Effect of certain chemical fertilizers on the rhizosphere mycoflora ofOryza sativa linn

The present paper deals with the study of the effect of potassium fertilizer (Potassium sulphate) on rhizosphere mycoflora ofOryza sativa. The fertilization improves the microbial activity both in rhizosphere and nonrhizosphere regions. 40 lbs/acre dose of the fertilizer proved best for paddy growth and rhizosphere fungal poulation. The highest fungal population was recorded at the time of flowering of the plants.     

The effect of a nitrification inhibitor on the concentration of nitrate in grass during growth

Summary In an experiment on clay-loam soil ammonium sulphate with or without the nitrification inhibitor 2-chloro-6-(trichloromethyl) pyridine (at 2% of the weight of N in fertilizer) or sodium nitrate were applied at 100 or 200 lb N/acre to the seedbed before sowing S22 Italian ryegrass and again after the first cut. Eighty-four days after the first dressing, all the grass given 100 lb N/acre contained similar amounts of nitrate-N; with 200 lb N/acre, grass given ammonium sulphate alone contained most nitrate-N and grass given ammonium sulphate plus inhibitor least. Forty-two days after the second dressing, all the grass given 100 lb N/acre again contained similar amounts of nitrate-N and with 200 lb N/acre, grass given sodium nitrate contained most nitrate-N and that given ammonium sulphate plus inhibitor least.     

The effect of nitrate-nitrogen supply on bacteria and bacterial-feeding fauna in the rhizosphere of different grass species

Summary Microbial growth in the rhizosphere is affected by the release of organic material from roots, so differences in carbon budgets between plants may affect their rhizosphere biology. This was tested by sampling populations of bacteria and bacteriophagous fauna from the rhizosphere of Lolium perenne, Festuca arundinacea, Poa annua, and Poa pratensis, under conditions of high and low nitrate availability. Concentrations of soluble phenolics and lignin varied considerably between the species but were not related to differences in rhizosphere biology. L. perenne and F. arundinacea supported fewer bacteria than the Poa species. There was no significant rhizosphere effect on the groups of protozoa. The major indicators of rhizosphere productivity were the bacterial-feeding nematodes (mainly Acrobeloides spp.), and there was a large positive effect of added nitrate. Nematode biomass was significantly lower in the rhizosphere of the slow-growing P. pratensis compared with the fast-growing P. annua, indicating that the differential allocation of carbon has affects on rhizosphere biology. A large rhizosphere effect on enchytraeid worms was also observed, and their potential importance in the rhizosphere is discussed.     

Nitrate reduction in the leaves and numbers of nitrifiers in the rhizosphere ofPlantago lanceolata growing in two contrasting sites

Summary Numbers of autotrophic nitrifiers in the rhizosphere, and thein vivo nitrate reductase activity (NRA) in the leaves of individual plants ofPlantago lanceolata were determined in plants at two contrasting sites. In a dune grassland, high numbers of nitrifiers were present in the rhizosphere, and significant NRA was detected in the leaves. During dry periods nitrate utilization sometimes was depressed. In a wet hayfield, on peat soil, very low numbers of nitrifiers were found in the rhizosphere. Also the NRA was low. In the wet habitat, the NRA in the leaves of some fen species, containing aerenchyma in the roots, was higher than that ofP. lanceolata, not containing aerenchyma.Grassland Species Research Group. Publication No. 105.     

Comparison of the chemical changes in the rhizosphere of the nickel hyperaccumulator Alyssum murale with the non-accumulator Raphanus sativus

Changes in pH and redox potential were studied in the rhizosphere soil of a nickel hyperaccumulator plant (Alyssum murale) and of a crop plant, radish (Raphanus sativus). Differences in rhizosphere pH and reducing activity were found between the lateral and the main roots of both species, but the pH changes in the rhizosphere were similar in both species. Changes in pH were associated with the relative uptakes of cations and anions; whether the concentrations of heavy metals in the growth medium did not have any effect on the rhizosphere pH. The source of nitrogen (ammonium or nitrate) was the major factor determining the pH of the rhizosphere of both species. The redox potential of the rhizosphere was influenced by both the N-source and the concentrations of heavy metals. When heavy metals were not present in the growth medium, and nitrate was the N-source, the reducing capacity of A. murale roots was enhanced. However, the reducing activity of A. murale was always smaller than that of radish. Therefore, the mechanism of metal solubilization by the hyperaccumulator plant does not involve either the reduction of pH in the rhizosphere or the release of reductants from roots. The acidification and reducing activity of the roots of A. murale was always smaller than that of R. sativus.     

