Studies on the rhizosphere microflora of yellow birch seedlings

Summary The rhizosphere microflora of yellow birch seedlings grown in a forest soil in tanks in the greenhouse has been investigated. In general it was found that the rhizosphere effect of yellow birch roots in the A horizon was lower than that observed with cropped plants; nevertheless a stimulation of microbial development was obtained. Of the micro-organisms studied, bacteria, and ammonifying and methylene-blue-reducing organisms appeared to be predominant types in the root zone. Counts were, on the whole, lowest when plants broke dormancy and began to increase in the later periods of growth. There was no appreciable difference between control and rhizosphere soils in regard to incidence of specific nutritional types of bacteria. Analysis of the rhizosphere population of roots growing in the B horizon showed a distinctly greater rhizosphere effect than that obtained in the A horizon. The data suggest that the rhizosphere effect in the latter was obscured because of its high organic-matter content and its abundant and active microflora.Contribution No. 481     

Development of rhizosphere and rhizoplane microflora of Aristida coerulescens in the Libyan desert

Summary Microflora of rhizosphere soil, rhizoplane and macerated root-portions of Aristida coerulescens, naturally occurring in the Libyan desert, were different in count and isolates, in the different root zones. A rhizosphere effect characteristic of each zone is shown. The root base contained the lowest numbers of microflora (bacteria and fungi) whilst the root tip included the highest counts. Distribution of most of the individual fungal species in the different root zones and root-surfaces is given in text.     

Investigations into rhizosphere microflora

Summary Effect of light and dark treatments on rhizosphere and rhizoplane microflora of two crops,viz Triticum aestivum. Linn. andHordeum vulgare Linn. has been investigated. Higher microbial population was recorded from the rhizosphere of plants exposed to continuous light while continuous dark set harboured lesser microflora. The microflora in 12 hours alternate light and dark set exhibited an intermediate condition. Amino acids (both qualitatively and quantitatively) in root extracts were the least in continuous dark and the maximum in continuous light set. The variation in root leakage, physiological and morphological condition of the plants was thought to be the cause for change in microbial activity. A part of the Ph. D. thesis approved by University of Gorakhpur, Gorakhpur, India (1969).     

Effect of thiram on plant growth and rhizosphere microflora of barley and nodulation in cowpea

Summary Thiram applied as a seed dresser fungicide had no inhibitory effect on seedling height and rhizosphere microflora of barley plants (Hordeum vulgare) and on nodulation of cowpea plants (Vigna catjang).     

The rhizosphere microflora of wheat grown under controlled conditions II. Influence of the stage of growth of the plant,soil fertility and leaf treatment with urea on the rhizosphere soil microflora

Summary The rhizosphere effect of seminal roots of seedlings and of nodal roots of tillering plants of spring wheat ‘Kaspar’ was investigated under controlled conditions. The total number of micro-organisms recorded in the rhizosphere soil were significantly higher than for the non-rooted soil when investigated with the soil dilution plate method, but lower when fluorescence microscopy was used. Additions of inorganic fertilizer (NPK) decreased their numbers especially in rhizosphere soil of seminal roots and in non-rhizosphere soil, but did not change the ratio between bacteria and actinomycetes (B/A). In the rhizosphere soil the B/A ratio was higher than in the non-rhizosphere soil. An effect of urea leaf treatment was found with the dilution-plate method only in the rhizosphere soil of nodal roots, 3 to 7 days after the first treatment. Increased numbers of actinomycetes were found in this period in NPK fertilized soil, whereas increased numbers of bacteria were found at both fertility levels.     

Degradation of seed mucilage by soil microflora promotes early seedling growth of a desert sand dune plant

In contrast to the extensive understanding of seed mucilage biosynthesis, much less is known about how mucilage is biodegraded and what role it plays in the soil where seeds germinate. We studied seed mucilage biodegradation by a natural microbial community. High‐performance anion‐exchange chromatography (HPAEC) was used to determine monosaccharide composition in achene mucilage of Artemisia sphaerocephala. Mucilage degradation by the soil microbial community from natural habitats was examined by monosaccharide utilization tests using Biolog plates, chemical assays and phospholipid fatty acid (PLFA) analysis. Glucose (29.4%), mannose (20.3%) and arabinose (19.5%) were found to be the main components of achene mucilage. The mucilage was biodegraded to CO₂ and soluble sugars, and an increase in soil microbial biomass was observed during biodegradation. Fluorescence microscopy showed the presence of mucilage (or its derivatives) in seedling tissues after growth with fluorescein isothiocyanate (FITC)‐labelled mucilage. The biodegradation also promoted early seedling growth in barren sand dunes, which was associated with a large soil microbial community that supplies substances promoting seedling establishment. We conclude that biodegradation of seed mucilage can play an ecologically important role in the life cycles of plants especially in harsh desert environments to which A. sphaerocephala is well‐adapted.     

