Use of microcalorimetry to study microbial activity during the transition from oxic to anoxic conditions

Microbial heat production is a nonspecific measure for microbial activity irrespective of O₂ availability in soils. In a series of long-term batch microcalorimeter experiments with closed ampoules, we examined the microbial activity in glucose-amended soil aggregates from different soil depths of a clay forest soil during the transition from aerobic to anaerobic conditions. Furthermore, the influence of the soil aggregate size on the long-term metabolic heat production was examined. Heat output curves showed a distinct pattern for soil samples from different soil depths and aggregate sizes and led to the following conclusions: 1. Microbial biomass and microbial activity strongly decreased with increasing soil depth as well as increasing soil aggregate size despite relatively constant organic C concentrations. 2. The transition from aerobic to anaerobic conditions led to a considerable drop in microbial activity. However, based on the energy balance, 10-26% of the heat production during the aerobic phase is attributable to anoxic or partly anoxic metabolism. 3. After O₂ exhaustion, a lag phase of low but constant heat output was observed, followed by a peak of anaerobic metabolic activity. Heat production during the lag phase was hypothesised to be an indicator for the biomass of facultatively anaerobic microorganisms in the soil.     

Ergebnisse von Simulationsrechnungen mit einem Bodenstickstoffmodell zur Düngung und zum Zwischenfruchtbau in Trinkwasserschutzgebieten

Results of computer simulations on fertilization and catch cropping problems in water protection areas by means of a soil nitrogen model A simple model of the nitrogen turnover in soil is presented. The model was validated by field experiment time series. The simulation results showed that dividing of the mineral nitrogen fertilization during spring for root crops or maize as well as shortening the first spring nitrogen fertilization for winter cereals diminished the leaching of nitrate only in extremely wet springs on sandy soils. The great importance of winter catch cropping in a cereal-root crop or a cereal-maize rotation on all soils and the necessity to avoid liquid manuring during late summer and early autumn, especially on sandy soils without catch cropping, are demonstrated. The results underline the predominant influence of the weather conditions on nitrate leaching.     

Über die Einwirkung heterotropher Mikroorganismen auf die Zersetzung silikatischer Minerale

The effect of heterotrophic microorganisms upon the degradation of silicate minerals The purpose of the present work was to study the weathering activity of yeasts and filamentous fungi on various silicate minerals. Culture experiments were carried out on samples of amphibolite, biotite, and orthoclase. Finely ground powder was incubated with pure cultures of 5 yeast strains and 11 filamentous fungi in a glucose-mineral salts-solution at room temperature over a period of 12 weeks. Changes in pH as well as in concentrations of K, Ca, Mg, Fe, Al, and Si in the culture solutions were determined at various intervals.-All fungal strains tested lowered the pH of the culture liquid with or without minerals added from 5.7 to values as low as 1.6. This acidification was brought about by the microbial production of organic acids, especially of gluconic acid. The lowest pH values were found in flasks containing biotite. Acidification in flasks with orthoclase was less pronounced. The pH values found in flasks containing amphibolite were similar to those produced in cultures without mineral powder. From biotite, up to 62% K, 33% Mg, 29% Fe, 59% Al, and 6% Si were released. The solubilizing activity on orthoclase was less effective, and least that on amphibolite.-The importance of acidity and the chelating capacity of the microbially produced organic acids as well as the chemical and structural properties of the mineral with respect to weathering are discussed. The results show that heterotrophic microorganisms like yeasts and filamentous fungi may effectively attack silicate minerals and rocks.     

