Einfluß von Wassergehalt und Salzen auf die Nitrifikation in Proben einer podsoligen Braunerde

Influence of watercontent and salts on the nitrification in samples of a Dystric Cambisol Samples of a Dystric Cambisol from a beech site produced nitrate but autotrophic nitrifying microorganisms could not be detected. Net nitrification of the humic layer and the upper 5 cm of the mineral soil during incubation at 22°C was investigated. Nitrification rate increased with increasing water content of the soil. Additions of ammonium or peptone did not increase the nitrification in the humic layer. Supply of (ammonium-)sulphates and chlorides with concentrations higher than 2 mMol per kg soil inhibited nitrification totally. This could not be ascribed to pH-changes. Additions of phosphates, lime or alkali to the soil samples increased nitrification.     

The variability of the apparent diffusion coefficient in undisturbed soil columns

In column studies in the laboratory the apparent diffusion coefficients(D)of chloride and TOH for undisturbed and unsaturated soils were determined as a function of the pore water velocity. Parallel the effective diffusion coefficients (D⁺) of Cl^? were measured as a function of water content. It was found that the values of D varied significantly between soil layers and soil types. This findings also held for the low flow velocities studied (0.3 and 1.0 cm/d). The impedance factors to calculate the effective diffusion coefficients (D⁺) from D values in the bulk water, decreased with decreasing bulk densities. In model calculations it was demonstrated that in spite of the differences of D values measured, for many purposes in the field good estimates of the solute distribution in the soils can be obtained by using simple relations between D and v_o.     

The water balance of a sugar beet crop: A model and some experimental evidence

For a loes soil with sugar beets (Beta vulgaris L.) a model was developed with which the difficult-to-measure components of the water balance equation can be determined. Basic component of the model is the unsaturated soil moisture flow equation. This equation is solved numerically by a finite difference method. As boundary condition at the soil surface, expressions for the potential and the actual transpiration and for the potential and the actual evaporation are used. Besides the hydraulic functions of the soil, standard meteorological measurements, together with leaf area index and root distribution data of the crop, enter the model. For a period of 316 days, calculated and measured soil suction values in 10 different soil depths, are compared as well as transpiration and seepage vaules. The comparison shows that the model provides acceptable results. The model calculations indicate that of the 519 mm of precipitation received during the 316-day period, 503 mm were used for evapotranspiration and 119 mm left the soil profile as internal seepage.     

Transformation of simulated wet sulfate deposition in forest soils assessed by a core experiment using stable sulfur isotopes

The effects of elevated atmospheric SO ₄ ^2? deposition on S cycling in forest soils were assessed in an irrigation experiment using stable S isotopes. Over a period of 20 months, core lysimeters of five acidic forest soils from Southern Germany with different parent material and pedogenesis were irrigated with solutions chemically similar to canopy throughfall. Sulfate deposition in three experimental variants corresponded to 23, 42 and 87 kg S ha^?1 yr^?1. The SO ₄ ^2? used for irrigation had aδ ³⁴S ratio of +28.0‰ CDT (Canon Diablo Troilite standard), differing by more than +25‰ from natural and anthropogenic S in Southern Germany. A combination of chemical and isotopic analyses of soil and seepage water samples was used to elucidate the fluxes and transformations of simulated wet SO ₄ ^2? deposition in each soil core. Retention of experimentally deposited S ranged from 57±5% in coarse-grained soils low in sesquioxides and clay, to 80±8% in loamy soils with high sesquioxide content. The sesquioxide content proved to be the major factor governing S retention. The ratio of S retained as inorganic SO ₄ ^2? (mainly by adsorption) to that incorporated into organic compounds (presumably by microbial synthesis) ranged from 2 to 4. For the organic S pool, the amount of S retained as C-bonded S exceeded by far that immobilized as ester sulfate in four of the five soils. Application of³⁴S-enriched SO ₄ ^2? appears to be a suitable experimental tool to assess fluxes and transformations of deposited S in forest soils, if aerobic conditions are maintained. In contrast to radioactive S tracers, the concept should be applicable not only in laboratory and lysimeter experiments, but also in long term studies of whole forest ecosystems (e.g., experimental watersheds).     

Glycosylated compounds from okra inhibit adhesion of Helicobacter pylori to human gastric mucosa

In Asian medicine the fruit of the okra plant, Abelmoschus esculentus (L.) Moench., is used as a mucilaginous food additive against gastric irritative and inflammative diseases. To find a rational basis for its use against these diseases, several crude and purified carbohydrate-containing fractions from immature okra fruits were isolated and analyzed, and their effects against Helicobacter pylori in an in situ adhesion model on sections of human gastric mucosa were determined. Pretreatment of the bacteria with a fresh juice preparation inhibited the bacterial adhesion almost completely. Lyophilization and reconstitution of an extract solution led to a reduction of this effect. A crude polysaccharide (RPS) isolated from the fresh juice by ethanolic precipitation showed strong inhibitory effects. Further fractionation of RPS revealed a purified, highly acidic subfraction (AF III) with high antiadhesive qualities. Carbohydrate analysis revealed the presence of rhamnogalacturonans with a considerable amount of glucuronic acid, whereas other inactive subfractions contained little glucuronic acid or were glucuronic acid-free. After heat denaturation of the fresh juice or protein precipitation with 5% TCA the antiadhesive activity of the fresh extract was reduced, indicating that besides polysaccharides, protein fractions also exhibited antiadhesive properties. SDS-PAGE analysis of the precipitate revealed several bands of glycosylated proteins between 25 and 37 kDa that were almost diminished in the nonactive supernatant. Preincubations of gastric tissue with any of the active fractions did not lead to reduced bacterial binding. The antiadhesive activity is therefore due to the blocking capacity of specific Helicobacter surface receptors that coordinate the interaction between host and bacterium. Neither of the active fractions showed inhibitory effects on bacterial growth in vitro. The antiadhesive qualities of okra were assumed to be due to a combination of glycoproteins and highly acidic sugar compounds making up a complex three-dimensional structure that is fully developed only in the fresh juice of the fruit.     

Der jetzige Stand der Maiszünsler-Frage in Deutschland

Ohne Zusammenfassung Mit 1 Abbildung.