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.     

Studies on the rhizosphere microflora of a desert plant

The response of the bacterial population to edaphic drought of the Egyptian desert was investigated. The influence of the rhizosphere on the microbial population as compared with soil apart was studied. The total microbial flora, total simple nutritional microflora, spores of simple and complex nutritional requirements, Actinomycetes and Fungi were estimated. Some groups of organisms which carry out certain important biochemical processes in the soil were also investigated, namely, cellulose decomposers, nitrifiers, Azotobacter and Clostridia. It was found that significatnly higher donsities of microbial population existed in the rhizosphere than in soil apart. This was attributed to organic matter and root secretion furnished by the growing roots of the desert plant, in addition to the presence of relatively moister conditions around the root than in soil apart. The high densities of microflora present in the rhizosphere indicate that the desert soil of this locality is suitable for reclamation since the only limiting factor in the proliferation of soil microorganisms are soil organic matter and moisture. Cellulose decomposers and nitrogen fixers, were found in high densities in the rhizosphere but not detected in the soil apart. The significance of the rhizosphere as constituting a microhabitat is discussed. The probable contribution of the periotrophic mantle of bacteria for protecting root cells against edaphic drought is also noted. Mineralization of the high microbial protein in the rhizosphere supplies the plant with the necessary nutrients.

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Изучение микрофлоры ризосферы растений в пустыне

Изучалась реакция популяций бактерий на засуху в египетской пустыне. Исследовалось влияние ризосферы (по сравнению со свободной почвой) на популяцию микробов. Было определено общее количество микроорганизмов, количество микроорганизмов со скромными требованиями к питанию, количество спорообразующих микроорганизмов е простыми и комплексными требованиями к питанию и количество актиномицетов и грибов. Изучались также некоторые группы микроорганизмов, осуществляющих важные биологические превращения в почве, а именно микроорганизмов, разлагающих целлюлозу, нитрификаторов, Azotobacter и Clostridia. Было установлено, что в ризосфере микробы гораздо более многочисленны, чем в свободной почве. Кроме стносительно большей влажности среды вблизи корней это обусловливается и влиянием органического вещества и корневых выделений, попадающих в почву пустыни. Обильная микрофлора в ризосфере растений в прстине свидетельствует о том, что почва пустыни в исследуемых местах пригодна для обработки, так как лимитирующими факторами в развитии микроорганизмов являются только влажность и органическое вещество почвы.

     

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.     

The rhizosphere microflora of wheat grown under controlled conditions I. The effect of soil fertility and urea leaf treatment on the rhizoplane microflora

Summary Microbial colonization of seminal roots of seedlings and of nodal roots of tillering plants was studied on spring wheat ‘Kaspar’ cultivated in growth, chambers. Methods were developed to microbially condition the soil before seeding and to regulate soil humidity. Addition of inorganic nutrients (NPK) to the soil increased the number of rhizoplane bacteria and actinomycetes, but did not effect the number of fungi on seminal and nodal roots. Urea leaf treatments stimulated bacteria and actinomycetes 7 and 9 days after treatment. Fourteen days after urea leaf treatment, however, bacterial numbers were mostly reduced, especially on seminal roots, while numbers of actinomycetes generally equalled the control. Root types and soil fertility did not obviously interact with the effect of urea leaf treatment on rhizoplane bacteria and actinomycetes. The only effect of urea on total numbers of fungi, was a reduction of their numbers on seminal roots 9 days after treatment at both NPK-levels.     

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).     

Survival of Bacillus subtilis AF 1 in the bacterized peanut rhizosphere and its influence on native microflora and seedling growth

A mutant of Bacillus subtilis AF 1 (an antifungal strain with plant growth-promoting activity, resistant to 100 g streptomycin/ml) was isolated from pigeon pea rhizosphere and, when used in peanut bacterization, decreased fungal and bacterial numbers and increased the actinomycete population in the rhizosphere. Over 28 days, AF 1 declined by 0.9 log c.f.u. in sterilized soil and by 2.6 log c.f.u. in native soil. From the seedlings raised with peanut seeds bacterized with AF 1 at 6.5 log c.f.u./seed, 4.1 and 4.7 log c.f.u. of AF 1 were recovered from the rhizosphere and total underground parts, respectively. Bacterization with AF 1 had no significant growth-promoting or -inhibiting effect on the peanut.     

Metabolic quotient of the soil microflora in relation to plant succession

Summary In this study we propose the hypothesis that ecosystem succession is accompanied by a decrease in the metabolic quotient qCO₂ (respiration-to-biomass ratio) of the soil microflora. The qCO₂ is calculated from basal respiration (CO₂-C·h^-1) per unit microbial biomass carbon (C_mier). The hypothesis was tested by studying two primary successions on recessional moraines of the Rotmoos Ferner (Austria) and the Athabasca Glacier (Canada). For both soil seres (0->200 years) it was shown that the qCO₂ decreased with time, which corroborated the hypothesis. In addition, the short term development of the qCO₂ was demonstrated with a revegetation trial. We observed a rise in qCO₂ for the first two years after reclamation, followed by a subsequent decrease.     

Effects of organic amendments to soil on the rhizosphere microflora of antirrhinum infected withVerticillium dahliae Kleb.

Summary Organic (e.g. chitin, green manure, cellulose) amendments to soil induced quantitative and qualitative changes in the rhizosphere microflora of antirrhinum plants infected withVerticillium dahliae Kleb. Whereas reduction in disease severity occurred with chitin and green manure amendments, an increase in disease severity was observed with the application of cellulose. The reduction of the disease severity with chitin and green manure may be correlated with the increased population of actinomycetes in the antirrhinum rhizosphere.     