A rapid method for obtaining readily soluble phosphates and phosphate fixation in soils

Summary Following well known methods for the preparation of reagents for the determination of phosphates by the coeruleo-molybdate reaction, the preparation of a new series of colour standards is detailed.The procedure for estimating phosphate by a rapid technique is given and discussed, important points being ratio of extracting solution to soil, time of reaction and temperature of reaction. The development of the blue colour is otherwise carried out in the recognised manner.After the extraction of phosphates from the soil, the amount fixed from a phosphate solution in the presence of the same extracting solution by a further sample of the soil of the same weight is next determined, using the same technique. From these two results, the readily soluble phosphate in the soil and the fixation rate are arrived at.Tentative ranges and symbols are given for readily soluble phosphate in lbs per acre, and also for the fixation rate in lbs per acre.Publication authorised by the Director.     

Investigations on the role ofSuaeda fruticosa Forsk in the reclamation of saline and alkaline soils in West Pakistan plains

Summary Investigations onSuaeda fruticosa show that it can bring about reclamation of saline and alkaline soils in certain parts of West Pakistan Plains by collecting non-saline blown soil of sandy loam type and by absorbing large quantities of salts from the top soil. An estimate shows that more than 2,400 lbs of salts can be removed from one acre by a single harvest of the aerial parts in the fall each year. The dunes help in reclamation by diluting the salt concentration and decreasing the salt-holding capacity of the topsoil by changing the texture. It is estimated that by this method saline soils can be reclaimed within three years in southern and central parts of West Pakistan Plains which are frequented by dust storms.     

Nitrate production in the rhizosphere of Plantago species

Summary The production of nitrate in an old established dune grassland soil and its uptake by plants was studied by comparing amounts of mineral nitrogen and numbers of nitrifying bacteria in the rhizosphere on the one hand, and on the other accumulated nitrate and levels of nitrate reductase (NaR) of individual plants of three Plantago species,i. e., P. major, P. lanceolata andP. coronopus. For these three Plantago species andP. media basal levels of NaR in the absence of nitrate were determined in plants grown in culture solutions. The basal NaR levels ofP. major andP. media (species occurring on nutrient-rich soils) were significantly higher than those ofP. lanceolata andP. coronopus (species found on nutrient-poor soils). NaR activity increased in the presence of nitrate and was suppressed by ammonium.From the numbers of nitrifying bacteria in the rhizosphere and NaR activity in the leaves it was concluded that nitrate was produced in the root environments of the three Plantago species and that the compound was taken up by the plants. NaR activities and numbers of nitrifying bacteria were higher for individuals ofP. major than for those ofP. lanceolata andP. coronopus. No correlation was found between the ammonium levels and the numbers of nitrifying bacteria in the soil, and no indications of inhibition of nitrifying bacteria in the rhizosphere were obtained. For individuals ofP. lanceolata a correlation was found between the numbers of nitrifying bacteria in the soil and NaR activity in the leaves. The results are discussed in relation to the ecological habitats of the three species.Grassland Species Research Group Publication No.38.     

Root biomass distribution in a moist tropical montane forest

Effects of N sources (ammonium, nitrate and ammonitrate) and VA mycorrhizae (Glomus intraradices) on rhizosphere soil characteristics (pH, exchangeable acidity, exchangeable cations, inorganic N concentrations) growth and nutrient acquisition of coffee seedlings (Coffea arabica L. cv guatemala) were investigated in a pot study with an acid soil (Red Bluff Loam) sterilized by autoclaving. Ammonium addition decreased rhizosphere pH while nitrate and ammonitrate additions both increased rhizosphere pH. Mycorrhizae induced a higher pH, a lower exchangeable acidity and higher values of exchangeable cations in the rhizosphere. Ammonium addition resulted in a lower mycorrhizal infection than the two other N sources. Mycorrhizal plants grew better and accumulated more N, Ca and Mg than non-mycorrhizal plants.     

