Efficiency of acetylene reduction (nitrogen fixation) in soil: Effect of type and concentration of available carbohydrate

Sandy loam field soil and Acer saccharum (maple) forest soil were amended with different concentrations of glucose and mannitol and incubated at different pO₂ levels. Nitrogenase activity was determined by repeated 1-h C₂H₂ reduction assays performed at the ambient pO₂ of incubation. Calculated efficiencies of N₂ fixation increased with increasing anaerobiosis and with decreasing added carbohydrate concentration. Efficiencies up to 30 mg N₂ fixed per gram of glucose consumed were obtained under anaerobic conditions in the presence of 0.25% (w/w) glucose. Evidence suggested that low aerobic efficiencies were caused by intense competition for carbohydrate and by lower pH values attained. High concentrations (up to 3.0% w/w) of glucose under aerobic conditions suppressed the development of N₂ase activity. Mannitol supported N₂ase activity the development of which was very much delayed under aerobic conditions but little delayed under anaerobic conditions.     

Variability in sesquiterpene lactones from the leaves of yacon (Smallanthus sonchifolius) accessions of different geographic origin

The sesquiterpene lactones (STLs) content of glandular trichomes from the leaves of twenty-five yacon (Smallanthus sonchifolius, Asteraceae) accessions, obtained along a latitudinal gradient from Ecuador to northwest Argentina, was characterized by gas chromatography/mass spectroscopy (GC/MS). While accessions from Ecuador, Bolivia and Argentina proved to be very chemoconsistent, significant variation was found in quantitative composition of STLs from accessions in central Peru, the probable region of origin for the species.     

Differences in the fragrances of pollen,leaves, and floral parts of garland (Chrysanthemum coronarium) and composition of the essential oils from flowerheads and leaves

Headspace analyses of pollen, whole flowerheads, ligulate and tubular florets, flower buds, involucral bracts, and leaves have been performed on the food plant Chrysanthemum coronarium L. (Asteraceae). The analyses permitted differences in the pattern of volatiles emitted by the different floral parts to be observed and the site and phenological stage of emission of these chemicals to be verified. Camphor and cis-chrysanthenyl acetate were emitted mainly by ligulate and tubular florets; the production of myrcene and (Z)-ocimene was higher in the flower buds, whereas beta-caryophyllene, (E,E)-alpha-farnesene, and (E)-beta-farnesene seemed attributable mainly to the involucral bracts. The leaves showed a quite different volatile profile, with (Z)-ocimene as the main constituent. Pollen showed a completely different composition of its volatiles, with perilla aldehyde, cis-chrysanthenyl acetate, and camphor among the principal compounds; many carbonylic compounds and linear hydrocarbons have been detected exclusively in pollen. Furthermore, the essential oils obtained from flowerheads and leaves have been studied. These samples showed mainly quantitative differences. Camphor (22.1%) and cis-chrysanthenyl acetate (19.9%) were the main constituents of the oil from flowers, whereas the oil from the leaves contained mainly (Z)-ocimene (45.4%) and myrcene (28.2%).     

The role of alkaloids in the feeding behaviour of slugs (Gastropoda: Stylommatophora) as pests of narrow-leafed lupin plants

The degree of damage done to lupin plants by slugs is highly dependent on the species and the cultivar of plant. A study was carried out, in laboratory conditions and on small plots, to investigate the extent of damage done to plants of eight cultivars of narrow-leafed lupin when exposed to grazing by Arion vulgaris, Arion rufus and Deroceras reticulatum. Five sweet and three bitter cultivars of lupin were selected, respectively, having low- and high-alkaloid content. The contents of the dominant lupine alkaloids in these plants were determined. It was found that the susceptibility of the plants to slug damage is dependent on their content of alkaloids. The plants of high-alkaloid cultivars (Karo, Mirela and Oskar) were less heavily damaged by the studied species of slugs. The greatest differences were recorded for A. vulgaris and D. reticulatum, while the differences for A. rufus were smaller. For all studied slug species, the differences were statistically significant. The results of carried out experiments may potentially be of use in the selection of cultivars of Lupinus angustifolius to be grown in areas inhabited by these slug species.     

