Effect of some biological factors on soil variability in the tropics

Summary Field observations were carried out on an Egbeda soil series in western Nigeria to study the degree of soil-nutrient variability within and between plots due to pre-clearing vegetation. The soil showed lower soil pH, organic C, exchangeable K and Ca contents following cassava grown by traditional methods than following secondary forest vegetation or thicket regrowth. Except for exchangeable K, the degree of variability of the above parameters was observed to be in the following order: secondary forest vegetation > thicket regrowth > cassava plots. The available P status was generally low and showed little relation to pre-clearing vegetation. The implications of soil variability due to pre-clearing vegetation on soil sampling and in field experimentation are discussed. re]19760204     

Effect of some abiotic factors on the biological activity of Gluconacetobacter diazotrophicus

AIMS: The effect of some abiotic factors, dryness, heat and salinity on the growth and biological activity of Gluconacetobacter diazotrophicus, and the influence of a salt stress on some enzymes involved in carbon metabolism of these bacteria is studied under laboratory conditions. METHODS AND RESULTS: Strain PAL-5 of G. diazotrophicus was incubated under different conditions of drying, heat and salinity. Cells showed tolerance to heat treatments and salt concentrations, and sensitivity to drying conditions. Higher NaCl dosage of 150 and 200 mmol l -1 limited its growth and drastically affected the nitrogenase activity and the enzymes glucose dehydrogenase, alcohol dehydrogenase, fumarase, isocitrate dehydrogenase and malate dehydrogenase. CONCLUSIONS: Gluconacetobacter diazotrophicus, despite its endophytic nature, tolerated heat treatments and salinity stress, but its nitrogenase activity and carbon metabolism enzymes were affected by high NaCl dosage. SIGNIFICANCE AND IMPACT OF THE STUDY: The investigation of the biological activity of G. diazotrophicus in response to different abiotic factors led to more knowledge of this endophyte and may help to clarify pathways involved in its transmission into the host plant.     

Temporal variability in the impact of river regulation on thermal regime and some biological implications

• 1 Ten years of hourly water temperature data for three river sites in south-west England were used to investigate the longer-term thermal effects of river regulation. The impact of reservoir impoundment on downstream invertebrate and trout development were simulated using daily mean temperature data in conjunction with published biological models.
• 2 The main effects of regulation on water temperature were to increase the mean value, eliminate freezing conditions, depress summer maxima, delay the annual cycle and reduce diel fluctuation. These impacts persisted over a distance of at least 5km below the dam but declined downstream, especially for seasonal and diurnal variations.
• 3 Simulations suggested that regulation is likely to have had a greater impact on the development of brown trout (Salmo trutta) than on the development of one Ephemeroptera and four Plecoptera species. Trout fry were predicted to emerge up to 57 days earlier, and to weigh up to 67% more by the end of the year following swim-up, in the regulated compared with the unregulated river.
• 4 Marked inter-annual contrasts in the physical and biological consequences of impoundment were evident, indicating that long-term studies are required to define properly the effects of river regulation.

     

Effect of dicumarol on the growth of some soil microorganisms.

The effect of dicumarol on growth of selected soil bacteria: Azotobacter chroococcum, Arthrobacter globiformis, A. citreus and Bacillus megaterium was studied. The following minimum concentrations were inhibitory in vitro: Arthrobacter citreus--20 mug/ml., Bacillus megaterium--40 mug/ml., Azotobacter chroococcum--40 mug/ml. Arthrobacter globiformis--70 mug/ml. Cells of all microorganisms studied grown in the presence of dicumarol developed aberrant morphological forms.     

Effect of non-ionic tensides on the growth of some soil bacteria

Summary The effect of some nonylphenyl-ethylene oxide polymers on the growth of Bacillus megaterium, B. cereus var. mycoides, B. polymyxa, B. subtilis, Pseudomonas fluorescence and Azotobacter chroococcum was investigated in the concentration range 20–800 ppm with the agar diffusion method. The zones of inhibition, restricted growth and eventual stimulation were determined with a Shimadzu C-930 dual wavelength TLC scanner. The data matrix was evaluated by principal component analysis. A. chroococcum was insensitive to each tenside at each concentration. The growth of the other microorganisms was inhibited by the tensides. With B. megaterium and B. cereus var. mycoides stimulation was also observed. The effect of the non-ionic tensides decreased with increasing length of the hydrophilic ethylene oxide chain. This phenomenon can be explained by the assumption that the activity of tensides depends on their membrane-damaging effect. The bulky nonylphenyl group inserts between the apolar fatty acid chains disorganizing the membrane structure. The longer hydrophilic ethylene oxide chain modifies the distribution of tenside between the apolar and polar regions of the membrane, preferring the aqueous phase. This results in the decrease or loss of biological activity.Offprint requests to: T. Cserháti     

Simple phosphate sorption index on some soils of the humid tropics

Summary Non linear relationships between c/x against c, and x against x/c at low equilibrium concentrations, were obtained for some Sierra Leone soils: where x = P sorbed, mg/ 100g; c = equilibrium P concentration, mol/liter. A single point index correlated well with isotherm slope; one of the uses to which this index can be put was illustrated.     