Nitrate respiration in Pseudomonas stutzeri A15 and its involvement in rice and wheat root colonization

Unlike most bacteria, the nitrogen-fixing rice-associated Pseudomonas stutzeri A15 disposes of three different nitrate reductases that enable conversion of nitrate to nitrite through three physiologically distinct processes, called nitrate assimilation, nitrate respiration and nitrate dissimilation. To study the role of nitrate respiration in rhizosphere fitness, a Pseudomonas stutzeri narG mutant was constructed and characterized by assessing its growth characteristics and whole-cell nitrate reductase activity in different oxygen tensions. Unexpectedly, the Pseudomonas stutzeri A15 narG mutant appeared to be a better root colonizer, outcompeting the wild type strain in a wheat and rice hydroponic system.     

Upscaling from Rhizosphere to Whole Root System: Modelling the Effects of Phospholipid Surfactants on Water and Nutrient Uptake

While the rhizosphere presents a different chemical, physical and biological environment to bulk soil, most experimental and modelling investigations of plant growth and productivity are based on bulk soil parameters. In this study, water and nutrient acquisition by wheat (Triticum aestivum L.) roots was investigated using rhizosphere- and root-system-scale modelling. The physical and chemical properties of rhizosphere soil could be influenced by phospholipid surfactants in the root mucilage. Two models were compared: a 2-dimensional (2D) Finite Element Method rhizosphere model, and a 3-dimensional (3D) root architecture model, ROOTMAP. ROOTMAP was parameterised to reproduce the results of the detailed 2D model, and was modified to include a rhizosphere soil volume. Lecithin (a phospholipid surfactant) could be exuded into the rhizosphere soil volume, decreasing soil water content and hydraulic conductivity at any given soil water potential, and decreasing phosphate adsorption to soil particles. The rhizosphere-scale modelling (5 × 5 mm² soil area, 10 mm root length, uptake over 12 h) predicted a reduction in water uptake (up to 16% at 30 kPa) and an increase in phosphate uptake (up to 4%) with lecithin exudation into the rhizosphere, but little effect on nitrate uptake, with only a small reduction in dry soil (1.6% at 200 kPa). The 3D root model reproduced the water (y = 1.013x, R² = 0.996), nitrate (y = 1x, R² = 1) and phosphate (y = 0.978x, R² = 0.998) uptake predictions of the rhizosphere model, providing confidence that a whole root system model could reproduce the dynamics simulated by a Finite Element Method rhizosphere model. The 3D root architecture model was then used to scale-up the rhizosphere dynamics, simulating the effect of lecithin exudation on water, nitrate and phosphate acquisition by a wheat root system, growing over 41 d. When applied to growing and responsive roots, lecithin exudation increased P acquisition by up to 13% in nutrient-rich, and 49% in relatively nutrient-poor soil. A comparison of wheat (Triticum aestivum L.) and lupin (Lupinus angustifolius L.) root architectures, suggested an interaction between the P acquisition benefit of rhizosphere lecithin and root architecture, with the more highly-branched wheat root structure acquiring relatively more P in the presence of lecithin than the sparsely-branched lupin root system.     

Microbial changes in clover rhizosphere after foliar and soil application of cobalt

Application of cobalt(II) nitrate to the leaves of red clover (Trifolium pratense L.) resulted in a pronounced increase of dry weight and the number of root nodules. Counts of bacteria in the rhizosphere, content of ammonia and production of carbon dioxide m rhizosphere soil were also higher, whereas the content of nitrates decreased Differences m the counts of bacteria, aotmomycetes, Azotobaoter, anaerobic bacteria and cellulose decomposing bacteria m the rhizosphere of control and treated plants were not directly related to the way of application of cobalt. GeneraPenicillium, Fusarium andTrichoderma predominated among fungi. The relative occurrence of pemcillia was higher after the application of cobalt, the incidence of fusaria was lower. The effects of foliar and soil application of cobalt on rhizosphere microflora were not identical.     

Effects of inorganic amendments (N,P and K) to soil on the rhizosphere microflora of antirrhinum plants infected withVerticillium dahliae Kleb

Summary A study of the inorganic amendments (N, P and K) to soil, and their effect on the rhizosphere microflora, as well as their relation to the control of wilt of antirrhinum plants caused byVerticillium dahliae Kleb. was done. Ammonium sulphate was the only chemical found to be significantly inhibitory toV. dahliae in vitro. Soil amendments (NPK) affected the rhizosphere microorganisms of the antirrhinum plants. Higher concentration of the chemicals were phytotoxic. It was further observed that ammonium sulphate, and the combined chemicals (NPK 25%) in soil delayed the senescence in healthy plants, suggests that chemical fertilisers affected the host plants directly. Addition of ammonium sulphate (0.25%), calcium nitrate (0.25%, 0.5%) combined NPK (0.25%) to soil caused considerable reduction in disease severity. It is assumed that this reduction may be caused by the (1) fungitoxic nature of the chemicali.e. ammonium sulphate, (2) antagonistic environment for the pathogen in the rhizosphere was boostedi.e. where calcium nitrate was added as soil amendments and (3) reduction in disease severity in soil-amended with combined NPK, may be due to the fact that antagonistic actinomycete population was boosted in the rhizosphere.     

