roots cultivated in three soils. The agar-degrading bacteria accounted for 1.3% to 2.5% of the total bacteria on the roots. In contrast, no agar-degrading colony was detected in any soil (non-rhizosphere soil samples) by the plate dilution method, and thus these agar-degrading bacteria may specifically inhabit plant roots. All isolates produced extracellular agarase, and could grow using agar in the culture medium as the sole carbon source. Zymogram analyses of agarase showed that all four isolates extracellularly secreted multiple agarases (75-160 kDa). In addition, the isolates degraded not only agar but also various plant polysaccharides, i.e., cellulose, pectin, starch, and xylan.

Functional diversity and community structure of microorganisms in rhizosphere and non-rhizosphere Canadian arctic soils

Functional diversities of microorganisms in arctic soil samples at three incubation temperatures were assessed using sole-carbon-source-utilization (SCSU). Soil samples from four sites were collected from the rhizosphere and non-rhizosphere soils. Microorganisms were extracted from samples and inoculated into ECO-Biolog plates and incubated at 4, 10 and 28 °C. Calculations of Shannon–Weaver diversity and Shannon–Weaver evenness were based on the substrate utilization in the Biolog plates. Shannon–Weaver diversities (H′) in rhizosphere samples were significantly greater ( \(\overline x\)H′ = 3.023 ± 0.197; P < 0.005) than in non-rhizosphere samples (\(\overline x\)H′ = 2.770 ± 0.154). Similarly, the evenness (E) of the inoculated microbial cells exhibited significant differences (P < 0.005) between the rhizosphere and non-rhizosphere soil samples (\(\overline x\)E = 0.880 ± 0.057 for soils with rhizosphere; \(\overline x\)E = 0.807 ± 0.044 for non-rhizosphere samples). Higher microbial diversity and evenness were observed in samples incubated at 4 °C than at 28 °C [least significant difference (lsd) = 0.29], and evenness indices were higher in rhizosphere samples than in non-rhizosphere soils incubated at all three temperatures (lsd = 0.02). Principal component analysis (PCA) of the multivariate data set differentiated the soil samples on the relatively gross scale of microbial communities isolated from rhizosphere and non-rhizosphere soils at all three temperatures.

Activity of protease extracted from rice-rhizosphere soils under double cropping of rice and wheat

Abstract Protease-active extracts were prepared from 2 rice-rhizosphere and non-rhizosphere soil samples 3 proteolytic isolates from the soil samples which were taken from water logged paddy fields (Gray Lowland Soils) under double cropping of rice and wheat that had been treated with chemical fertilizer (CF) or organic manure (OM). The activities were assayed and characterized using an artificial substrate, benzyloxycarbonyl-L-phenylalanyl-L-tyrosyl-L-leucine (ZFTL). The protease-active extracts from the rhizosphere and non-rhizosphere of the CF and OM soils (abbreviated as CFR, CFN, OMR, and OMN) showed an optimum pH between 7 and 8. The extracts hydrolyzed ZFTL to Tyr-Leu and Leu; generally, Tyr-Leu was the main reaction product. Activities of all the samples were inhibited by EDTA and p-chloromercuribenzoic acid (PCMB) but not by pepstatin and phenylmethanesulfonyl fluoride (PMSF). These results indicate that the main components of the ZFTL-hydrolases in CFR, CFN, 0MR, and OMN were essentially similar. Optimum pH for the activity of the protease extracted from a Gram negative rod (MNB003)., two actinomycetous isolates (MNA014., MRA017) was about 8, 8, and 8.5, respectively. Extract from the culture of MNB003 hydrolyzed ZFTL to Tyr-Leu., Leu,., the protease activity was inhibited by EDTA., PCMB. Protease activities of the extracts from cultures of the two actinomycetes were inhibited by EDTA but not by PCMB. The extract from culture of MNA014 produced mainly Tyr-Leu from ZFTL while MRA017 produced Leu. Characteristics of the protease activity from cultures of MNB003., MNA014 were similar to those of the enzyme extracted from a paddy field soil under single cropping (Takeuchi., Hayano 1994: Soil Sci. Plant Nutr., 40, 691-695) and from an Andosol under tomato cultivation (Hayano et al. 1987: Biol. Fertil. Soils, 4, 179-183), respectively.

Exposing Loblolly Pine Seedlings to Acid Precipitation and Ozone: Effects on Soil Rhizosphere Chemistry

AbstractRhizosphere and nonrhizosphere soils were sampled in association with the roots of field‐grown, 1‐year‐old loblolly pine (Pinus taeda L.) that had been exposed to simulated acidic precipitation and O3 treatments. Soil samples adjacent to roots and from the bulk soil were analyzed separately for H, Al3, Ca2, and Mg2 concentrations. For the acid precipitation treatment, H levels were significantly greater in the rhizophere compared with the bulk soil, but no clear trend could be attributed to acidic precipitation levels. Hydrogen ion concentrations associated with the O3 levels, at times, differed significantly by treatment, butnot between rhizosphere and bulk soil. Rain pH and 3 level produced no statistically significant distinction between rhizosphere and nonrhizosphere soil for Al3, Ca2, or Mg2. However, after combining rhizosphere and nonrhizosphere soil samples, Al3 concentrations were found to generally increase as rain pH decreased, whereas Ca2 and Mg2 followed the opposite pattern. No such pattern for O3 level was apparent. Significant interactions between acid precipitation and O3 treatments were not detected.