生物土壤结皮的分布影响因子及其监测

生物土壤结皮在荒漠化地区广泛分布。本文详细论述了生物土壤结皮的分布规律及其影响因素,如海拔高度、土壤、维管植物群落水分条件和干扰,以及生物土壤结皮在生态系统和景观变化监测和评价中的作用等。同时对中国西北地区生物土壤结皮的生态学研究和开发应用提供了研究的重点和方向。     

Effect of certain factors on the variability of strains of pertussis microbes

The population of degraded cells having stable changes in some phenotypical properties were isolated after subculturing some laboratory Bordetella pertussis strains in Bordet-Gengou culture medium and casein-charcoal agar with blood, treated with mitomycin C and allowed to proliferate in the spleen of mice injected intravenously with microbial suspensions. The characteristics indicative of cell degradation were the growth of large yellowish-white colonies appearing in 24 hours, the destruction of the agglutinogenic complex and toxic substances causing the atrophy of the spleen in mice, the increased capacity for active proliferation in the spleen. Electron-microscopic study revealed that the variants obtained by subculturing in culture media had the damaged membrane with the formation of cell-wall invaginations having rounded membrane-like formations on their surface, disappearing after treatment with mitomycin C; the treatment of the initial strains with mitomycin C resulted in cytoplasmic damage with the coagulation of the nucleoid.     

Spatial variability of soil fertility factors in the Xiangcheng tobacco planting region, China

It is essential to understand the spatial variability of soil properties in tobacco planting regions, so that the right decision can be made as to how many fertilizer rates are likely to be appropriated for the high-quality tobacco production. A total of 159 soil samples were taken from the surface soil (0-20cm) in the Xiangcheng tobacco planting fields, Henan Province, in April 2002 to examine the concentration of soil organic matter, pH, available N, available P, and available K. The spatial variability was evaluated using geostatistics and geographic information system (GIS) analyses. The results show that among those five soil fertility factors, the variation coefficient of soil pH was the smallest, while that of available P was the greatest, which resulted from different cultivation methods and uneven fertilization. Analysis of the isotropic variogram indicated that the soil pH, organic matter, and available P semivariogram were well described with spherical models, with the distance of spatial dependence being 21020, 19150, and 8460m, respectively, whereas the available N and available K semivariogram were well described with an exponential model, with the distance of spatial dependence being ranged from 7484 to 25320 m. Soil pH value was strongly spatially dependent with C0/sill being 0.1935, while the other four soil fertility factors were moderately spatially dependent with C0/sill ranging between 0.3528 to 0.5260. Through the Kriging analysis, the spatial distribution maps of soil properties were drawn using the arcview software. This study provides a scientific basis for field management, which targets soil quality improvement in the Xiangcheng tobacco planting region.     

Spatial variability of soil fertility factors in the Xiangcheng tobacco planting region, China

It is essential to understand the spatial variability of soil properties in tobacco planting regions, so that the right decision can be made as to how many fertilizer rates are likely to be appropriated for the highquality tobacco production. A total of 159 soil samples were taken from the surface soil (0-20 cm) in the Xiangcheng tobacco planting fields, Henan Province, in April 2002 to examine the concentration of soil organic matter, pH, available N, available P, and available K. The spatial variability was evaluated using geostatistics and geographic information system (GIS) analyses. The results show that among those five soil fertility factors, the variation coefficient of soil pH was the smallest, while that of available P was the greatest, which resulted from different cultivation methods and uneven fertilization. Analysis of the isotropic variogram indicated that the soil pH, organic matter, and available P semivariogram were well described with spherical models, with the distance of spatial dependence being 21020, 19150, and 8460 m, respectively, whereas the available N and available K semivariogram were well described with an exponential model, with the distance of spatial dependence being ranged from 7484 to 25320 m. Soil pH value was strongly spatially dependent with C0/sill being 0.1935, while the other four soil fertility factors were moderately spatially dependent with C0/sill ranging between 0.3528 to 0.5260. Through the Kriging analysis, the spatial distribution maps of soil properties were drawn using the arcview software. This study provides a scientific basis for field management, which targets soil quality improvement in the Xiangcheng tobacco planting region.     

Effect of some hygienic factors on family health

On the basis of longitudinal observations of a large group of town habitants the author determined some hygienic factors of direct as well as indirect influence on their health. The author elaborated a series of sanitary and hygienic recommendations believing that even in case of complete dispensarization of the population and assurance of suitable medical assistance, the physicians have all the same to take into consideration concentrate living conditions of each family.     

The solubility of manganese in some acid soils of the tropics

Summary Soil samples obtained from genetic horizons of two upland soils and an acid sulphate sub-soil of Sierra Leone West Africa, and crushed to pass a 2 mm sieve were equilibrated with 0.01M CaCl₂. Mn⁺² activity was estimated from measured total Mn, accounting where necessary for the MnSO₄⁰ complex specie.Mn⁺² activity was much lower than those predicted for equilibrium with a number of Mn minerals. It seems probable that known simple silicates, sulphates, phosphates, oxides and hydroxides of Mn are too soluble to persist in the fine earth fraction of these highly weathered soils of low pH. Observed Mn⁺² activity may be governed by exchangeable and/or other forms not evaluated here.