Some effects of diazinon on the microflora of submerged soils

Summary The application of diazinon, an organophosphorus insecticide, at the rate of 2 kg and 20 kg active ingredient per hectare to submerged Maahas clay significantly stimulated the actinomycete population. A distinct zone of brown pigmentation formed in that part of the profile commonly referred to as the oxidized layer. A profuse growth of actinomycetes developed from the soil samples of this pigmented zone when streaked onto the nutrient agar. A visible increase in algal populations was noted in the standing water of the diazinon-treated soil.     

Respiration and microflora of the rhizosphere soil of wheat influenced by foliar application of urea

The numbers of micromycetes and bacteria were investigated with respect to oxygen consumption in the rhizosphere soil of wheat and in non-rhizosphere soil. Plants after foliar application of urea (2 % solution) and non-treated plants were cultivated in degraded chernozem and garden soil in a green-house. Changes in oxygen consumption by the suspensions of rhizosphere and non-rhizosphere soils corresponded to changes in the number of bacteria designated as the rhizosphere effect (R/S). Values of R/S depended on the presence of organic substrates. Changes in oxygen consumption by the soil suspension from the rhizosphere of wheat occurring due to foliar application of urea corresponded to changes in the amount of microflora. The results obtained are discussed with respect to a possible utilization of the data to follow metabolic activity of soils in a natural environment (in situ) determined according to oxygen consumption by a soil suspension, and to assess changes in the microflora of rhizosphere and non-rhizosphere soil.     

The rhizosphere microbiome and plant health

The diversity of microbes associated with plant roots is enormous, in the order of tens of thousands of species. This complex plant-associated microbial community, also referred to as the second genome of the plant, is crucial for plant health. Recent advances in plant-microbe interactions research revealed that plants are able to shape their rhizosphere microbiome, as evidenced by the fact that different plant species host specific microbial communities when grown on the same soil. In this review, we discuss evidence that upon pathogen or insect attack, plants are able to recruit protective microorganisms, and enhance microbial activity to suppress pathogens in the rhizosphere. A comprehensive understanding of the mechanisms that govern selection and activity of microbial communities by plant roots will provide new opportunities to increase crop production.     

Methane dosage to soil and its effect on plant growth

Two protocols for following soil methane enrichment were used, one with methane dosed as a carbon source ([C]-soil) and one with methane plus minerals ([C+M]-soil). Methane oxidation occurred much faster in soil receiving minerals in addition to methane than in the control soil receiving only methane. In both treatments, only a small fraction of methane (2% to 14%) was converted into microbial biomass C. Nevertheless, a strong increase in soil microbial biomass (up to 1.5 to 2.0-fold) was achieved in the [C+M]-soil in a 3-week period. Due to methane application, the NO₃ ^- content of the soil was significantly decreased, by 83% to 90% in the [C]-soil and by 56% to 83% in the [C+M]-soil. Soil enzymatic activities were slightly increased in the [C+M]-soil only. The soil-methane incubation did not alter the composition of the monitored microbial populations in the soil or in rhizosphere of plants. In the [C]-soil, methane incubation resulted in reduction of the shoot dry wt of maize by 8% to 12%. In the [C+M]-soil under non-limiting mineral-nutrient status, a significant increase in shoot dry wt was observed for maize (13%), a neutral effect was registered for spinach and a negative effect was observed for wheat.     

Physiological study on the influence of some plant oils in rats exposed to a sublethal concentration of diazinon

The present study was aimed to evaluate the influence of olive, sesame and black seed oils on levels of some physiological parameters in male rats exposed to diazinon (DZN). Body weight changes, and levels of serum total protein, albumin, glucose, triglycerides, cholesterol, high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), very low density lipoprotein cholesterol (VLDL-C), atherogenic index (AI), atherogenic coefficient (AC), cardiac risk ratio (CRR), glutathione (GSH), superoxide dismutase (SOD) and malondialdehyde (MAD) were selected as physiological parameters. The experimental animals were distributed into nine groups. Rats group exposed to DZN and fed with normal diet resulted in pronounced severe changes including reduced body weight gain rate, significantly increase in levels of serum albumin, glucose, cholesterol, LDL-C, AI, AC, CRR and MDA while levels of HDL-C, GSH and SOD were decreased. In rats treated with DZN, the supplementation of the olive, sesame and black seed oils showed remarkable lowering influences of physiological alterations. Moreover, the present results confirmed that these oils possess antioxidative effects against DZN toxicity. Finally, the present findings suggest that these oils are safe and promising agents for the treatment of physiological disturbances induced by DZN and may be also by other pollutants, and toxic and pathogenic factors.     

The distribution of topically applied heavy metals in the soil

Summary Long-term pot experiments were conducted to determine the leaching potential of topically applied lead, cadmium, and nickel through the soil. Four rates of each metal (0, 10, 100 and 200 mg/kg soil), in the nitrate form were used. Metals were extracted with acidic ammonium acetate after 30 weeks of intermittent leaching. The concentration of extractable element varied with the depth in the soil and the type of extractable metal. Lead was confined to the upper few centimeters of soil whereas cadmium moved down to a considerable depth. Nickel was more uniformly distributed over the total soil depth than the other two metals. The concentration gradients observed are discussed with respect to their effect on germination and yield of plants.