Activities and results of the terrestrial effects program: Acid precipitation in ontario study (APIOS)

Studies on the terrestrial effects of acidic precipitation in Ontario involve determining the effects on .soils, crops, forests, lichens, mosses and biogeochemical systems. In the soils program, a baseline study was started in 1980 to establish a reliable and uniform data base for soils across the province, in order to identify future trends. Soil sensitivity criteria are being derived for mapping purposes. Starting in 1982, a complex, sophisticated mobile rain exclusion canopy system was constructed outdoors for controlled acid rain studies to determine the dose-response relationships of field crops. In response to numerous complaints a program was designed to determine the role that acidic precipitation is playing in the decline of sugar maple trees in Ontario. At 8 sites, tree conditions were noted, samples of foliage, bark, roots and soil were collected for chemical analysis, and increment cores and discs (from felled trees) were taken for radial growth patterns. Results from this study indicated that acidic precipitation was an additional stress to insect outbreaks and spring droughts. Intensive surveys have been conducted in selected areas in Ontario to identify the current viability and distribution of common denominator lichens and mosses. Biogeochemical studies are being conducted at four watersheds in Ontario. The different watersheds are located in progessively decreasing atmospheric deposition loadings from east to west across the province. The studies are attempting to document the role of contrasting terrestrial ecosystems in the process of lake acidification by atmospheric deposition.     

Transformations and neoformations of clay in the cryogenic environment: examples from Transbaikalia (Siberia) and Patagonia (Argentina)

Permafrost desiccates and indurates soil horizons. During summer, the perennially frozen ground under the active thawed layer creates confined conditions, Whereas in winter the closed system between the permafrost and the freezing front migrating downwards leads to irreversible changes in the soil structure and to transformation and neoformation of minerals. Two examples were studied by field observation and laboratory analyses (optical microscopy, scanning electron microscopy, X-ray diffractometry, transmission electron microscopy and analytical electron microscopy). In Transbaikalia (southeastern Siberia) a Pleistocene cryogenic slope deposit on syenite contains detrital clays (chlorite, illite), but neoformed ferroan smectites dominate. In Patagonia, centimetre-sized silica concretions containing spongy and spheroidal opal occur in alluvium ascribed to cold Pleistocene periods. They seem to have formed from primary detrital smectite that was transformed to fibrous clay (sepiolite) then to acicular opal, and eventually to spheroidal opal. The neoformed opal contains 27% magnesium. These features occur systematically within fossil cryoturbations not related to present conditions. It appears that clay transformation and neoformation can happen at temperatures far lower than 0°C.     

Iron and sulfate reduction in the sediments of acidic mine lake 116 (Brandenburg,Germany): Rates and geochemical evaluation

A combination of rate measurements of iron(III)oxide and sulfate reduction, thermodynamic data, and pore-water and solid phase analyses was used to evaluate the relative significance of iron and sulfate reduction in the sediments of an acidic strip mining lake (Lake 116, Brandenburg, Germany). The rate of sulfate reduction was determined using a 35S-radiotracer method. Rates of iron turnover were quantified by mass balances based on pore-water concentration profiles. The differences in Gibbs free energy yield from reduction of iron and sulfate and from methanogenesis were calculated from individual redox couples and concentrations of reactants to account for the influence of high Fe2+ concentrations and differing mineral phases. Integrated (O-20 cm) mean rates of sulfate reduction were 1.2 (pelagial), respectively 5.2 (littoral) mmol (m2d)-1. Based on electron equivalents, the estimated iron reduction rates reached between about 50 % (pelagial) and 75 % (littoral) of the sulfate reduction rates. Compared to conditions usually assumed in the literature, in the sediments Gibbs free energy advantage of iron reduction over sulfate reduction was reduced frmm +11 KJeq-1 to a range of about +7 KJeq-1 (ferrihydrite, "reactive iron") to -6 KJeq-1 (goethite). This indicates that iron reduction was thermodynamically favored to sulfate reduction only if amorphous iron(III)oxides were available and is in accordance to the high competitiveness of sulfate reducers in the sediment. While total iron concentration in the sediments was high (up to 80% of the dryweight), reactive iron only accounted for 11-38% and was absolutely and relatively diminished in the zone of iron reduction. Pore-water concentration gradients and 137CS profiles indicated that little or no bioturbation occurred in the sediments, probably inhibiting the renewal of reactive iron. We further hypothesize that the reactivity of the iron oxide surfaces was reduced due to adsorption of DOM, suggested by IR spectra of the DOM and by a surface coverage estimate using literature data. Pelagial and littoral sediments displayed different dynamics. At the littoral relative iron reduction rate estimates were higher, iron sulfides were not accumulated and residence times of iron oxides were short compared to the pelagial. At the littoral site reoxidation of iron sulfides probably resulted in the renewal of reactive iron(III)oxides, possibly allowing for higher relative rates of iron reduction.     

