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.

---

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 composted textile sludge on growth, nodulation and nitrogen fixation of soybean and cowpea

The effect of composted textile sludge on growth, nodulation and nitrogen fixation of soybean and cowpea was evaluated in a greenhouse experiment. The compost was incorporated into soil at 0, 9.5, 19 and 38 t ha(-1) (bases upon the N requirement of the crops, i.e., 0, 50, 100 and 200 kg available N ha(-1)). Growth, nodulation and shoot accumulation of nitrogen were evaluated 36 and 63 days after plant emergence. Nodule glutamine synthetase (GS) activity and leghemoglobin content were evaluated 63 days after emergence. Composted textile sludge did not show negative effects on nodule number and weight, nodule GS activity and leghemoglobin content. Nitrogen accumulation in shoot dry matter in soybean and cowpea was higher than other treatments with application of 19 t ha(-1) of compost. Composting can be an alternate technology for the management of solid textile mill sludge. This study verifies that the composted textile sludge was not harmful to growth, nodulation and nitrogen fixation of soybean and cowpea.     

Effect of high soil temperatures on nodulation of cowpea, Vigna unguiculata

Cowpeas, inoculated with one of five effective strains of Rhizobium isolated from African soils, were grown at root temperatures of 30 ^oC continuously or at 36, 38, 40, 42 and 44 ^oC for 5 h/day and returned to glasshouse ambient for the intermediate period. Growth was best at 30 and 36 ^oC; above 40 ^oC growth was poor and no nodules formed. At 40 ^oC two strains failed to nodulate. Symbiotic performance was not dependent only on nodule production as nodule efficiency varied inversely with temperature. The number of nodules formed by strain R5000 after exposure of inoculated seed or seedlings to 40,42 or 44 ^oC for 5 h/day on each of 3 or 6 days depended on the age of plant and the duration of exposure to stress. When exposed to 42 or 44 ^oC during the first 3 days after sowing nodulation was reduced from 18 to 1–3 nodules/plant even after a further 40 days growth at ambient (30 day, 20 ^oC night). Nodulation was unaffected when 10–15-day-old seedlings were exposed to the same conditions. Numbers of strain R5000 on seed declined rapidly following three daily exposures of 5 h at 39 and 42 ^oC; at 45 ^oC less than three bacteria survived on each seed. Other rhizobia of the cowpea group varied greatly in their toleration of high temperatures, some survived well at 45 ^oC whereas others behaved like R5000.     

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.     

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.     

Effect of soil solarization on nodulation,infection by mycorrhizal fungi and yield of cowpea

Solarization of soil was found beneficial for plant growth in cowpea under field conditions. Root nodulation, infection by mycorrhizal fungi and yield were higher in plants grown in solarized soil. These increases were to the extent of 104.7, 20.0 and 23.7 per cent respectively when compared to control treatment without solarization.     

Effect of continuous application of manures and fertilizers on rhizosphere microflora in arecanut palm

Summary The rhizosphere microflora of arecanut palm under continuous application of organic manures and inorganic fertilizers was studied. The nutrients applied are 100 g N, 40 g P₂O₅ and 140 g K₂O/palm/year in the form of organics and inorganics. The application of organic manure increased the microbial population. The increase in microbial population was observed between the rhizosphere samples collected at 0–30cm and 30–60 cm depths. The surface cultivation of soil increased the microbial population.Trichoderma sp. andAspergillus sp. dominated in therhizosphere of arecanut palm. Contribution No. 208. Central Plantation Crops Research Institute, Vittal-574243, Karnataka, India.     

Effect of phosphorus on the colonization of barley rhizosphere by microorganisms

The mineral phosphorus supply produced two outbreaks in the bacterial population of the barley rhizosphere and rhizoplane but inhibited the growth of fungal mycelium. The inhibition of mycelial growth might be due to the exudation of specific inhibitors by barley roots, since the most pronounced inhibition was observed at high doses of supplementary phosphorus.     

Effect of carbofuran on the growth and nodulation ofVigna radiata

Effect of carbofuran on the growth, nodulation, phytomass, chlorophyll and carotene ofVigna radiata Roxb., was studied. Out of different concentrations of carbofuranviz., 0, 5, 10, 25, 50 and 100 ppm, the concentration of 5 ppm carbofuran revealed no toxic effect, instead the growth, number of nodules, phytomass and chlorophyll were increased in comparison to control. However, 10, 25 and 50 ppm carbofuran proved to be toxic. The plants showed inhibition of growth. While 100 ppm of carbofuran was found to be fatal for the growth of plants.     

Seven in absentia proteins affect plant growth and nodulation in Medicago truncatula

Protein ubiquitination is a posttranslational regulatory process essential for plant growth and interaction with the environment. E3 ligases, to which the seven in absentia (SINA) proteins belong, determine the specificity by selecting the target proteins for ubiquitination. SINA proteins are found in animals as well as in plants, and a small gene family with highly related members has been identified in the genome of rice (Oryza sativa), Arabidopsis (Arabidopsis thaliana), Medicago truncatula, and poplar (Populus trichocarpa). To acquire insight into the function of SINA proteins in nodulation, a dominant negative form of the Arabidopsis SINAT5 was ectopically expressed in the model legume M. truncatula. After rhizobial inoculation of the 35S:SINAT5DN transgenic plants, fewer nodules were formed than in control plants, and most nodules remained small and white, a sign of impaired symbiosis. Defects in rhizobial infection and symbiosome formation were observed by extensive microscopic analysis. Besides the nodulation phenotype, transgenic plants were affected in shoot growth, leaf size, and lateral root number. This work illustrates a function for SINA E3 ligases in a broad spectrum of plant developmental processes, including nodulation.     