Chemical Restraint of Exotic Animals in a Disease Regulatory Program

The African red tick (Rhipicephalus evertsi Neuman) is widely distributed in Africa but had never been identified in North America until September 1960 when it was found in a wild animal compound in Florida. The red tick is a vector of cattle fever (piroplasmosis) and several other exotic diseases including the highly fatal East Coast fever. The 130 acre compound contained more than 300 African and Asian animals, including giraffes, camels, zebras, elands, nilghais, blackbuck, aoudads, ostriches and Abyssinian asses. To determine the extent of the infestation, representative numbers of animals were immobilized with succinylcholine chloride for visual and manual examination. The grounds were treated with 2 lbs. of DDT per acre at three week intervals for six weeks and another group of animals were immobilized to determine the efficacy of the program. In all more than 50 wild animals were successfully immobilized with succinylcholine.     

复合菌剂调控连作当归根围土壤养分及对产量的影响

【背景】连作可引起微生物群落结构失调,导致土壤环境恶化、养分循环不畅、当归[Angelica sinensis (Oliv.) Diels]产量降低,通过现代微生物技术改良土壤、消减连作障碍势在必行。【目的】于大田条件下,研究施用复合菌剂对当归根围土壤酶活、速效养分及产量的影响,明确增产机制,改进增产措施。【方法】利用溶磷圈法检测不同菌株溶磷活性、乙炔还原法检测固氮活性、试剂盒法检测过氧化物酶和硝化能力;复合菌剂T1[荧光假单胞菌(Pseudomonas fluorescens)CBS5、产碱假单胞菌(Pseudomonas alcaligenes) CBS7、嗜冷假单胞菌(Pseudomonas extremaustralis)CBSB、生枝动胶菌(Zoogloea ramigera) CBS4]和T2 (荧光假单胞菌CBS5、产碱假单胞菌CBS7、嗜冷假单胞菌CBSB)及对照CK (无菌马铃薯葡萄糖肉汤培养基)分别处理连作当归,分光光度法测定根围土壤及根中养分循环、转化相关酶活,氮、磷、钾速效养分含量;常规方法测产量;统计软件进行相关数据方差分析和主成分分析。【结果】产碱假单胞菌C...     

Genetic Characterization of the Nitrate Reducing Community Based on <Emphasis Type="Italic">narG</Emphasis> Nucleotide Sequence Analysis

The ability of facultative anerobes to respire nitrate has been ascribed mainly to the activity of a membrane-bound nitrate reductase encoded by the narGHJI operon. Respiratory nitrate reduction is the first step of the denitrification pathway, which is considered as an important soil process since it contributes to the global cycling of nitrogen. In this study, we employed direct PCR, cloning, and sequencing of narG gene fragments to determine the diversity of nitrate-reducing bacteria occurring in soil and in the maize rhizosphere. Libraries containing 727 clones in total were screened by restriction fragment analysis. Phylogenetic analysis of 128 narG sequences separated the clone families into two main groups that represent the Gram-positive and Gram-negative nitrate-reducing bacteria. Novel narG lineages that branch distinctly from all currently known membrane bound nitrate-reductase encoding genes were detected within the Gram-negative branch. All together, our results revealed a more complex nitrate-reducing community than did previous culture-based studies. A significant and consistent shift in the relative abundance of the nitrate-reducing groups within this functional community was detected in the maize rhizosphere. Thus a substantially higher abundance of the dominant clone family and a lower diversity index were observed in the rhizosphere compared to the unplanted soil, suggesting that a bacterial group has been specifically selected within the nitrate-reducing community. Furthermore, restriction fragment length polymorphism analysis of cloned narG gene fragments proved to be a powerful tool in evaluating the structure and the diversity of the nitrate-reducing community and community shifts therein.     

