Mechanisms of fixation and release of ammonium in paddy soils after flooding III. Effect of the oxidation state of octahedral Fe on ammonium fixation

An experiment with two typical paddy soils from China and two clay minerals was conducted to study the effect of reduction of octahedral Fe^III on fixation of NH₄⁺ ions. Reduction of octahedral Fe^III was achieved by treating soils and clay minerals with dithionite‐citrate‐bicarbonate (DCB) followed by dialyzing the samples under oxygen free conditions. Reduction of Fe^III increased the negative charge of interlayers and resulted in a significantly higher ammonium fixation. Close positive correlations were found between the Fe²⁺ concentration or the ratio of Fe²⁺/Fe³⁺ and non‐exchangeable NH₄⁺‐N. Therefore, it is concluded that the reduction of octahedral Fe induced by flooding is one of the important prerequisites for the pronounced ammonium fixation in flooded soils. However, the relation between ΔFe²⁺ and Δfix‐N was not stoichiometric.     

Einfluß des Belastungsgrades unterschiedlicher Böden an ausgewählten Pestizid wirkenden Chlorkohlenwasserstoffen auf deren Aufnahme durch Möhren im Gefäßversuch

Influence of contamination of selected, pesticid effective hydrocarbons on their uptake by carrots in a pot experiment Exemplary soils from low up to higher grades of contamination with selected pesticid effective hydrocarbons (CHC) were used in a pot experiment on the uptake of these xenobiotica by carrot plants. Carrots are able to take up pesticid effective chlorinated hydrocarbons which was expected because of their oil cells and the lipophilic character of the examined substances. There is a correspondingly higher plant uptake from soils with a higher load of pollutants as from soils with a lower grade of contamination. Despite the high concentrations of beta- and alpha-HCH in the plants from the site Muldenaue (mg/kg dm] the total uptake per pot was relatively small (below 2 mg/pot). The transferfactors soil/plant show in all plant parts no enrichment of organochlorpesticides (foliage 0.021 < carrot body 0.156 < fine roots 0.975).     

Molecule cascades

Carbon monoxide molecules were arranged in atomically precise configurations, which we call "molecule cascades," where the motion of one molecule causes the subsequent motion of another, and so on in a cascade of motion similar to a row of toppling dominoes. Isotopically pure cascades were assembled on a copper (111) surface with a low-temperature scanning tunneling microscope. The hopping rate of carbon monoxide molecules in cascades was found to be independent of temperature below 6 kelvin and to exhibit a pronounced isotope effect, hallmarks of a quantum tunneling process. At higher temperatures, we observed a thermally activated hopping rate with an anomalously low Arrhenius prefactor that we interpret as tunneling from excited vibrational states. We present a cascade-based computation scheme that has all of the devices and interconnects required for the one-time computation of an arbitrary logic function. Logic gates and other devices were implemented by engineered arrangements of molecules at the intersections of cascades. We demonstrate a three-input sorter that uses several AND gates and OR gates, as well as the crossover and fan-out units needed to connect them.     

The force needed to move an atom on a surface

Manipulation of individual atoms and molecules by scanning probe microscopy offers the ability of controlled assembly at the single-atom scale. However, the driving forces behind atomic manipulation have not yet been measured. We used an atomic force microscope to measure the vertical and lateral forces exerted on individual adsorbed atoms or molecules by the probe tip. We found that the force that it takes to move an atom depends strongly on the adsorbate and the surface. Our results indicate that for moving metal atoms on metal surfaces, the lateral force component plays the dominant role. Furthermore, measuring spatial maps of the forces during manipulation yielded the full potential energy landscape of the tip-sample interaction.     

Phytochemical profile of main antioxidants in different fractions of purple and blue wheat, and black barley

Two pigmented wheat genotypes (blue and purple) and two black barley genotypes were fractionated in bran and flour fractions, examined, and compared for their free radical scavenging properties against 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt radical cation (Trolox equivalent antioxidant capacity, TEAC), ferric reducing antioxidant power (FRAP), total phenolic content (TPC), phenolic acid composition, carotenoid composition, and total anthocyanin content. The results showed that fractionation has a significant influence on the antioxidant properties, TPC, anthocyanin and carotenoid contents, and phenolic acid composition. Bran fractions had the greatest antioxidant activities (1.9-2.3 mmol TEAC/100 g) in all four grain genotypes and were 3-5-fold higher than the respective flour fractions (0.4-0.7 mmol TEAC/100 g). Ferulic acid was the predominant phenolic acid in wheat genotypes (bran fractions) while p-coumaric acid was the predominant phenolic acid in the bran fractions of barley genotypes. High-performance liquid chromatography analysis detected the presence of lutein and zeaxanthin in all fractions with different distribution patterns within the genotypes. The highest contents of anthocyanins were found in the middlings of black barley genotypes or in the shorts of blue and purple wheat. These data suggest the possibility to improve the antioxidant release from cereal-based food through selection of postharvest treatments.     

Feldmethode zur Bestimmung der substrat‐induzierten Bodenatmung

A field method for the measurement of substrate‐induced soil respiration A novel method for in situ measurements of microbial soil activity using the CO₂ efflux combined with kinetic analysis is proposed. The results are compared with two conventional, laboratory methods, (1) substrate‐induced respiration using a ’︁Sapromat’ and (2) dehydrogenase activity. Soil respiration was measured in situ after addition of aqueous solutions containing 0 to 6 g glucose kg^—1 soil. The respiration data were analysed using kinetic models to describe the nutritional status of the soil bacteria employing few representative parameters. The two‐phase soil respiration response gave best fit results with the Hanes' or non‐parametric kinetic model with Michaelis‐Menten constants (K_m) of 0.05—0.1 g glucose kg^—1 soil. The maximum respiration rates (V_max) were obtained above 1 g glucose. Substrate‐induced respiration rates of the novel in situ method were significantly correlated to results of the ’︁Sapromat’ measurements (r² = 0.81***). The in situ method combined with kinetic analysis was suitable for the characterisation of microbial activity in soil; it showed respiration rates lower by 59% than measured in the laboratory with disturbed samples.     

Differenzierte quantitative Erfassung der Nettoammonifikation durch Pilze und Bakterien in Böden unter verschiedenen Pflanzengesellschaften

Determination of ammonification rate by fungi and bacteria in soils with different plant societies. In soil samples of three sites in decidous forests with different plant-ecological and plant-sociological characteristics an attempt was made to determine the contributions of the saprophytic ammonifying fungi and bacteria by selective inhibition and by the use of a special incubation technique. The stimulation of the soil microflora was carried out by the addition of a universal-pepton as an easily degradable organic nitrogen. For the selective inhibition of fungi and bacteria the broad-spectrum antibiotics cycloheximide and streptomycinsulfate were used, which had been tested and found suitable by Anderson and Domsch (1973). The determinations of the produced fractions of inorganic nitrogen were conducted by the use of ion-specific eletrodes. During the short period of incubation lasting for a maximum of 8 hours, feasible for calculation, only the NH,-N-contents of the soil material increased while the contents of NO,-N and NO,-N did not change during this period. The average contributions of the ammonifying soil microflora was calculated as follows: site I 80 %by fungi/20 %by bacteria site II 80 % by fungi/20 % by bacteria site III 65 %by fungi/35 % by bacteria. A relationship between the contributions of ammonifying fungi and bacteria and ecological characteristics of the sites could not be found.