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.     

Effect of seed size and plant growth on nodulation and nodule development in lima bean (Phaseolus lunatus L.)

Lima bean (Phaseolus lunatus L.) cultivars vary widely in their growth habit and seed size. Preliminary experiments indicated that a large-seeded pole cultivar (King of the Garden) formed many more nodules than a small-seeded bush cultivar (Henderson). The relative importance of seed size and shoot mass in determining nodule number and mass was assessed in five lima bean cultivars differing in seed size and growth habit. Between cultivars, significant positive correlations between initial seed mass, plant weight and nodule number and mass were observed during the first four weeks after planting. Comparisons within cultivars indicated a strong correlation between nodule mass and shoot dry weight. The influence of plant morphology on nodule formation and mass was secondary to the effects of seed and shoot mass. As plants matured, the increase in nodule mass paralleled the increase in plant mass, while nodule number was relatively stable after day 18. These results suggest that the highly regulated process of nodule formation was under the influence of seed derived factors, while the continued accumulation of nodule tissue was related to shoot growth.     

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     

Effect of plant growth hormones and polyamines on ornithine decarboxylase activity during the germination of barley seeds

Gibberellic acid (GA₃) and β-indolylacetic acid (IAA), two of the well known growth hormones, induce four fold the activity of ornithine decarboxylase (ODC) during the germination of barley seeds ( Hordeum vulgare L. var. Beca). The optimal concentration for induction of ODC was 10^–5 M for GA₃ and 10^–3 M for IAA. When 10^–3 M of a polyamine, putrescine or spermidine, is added to the growth medium, ODC activity is significantly inhibited. This inhibition is due to the induction of a protein inhibitor of ODC (antizyme), whose apparent molecular weight is 16 000 ± 2 000 daltons. Addition of GA₃ to cultures which have been grown for 50 or 98 h in the presence of polyamines, abolishes the observed inhibition of ODC activity, while in the reverse experiment, addition of polyamines at 50 or 98 h does not affect the ODC activity induced by GA₃. Cadaverine, a physiological plant diamine, enhances ODC activity; whereas 1,8-diaminooctane (the alkyl analogue of spermidine) does not have any effect.     

Effect of dieldrin and lindane on the growth and nodulation ofVicia faba

The chlorinated hydrocarbon insecticides, dieldrin and lindane, were used at the normal and 20-fold rate. The plants were grown in pots containing clay soil. The results showed that whereas low and high concentrations of dieldrin as well as low concentration of lindane had no effect on the morphological characters of the shoot and root systems, high concentration of lindane had a harmful effect. Nodulation was slightly affected by low and high concentrations of dieldrin as well as low concentration of lindane. High concentration of lindane had a deleterious effect on nodulation.     

Effect of growth irradiance on plastocyanin levels in barley

Plastocyanin levels in barley (Hordeum vulgare cv Boone) were found to be dependent on growth irradiance. An immunochemical assay was developed and used to measure the plastocyanin content of isolated thylakoid membranes. Barley grown under 600 mole photons m^–2s^–1 contained two- to four-fold greater quantities of plastocyanin per unit chlorophyll compared with plants grown under 60 mole photons m^–2s^–1. The plastocyanin/Photosystem I ratio was found to be 2 to 3 under high irradiance compared with 0.5 to 1.5 under low irradiance. The reduced plastocyanin pool size in low light plants contributed to a two-fold reduction in photosynthetic electron transport activity. Plastocyanin levels increased upon transfer of low light plants to high irradiance conditions. In contrast, plastocyanin levels were not affected in plants transferred from high to low irradiance, suggesting that plastocyanin is not involved in the acclimation of photosynthesis to shade.Abbreviations: BSA bovine serum albumin - chl chlorophyll - cyt cytochrome - DCIP 2,6-dichlorophenolindophenol - PS I Photosystem I - PS II Photosystem II - P700 reaction center of Photosystem I - TBS 20 mM Tris-HCl pH 7.5, 500 mM NaCl - TTBS 20 mM Tris-HCl pH 7.5, 500 mM NaCl, 0.5% (w/v) polyoxyethylenesorbitan monolaurate (Tween-20)     

Aphid effects on rhizosphere microorganisms and microfauna depend more on barley growth phase than on soil fertilization

This paper gives the first reports on aphid effects on rhizosphere organisms as influenced by soil nutrient status and plant development. Barley plants grown in pots fertilized with N but without P (N), with N and P (NP), or not fertilized (0) were sampled in the early growth phase (day 25), 1 week before and 1 week after spike emergence. Aphids were added 16 days before sampling was carried out. In a separate experiment belowground respiration was measured on N and NP fertilized plant–soil systems with aphid treatments comparable to the first experiment. Aphids reduced numbers of rhizosphere bacteria and fungal feeding nematodes 1 week before spike emergence. Before spike emergence, aphids reduced belowground respiration in NP treatments. These findings strongly indicate that aphids reduced allocation of photoassimilates to roots and deposition of root exudates in the growth phase of the plant. Contrary to this, 1 week after spike emergence numbers of bacteria, fungal feeding nematodes and Protozoa were higher in rhizospheres of plants subjected to aphids probably because aphids enhanced root mortality and root decomposition. Protozoa and bacterial feeding nematodes were stimulated at different experimental conditions with nematodes being the dominant bacterial grazers at N fertilization and Protozoa in the NP treatment before spike emergence.