Role of aggregate surface and core fraction in the sequestration of carbon from dung in a temperate grassland soil

The sequestration of dung carbon in soil depends on the location and rate at which it is immobilized in soil aggregates. Here C₄ dung (δ¹³C = ?16.1‰) or C₃ dung (δ¹³C = ?26.8‰) were applied to a temperate permanent pasture C₃ soil (δ¹³C = ?27.9‰). Triplicate samples were taken from C₃ and C₄ dung remaining at the surface, and in the 0–1 and 1–5 cm soil layers in the unamended control and under the C₃ and C₄ dung patches after 7, 14, 29, 42 and 70 days after the application of the dung. Macroaggregates (≥ 4 mm) at the lower depth (1–5 cm) were mechanically fractionated into surface and core fractions by a combination of shock freezing followed by wet sieving. Neither overall nor differential carbon isotope fractionation occurred in the dung remaining at the surface. The incorporation of C₄ dung significantly increased the δ¹³C content of the 0–1 cm layer of the C₃ soil. Dung C sequestration did not exceed 10% for the 0–1 cm layer and was only 20% for the whole soil (0–30 cm) during the 7‐day experiment. Only 32–66% of the C from dung in the 1–5 cm layer was sequestered in the aggregates; the major proportion was initially preferentially attached to their surfaces, but incorporated into aggregates within the following 14 days. The majority of dung, however, soon resided between the aggregates, pointing to the important role of the inter‐aggregate fraction in short‐term C dynamics of dung in this pasture soil.     

Fiber-optical analog of the event horizon

The physics at the event horizon resembles the behavior of waves in moving media. Horizons are formed where the local speed of the medium exceeds the wave velocity. We used ultrashort pulses in microstructured optical fibers to demonstrate the formation of an artificial event horizon in optics. We observed a classical optical effect: the blue-shifting of light at a white-hole horizon. We also showed by theoretical calculations that such a system is capable of probing the quantum effects of horizons, in particular Hawking radiation.     

Surface of young Jupiter family comet 81P/Wild 2: view from the Stardust Spacecraft

Images taken by the Stardust mission during its flyby of 81P/Wild 2 show the comet to be a 5-kilometer oblate body covered with remarkable topographic features, including unusual circular features that appear to be impact craters. The presence of high-angle slopes shows that the surface is cohesive and self-supporting. The comet does not appear to be a rubble pile, and its rounded shape is not directly consistent with the comet being a fragment of a larger body. The surface is active and yet it retains ancient terrain. Wild 2 appears to be in the early stages of its degradation phase as a small volatile-rich body in the inner solar system.     

A central role of salicylic Acid in plant disease resistance

Transgenic tobacco and Arabidopsis thaliana expressing the bacterial enzyme salicylate hydroxylase cannot accumulate salicylic acid (SA). This defect not only makes the plants unable to induce systemic acquired resistance, but also leads to increased susceptibility to viral, fungal, and bacterial pathogens. The enhanced susceptibility extends even to host-pathogen combinations that would normally result in genetic resistance. Therefore, SA accumulation is essential for expression of multiple modes of plant disease resistance.     

Isotopic evidence for glaciation during the Cretaceous supergreenhouse

The Turonian (93.5 to 89.3 million years ago) was one of the warmest periods of the Phanerozoic eon, with tropical sea surface temperatures over 35 degrees C. High-amplitude sea-level changes and positive delta18O excursions in marine limestones suggest that glaciation events may have punctuated this episode of extreme warmth. New delta18O data from the tropical Atlantic show synchronous shifts approximately 91.2 million years ago for both the surface and deep ocean that are consistent with an approximately 200,000-year period of glaciation, with ice sheets of about half the size of the modern Antarctic ice cap. Even the prevailing supergreenhouse climate was not a barrier to the formation of large ice sheets, calling into question the common assumption that the poles were always ice-free during past periods of intense global warming.     

Chromosomal location of powdery mildew resistance genes in common wheat (Triticum aestivum L. em. Thell.) 3. Gene Pm22 in cultivar Virest

Summary Common wheat cultivar Virest possesses mildew resistance which is different from resistances expressed by currently documented mildew resistance genes, detected by response to eleven differential wheat powdery mildew isolates. F₂ populations from hybrids of the 21 Chinese Spring monosomic lines with Virest revealed one major dominant gene, located on wheat chromosome 1D. The new gene is designated Pm22. Italian cultivars Elia, Est Mottin, Ovest and Tudest also showed the disease response pattern corresponding to Virest.