Engineering the plant rhizosphere

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Improvements in the physical properties of soil under the influence of the rhizosphere microflora of four different plant species

Summary Finger millet or locally known asragi (Eleusine coracana Gaertn.), sorghum (Sorghum vulgare Pers.), greengram (Phaseolus aureus Roxb.) and soybean (Glycine max L.) plants were raised on sterilized, sterilized and reinoculated with soil microflora and unsterile sandy loam soil in pots for 45 days. Qualitative studies on the edaphosphere microflora indicated the continuation of rhizosphere effect beyond the root surface (rhizosphere) region. Increased microbial population in the sterilized soil was attributed to the effect of sterilization in favour of faster establishment of added microorganisms. In general, steam sterilization had detrimental effects, whereas crop growth had beneficial effects on the soil physical properties. Ragi and greengram were found superior to sorghum and soybean in improving soil structure as evidenced by increased aggregate stability and hydraulic conductivity and decreased dispersion. Soil aggregates of less than 2.00 mm size were found to be increased due to crop growth. The rhizosphere microflora in association with roots of the growing plants is suggested to play a pivotal role in improving soil structure.     

Studies in polysaccharide production and growth of Azotobactervinelandii MTCC 2459, a plant rhizosphere isolate

Azotobacter vinelandii MTCC 2459, a novel exopolysaccharide (EPS) producer, was isolated from Nelumbium nelumbo (lotus) stem. The EPS produced has a sugar composition different from the existing industrial gums (glucose, galactose and rhamnose). Optimization of the basal medium composition and other physical parameters (viz. pH, temperature, time, etc.) are reported in this paper. A final yield of 16·5% of the amount of the carbon source supplied was obtained in shake flask cultures, indicating the potential of the organism for production of useful EPS on a large (industrial) scale.     

Effect of some sulphur compounds on soil microflora of spruce rhizosphere

The effect of a long-term application of sulphite, thiosulphate and sodium sulphate on the soil microflora and spruce seedlings was investigated in a pot experiment. Sulphur compounds decreased the concentration of bacteria, including thiobacilli, increased the concentration of microscopic fungi and sulphate-reducing bacteria; they inhibited respiration, nitrification and oxidation of thiosulphate, stimulated ammonification and oxidation of elemental sulphur. In certain cases the spruce rhizosphere exhibited just the opposite effect. In the rhizosphere the sulphate-reducing bacteria were suppressed together with thiobacilli, whose unit oxidative activity increased substantially. Growth of seedlings was inhibited by sulphite and stimulated by thiosulphate and sulphate. Sulphite, the effects of which were similar to those of sulphur dioxide immissions, was the most effective compound. In regions influenced by immissions the soil is apparently intoxicated by the absorbed sulphite.     

放线菌制剂对人参生长及根域土壤微生物区系的影响

以小兴安岭地区人参为研究对象,探索放线菌制剂对人参的促生效应及对人参根区、根表土壤微生物区系的影响.结果表明： 经放线菌制剂Streptomyces pactum（Act12）处理后,人参药用部分产量增加,品质改善;叶片诱导酶活性提高,根系活力增强;土壤中细菌、放线菌的数量和比例显著增加,真菌的数量和比例减少.与对照相比,土壤微生物区系结构改变:优势菌荧光假单胞菌、韩国假单胞菌和氧化微杆菌在根区、根表土壤中的数量大幅提高;病原真菌烟色织孢霉在根区土壤中减少,在根表土壤中消失.表明施用放线菌制剂Act12能够改善土壤微生物区系,提高人参植株的抗性和根系活力,增加产量并改善品质.     

烟草根际微生物研究

利用选择性培养基,对土壤肥力肥沃、中等、贫瘠的烟区根际细菌、真菌和放线菌进行了分离和测数。根据菌体形态及培养特征、生理生化指标及16S rDNA部分序列分析等,对根际自生固氮菌、磷细菌、钾细菌进行了鉴定和分类。主要结果为：土壤肥沃的烟区根际细菌的数量最多,土壤贫瘠的烟区数量最少;土壤贫瘠烟区根际真菌的数量较多,中等和肥沃烟区的较少;根际故线菌的数量随土壤肥力的降低而依次减小。从不同肥力烟区分离的根际自生固氮菌、磷细菌、钾细菌以革兰氏阴性杆菌为主,分别属于10个属。土壤的肥沃程度对根际3类细菌的种类和数量都有影响,总体上看,土壤肥沃和中等的条件下,细菌类群的多样性和丰富度较大,而贫瘠土壤细菌类群的优势度较大。     

Effect of aflatoxin-contaminated groundnut cake on rhizosphere microflora of some vegetable plants

Plant and Soil - Amendment of groundut cake stimulated bacterial and fungal populations in rhizospheres of Rumex, okra, and clusterbean. Maximum rhizosphere effect was noticed when the plants were...     

Studies on the rhizosphere mycoflora of broad bean and cotton. Effect of fungal filtrate on plant growth

The dominating rhizosphere fungi of broad bean (Vicia faba Linn.) variety “Giza 1”, and cotton (Gossypium barbadense Linn.) variety “Giza 47”, were grown in liquid medium. After 10 days, filtrates were obtained and sterilized by filtration through sintered-glass filter. Plants were grown in sterile sand which was supplemented with nutrient solution. Every plant was irrigated with fungal filtrate, unconsumed medium, and water. The filtrates of the rhizosphere fungi of both broad bean and cotton stimulated plant growth.