Rhodanese activity of flooded and nonflooded soils

Rhodanese activity (RA) was studied in 4 soils, incubated under flooded and nonflooded (60% water-holding capacity) conditions. RA in 3 soils including an acid sulphate soil pokkali increased 2.5–6.0-fold (over respective nonflooded soils), while activity of the enzyme decreased markedly in flooded alluvial soil. Similarly, anaerobic incubation of nonflooded soils under N 2 decreased RA in an alluvial soil, but increased it in pokkali soil. RA was negligible in soils, that had been reduced by flooding for 30 days and then sterilized by autoclaving. Rice rhizosphere soil exhibited significantly higher RA than the nonrhizosphere soil samples under flooded or nonflooded conditions. RA in aerobic soils was related to the microbial oxidation of S° to SO 2− 4. But, no relationship could be established between RA and S-oxidation in flooded soils and in rhizosphere soil suspensions of flooded rice plants.

Distribution and Abundance of Azotobacter in Wheat Fields of Bangladesh

The distribution and abundance of Azotobacter as well as heterotrophic bacteria in root, rhizosphere soil and non-rhizosphere soil samples from various wheat fields of four different areas under three districts were investigated in this study. The potential for nitrogen-fixation of five Azotobacter isolates was also detected. All samples tested were positive in their capacity to harbouring Azotobacter with a range of 26-100%. The population of heterotrophic bacteria ranged from 2.1 x 107 to 1.2 x 108 cfu/g sample. Ranges of total number of Azotobacter in different samples were 5.2 x 104 to 7.2 x 104 cfu/g, 17.2 x 104 to 25.5 x 104 cfu/g, and 12.4 x 104 to 16.7 x 104 cfu/g respectively for root, rhizosphere soil and non-rhizosphere soil. A positive correlation was found in Azotobacter colonization between root and rhizosphere, but it was negative in case of the population between heterotrophic bacteria and Azotobacter in rhizosphere. The highest amount of N was found to be fixed by the isolate M1 and the lowest by the isolate M4 and it was respectively 9.26 and 5.45 mg N/g substrate. In terms of the capacity to fix nitrogen in laboratory condition the five isolates of Azotobacter could be arranged as M1&gt; M3 &gt; M5 &gt; M4 &gt; M2. Keywords: Azotobacter, Wheat field, Nitrogen fixing potentialDOI: http://dx.doi.org/10.3329/bjm.v24i2.1262

Quantitative study of fungi in the rhizosphere.

Working with dwarf bean plants, the authors studied changes in the lengths of fungal mycelium in rhizosphere and non-rhizosphere soil at different stages of plant growth, using the soil-agar film technique. In general it appears that the stimulation of microbial growth in the rhizosphere was slight in the early stages of plant growth; the length of mycelium in rhizosphere soil increased with increase in vegetative growth of the plants, and decreased markedly at senescence of the plants.Respirometric studies on rhizosphere and non-rhizosphere soil samples indicated greater activity in rhizosphere soil. The degree of stimulation of activity in rhizosphere soil varied according to the stage of plant growth, with maximum activity corresponding to the stage of maximum vegetative growth of the plants.

Soil bacteria: comparisons of rhizosphere and nonrhizosphere populations.

Four sets, each of 100 bacterial isolates, were derived from two different flax rhizosphere and corresponding control (nonrhizosphere soil) samples. A two-stage principal component analysis was used to compare the nature and properties of these bacterial cultures which were selected by a random sampling method from primary isolation plates. These 400 experimental isolates were characterized by their reaction to a set of 98 tests. Principal component analysis was applied separately to the data for each of the four sets of cultures. The sets were then compared both in terms of the leading discriminating tests and of the detailed properties of the clusters of isolates detected. Because these isolates and a set of 100 named cultures (previously studied) were subjected to the same tests, the properties of groups of isolates from different sets could be directly compared. The kinds of isolates predominant in the rhizosphere samples were not represented amongst isolates derived from the corresponding control soil populations. The specific kinds of amino-acid-requiring isolates present in the control soil populations were not found in the corresponding rhizosphere populations. The two control soil sets of isolates (predominantly arthrobacter–coryneform-like organisms) were generally similar in their reactions to the tests used, but the two sets of rhizosphere isolates (predominantly pseudomonas-like organisms) were relatively dissimilar. The named species studied previously were not sufficiently indicative of the diversity found in the experimental isolates: this was especially true of the arthrobacter-like isolates. The numerical analyses yielded useful groupings of tests and of cultures and aided in their evaluation.