Check dams and sediment control: final results of a case study in the upper Corneja River (Central Spain)

Journal of Soils and Sediments - The sediment yield and erosion rate in an area can be estimated by calculating the volume of sediment retained by check dams. However, results can show unrealistic...     

传染性支气管炎病毒青岛腺胃分离株（SD／97／02）核衣壳蛋白基因的序列测定和分析

传染性支气管炎病毒(IBV)为冠状病毒科,冠状病毒属套式病毒目(Nidovirilaes).此病毒可引起鸡急性、高度接触性传染病.IBV的基因组具有先导--引物转录机制,使病毒具有很高的变异率.现已有呼吸型、肾型、肠型和减蛋型.1995年,中国出现一种以腺胃病变为主要特征的鸡传染病,初步鉴定为IBV的又一变异株.IBV的结构蛋白包括纤突蛋白(s1)、基质蛋白(M)和核衣壳蛋白(N).现在大多数研究的重点集中在使机体诱导特异性的中和抗体.纤突蛋白基因s1亚单位上,S1基因的5′末端的高变区(highvariationregion,HVR)的微小变异即可导致毒株之间不能互相保护甚至产生新的组织嗜型.     

Reactivation of old landslides: lessons learned from a case-study in the Flemish Ardennes (Belgium)

The number of human‐induced landslides is increasing worldwide, but information on the impact of human intervention on slope stability is often lacking. Therefore, this study analyses the Hekkebrugstraat landslide, the best‐recorded landslide in the Flemish Ardennes (Belgium). Information obtained from local inhabitants, aerial photographs and newspaper articles enabled a 50‐year reconstruction of both the landslide history and the land‐use changes at or close to the landslide site. The reconstruction suggests that anthropogenic preliminary factors such as: (i) the absence of well‐maintained drainage ditches in the affected area; (ii) the elevation of the surface of the road, i.e. a sunken lane, in the affected area; (iii) increased surface runoff from the drainage area; (iv) the creation of ponds; and (v) the removal of the lateral support at the landslide foot have played an important role in the reactivation of the Hekkebrugstraat landslide. After the reactivation of February 1995, landslide movement was observed for more than 5 years and caused damage to houses, and other infrastructure. However, also natural factors, such as the presence of an impermeable clay layer at limited depth, springs and relatively steep slopes (i.e. 0.14 m m^?1), and above normal antecedent rainfall have contributed to the reactivations. Comparison of our reconstruction of the reactivation with precise Digital Terrain Models (DTMs) of 1952, 1973 and 1996, produced by digital stereophotogrammetry, indicated that the reported movements correspond well with the uplifted and collapsed zones found on the DTMs. Hence, this analysis provides valuable information for land‐use planners in areas with old, apparently stable, landslides.     

How to save a landrace from extinction: the example of a winter squash landrace (Cucurbita maxima Duchesne) in Northern Italy (Lungavilla-Pavia)

Genetic Resources and Crop Evolution - The present work shows the results of a seven-year project aimed at rescuing the winter squash (Cucurbita maxima Duchesne) landrace ‘Berrettina di...     