海草根际微生物与海草植株的互作效应

【目的】本文以三亚湾泰来草根际沉积物为主要研究对象,研究室内培养条件下泰来草根际沉积物微生物对于高温处理和海草定殖的响应。【方法】通过对培养过程中水体物理化学参数(如pH、溶解氧、磷酸盐、硝酸盐、亚硝酸盐和铵盐)的监测以分析环境因子的变化;16S rRNA扩增子测序研究微生物群落结构的动态响应;通过荧光定量分析16SrRNA基因丰度变化。【结果】研究表明高温处理组在培养35 d后海水中磷酸盐、硝酸盐、亚硝酸盐和铵盐含量以及pH均要高于模拟原位环境的对照组,高温处理组根际沉积物微生物丰度在培养过程中呈现先上升后降低的趋势,同时,高温处理组根际微生物中初始阶段由厚壁菌门(32.4%)、变形菌门(22.92%)和梭杆菌门(27.21%)占据优势,培养一段时间后,厚壁菌门和梭杆菌门大幅度减少,逐渐被蓝细菌门和放线菌门所替代,最终由变形菌门(51.1%)占据主导地位,其中,属于硫还原细菌的脱硫杆菌科(Desulfobacteraceae)和硫氧化细菌的螺杆菌科(Helicobacteraceae)的细菌丰度不断提高。【结论】揭示了海草的定殖会提高高温处理后沉积物的多样性,并塑造和改善其根际沉积物微生物群落组成。     

3Hthymidine incorporation of rhizosphere bacteria influenced by plant N-status

The effect of plant-root N-status on bacterial growth in the rhizosphere was studied with 5-week-old wheat plants grown in soil with low N content obtained by mixing 9:1 gravel:sandy loam. As a consequence of N limitation, significant increase in³Hthymidine (Tdr) incorporation rate occured 3 days after addition of 30 mM ammonium compared to controls without ammonium. Plants were grown with split-roots to separate the effect of soil N from effect of plant root derived organic matter-N on bacterial activity. The increase in nitrate concentration from 10 mM to 30 mM at one part of the root system led to significant increased³HT dr incorporation in the rhizosphere at the other part of root system after 4 days showing that the composition of root exudates became more favourable for bacterial growth when plants were fertilized with the higher level of nitrate.     

Rhizosphere pH along different root zones of Douglas-fir (Pseudotsuga menziesii), as affected by source of nitrogen

Douglas-fir, grown on strongly acid soil (pH-H₂O 3.87), was fertilized with ammonium, nitrate or ammonium nitrate as N-source. Rhizosphere pH along the root axis was measured with microelectrodes. Pure ammonium supply resulted in acidification of the rhizosphere, almost along the entire root axis; only the extreme root tip was slightly alkaline compared with the bulk soil. With nitrate supply, the alkalization of the rhizosphere at the root tip was considerably stronger than with ammonium supply and the length of the alkalization zone greater, extending over the entire growth zone of the root. Acidification of the rhizosphere along the older parts of the root was less pronounced in the case of nitrate. It is concluded that nitrate nutrition enables the plant to protect its most essential root zone from the adverse effects of strong acidity by locally raising the rhizosphere pH.     

脲酶抑制剂/硝化抑制剂对植稻土壤中尿素N行为的影响

采用自制根盒试验,主要研究了脲酶抑制剂氢醌（HQ）,硝化抑制剂双氰胺（DCD）及二者组合对离水稻根际不同距离处NH4^--N和NO3^-N分布的影响,结果表明,DCD及其与HQ组合均能显著促进稻株地上部分生长,始终显著降低水稻根际与近根际土中NH4^ -N含量直至施肥后60d,施肥后20d时,DCD及其与HQ组合可使非根际土中NH4^ -N含量显著增加,随后,却出现相反现象,施肥后20d时,距根际不同距离的土壤中,配施DCD或DCD＋HQ处理均能显著降低NO3^-N含量,随后,近根际和非根际仍保持上述现象直至施肥后40d;同未施DCD处理相比,根际土壤却较早出现NO3^--N含量高峰,正好与水稻N营养需求时期相一致,因此,DCD及其与HQ组合可减少水稻根际环境下尿素N损失潜势,通过不种稻土壤和距根际3cm处的土壤中尿素无机氮形态分布的差异,充分显示了研究水稻根际土壤氮素转化及相关抑制剂对其影响时,以取离根际3cm外的土壤作为非根际明显优于不种稻土壤。