O2-enhanced induction of photosynthesis in rice leaves: the Mehler-ascorbate peroxidase (MAP) pathway drives cyclic electron flow within PSII and cyclic electron flow around PSI

Lowering the oxygen (O₂) partial pressure from 21?kPa to 1?kPa delayed the light-dependent increase of the net carbon dioxide (CO₂) assimilation rate in rice (Oryza sativa L. cv. Notohikari) leaves. Researching the underlying molecular mechanisms that act before the start of photosynthesis, we established the following facts. First, O₂ at 21?kPa enhanced the quantum yield of PSII [Y(II)] and PSI [Y(I)]. More than 90% of Y(II) and Y(I) were not accounted for by O₂-dependent electron flow in the Mehler-ascorbate peroxidase (MAP) pathway. Both yields increased further with the start of photosynthesis. Second, O₂ enhanced photochemical quenching of chlorophyll (Chl) fluorescence (qL). qL also increased further with the rate of photosynthesis. Third, O₂ enhanced the photo-oxidation of P700. Fourth, O₂ suppressed the reduction of P700. Fifth, O₂ enhanced non-photochemical quenching of Chl fluorescence (NPQ). These results showed that the MAP pathway triggered cyclic electron flow within PSII (CEF-II) and cyclic electron flow around PSI (CEF-I) by inducing ΔpH across thylakoid membranes and oxidizing the plastoquinone pool, before photosynthesis started. We propose that the photosynthetic electron transport system is controlled by the MAP pathway, which would explain the O₂-dependent enhancement of the induction of photosynthesis.     

Pyrolysis of lignin in the presence of tetramethylammonium hydroxide (TMAH): products stemming from beta-5 substructures

Lignin model compounds, synthetic lignins, and cedar wood have been analyzed by pyrolysis-gas chromatography(-mass spectrometry) in the presence of tetramethylammonium hydroxide (TMAH) to examine the behavior of beta-5 substructures specifically under these conditions. Two model compounds contained a beta-5 linkage and a gamma-CH2OH group. The phenolic model compound produced stilbene products by way of a formaldehyde elimination of the gamma-CH2OH. The nonphenolic model compound underwent dehydration to give arylbenzofuran products. Dehydrogenation polymers of coniferyl alcohol gave a large amount of stilbene products in TMAH/pyrolysis. TMAH/pyrolysis of a Japanese cedar (Cryptomeria japonica) wood yielded a very small amount of stilbene products. The results demonstrated that synthetic lignins are rich in terminal beta-5 substructures, but cedar (a softwood) contains a paucity of the terminal beta-5 substructures.     

Biochar from Different Carbonaceous Waste Materials: Ecotoxicity and Effectiveness in the Sorption of Metal(loid)s

In this study, biochar produced by pyrolysis of urban pruning wood (Bpw) and sewage sludge (Bss) were characterized and investigated as adsorbents for the removal of Cu(II), Pb(II), Zn(II), and As(V) from contaminated solutions. Both types of biochars showed different physical-chemical properties and metal(loid) content. In Bss, Cu, Zn, and Pb concentrations exceeded the upper limit of the common ranges in soils. However, when they were tested for their effect on soil invertebrates, neither of the biochar was expected to exert negative effects as long as the dose applied as an amendment was ≤?4.8 t ha^?1. For an assessment of the effectiveness of biochar in the immobilization of metal(loid)s, three contaminated solutions with acidic pH and different pollutant concentrations were added to both types of biochar. Precipitation as oxy-hydroxides and the formation of complexes with active functional groups of the organic matter were the main mechanisms of metal(loid) fixation by the biochar, with increased precipitation and a rising pH. Both types of biochar were effective at immobilizing Pb and Cu, while Zn showed less effectiveness in this regard and As the least. The high P content of the biochar from sewage sludge favored Pb fixation, presumably forming complexes with phosphates, while competition between phosphate and arsenate ions decreased As adsorption by Fe compounds. The metal(loid)s immobilized by biochar from urban pruning wood were more bioavailable than those fixed by biochar from sewage sludge.