Sulfur cycling in a dutch moorland pool under elevated atmospheric S-deposition

Atmospheric S deposition, sulfate reduction and the accumulation of reduced S components were investigated in sediments of a Dutch moorland pool. Laboratory ³⁵SO42? tracer experiments indicated that the variation in reduction rate with depth in the sediment could be described by an exponential fit, suggesting first order kinetics. Sulfate reduction rates calculated from a kinetic transport model were highest in June and July (>0.6 mmol m^?2 day^?1), and decreased towards the end of the summer (<0.2 mmol m^?2 day^?1). Winter reduction rates were low, but increased towards the beginning of the spring. Concentrations of total, organic and inorganic S decreased with depth, consistent with an increasing depositional flux of S over the last century. Increased atmospheric sulfate deposition rates and consumption in the upper sedimentary layers caused a continuous increase in subsurface S concentrations. Present day S-immobilization rates were estimated between 25 to 30 mmol S in^?2 yr^?1, in the order of the annual input of S from wet atmospheric deposition. Sulfate metabolism in anaerobic moorland pool sediments may be the most important mechanism of long-term S-accumulation.     

Aluminosilicate phases during initial clay formation: H+-Al3+–oxalic acid–silicic acid–Na+ system

The solid phases and the precipitation boundary characterizing the system H⁺-Al³⁺-oxalic acid-silicic acid-Na⁺ are discussed. Model experiments have been used to throw more light on two environmental problems: the formation of sparingly soluble aluminium silicates in oceans and alkaline lakes, which could be determining aluminium and silicate concentrations in pore waters of sediments, and the validity of inorganic and organic mechanisms of podzolization and their significance for soil science. pH and Tyndallometric measurements were performed at constant ionic strength of 0.6 M NaCl at 25°C. Three phases Al(OH)₄, H₄SiO₄ (phase Vi^a), Al₂, (OH)₆.H₄SiO₄ (phase VI^b) and NaAl(OH)₄.(H₄SiO₄), (phase VIII) determine the precipitation boundary. Phase NaAl(OH)₄.H₄SiO₄ (phase VII precipitates at 0.4pH units above NaAl(OH)₄.(H₄SiO₄)₂. Using a set of previously determined binary and ternary complexes, and phases of the subsystems, the following formation constants were deduced: Phases VI^a and VI^b are described as end-members of the allophane series with Si: Al ratios of 1:1 and 1.2. Phase VI^b was identified with protoimogolite allophane. These two phases are good model clays for podzolic soils and are extremely soluble at pH < 4. Sodium phases could be hydrous feldspathoids. These phases are possible in sediments of seawater or saline lakes. It is suggested that organic and inorganic mechanisms of podzolization operate sequentially and that neither of them alone can completely describe the process.     

Impacts of rising atmospheric carbon dioxide on model terrestrial ecosystems

In model terrestrial ecosystems maintained for three plant generations at elevated concentrations of atmospheric carbon dioxide, increases in photosynthetically fixed carbon were allocated below ground, raising concentrations of dissolved organic carbon in soil. These effects were then transmitted up the decomposer food chain. Soil microbial biomass was unaffected, but the composition of soil fungal species changed, with increases in rates of cellulose decomposition. There were also changes in the abundance and species composition of Collembola, fungal-feeding arthropods. These results have implications for long-term feedback processes in soil ecosystems that are subject to rising global atmospheric carbon dioxide concentrations.     

Spontaneous emission spectrum in double quantum dot devices

A double quantum dot device is a tunable two-level system for electronic energy states. A dc electron current was used to directly measure the rates for elastic and inelastic transitions between the two levels. For inelastic transitions, energy is exchanged with bosonic degrees of freedom in the environment. The inelastic transition rates are well described by the Einstein coefficients, relating absorption with stimulated and spontaneous emission. The most effectively coupled bosons in the specific environment of the semiconductor device used here were acoustic phonons. The experiments demonstrate the importance of vacuum fluctuations in the environment for quantum dot devices and potential design constraints for their use for preparing long-lived quantum states.     

Double-bridge hybrids of Solanum bulbocastanum and cultivars of Solanum tuberosum

Summary Solanum bulbocastanum (2n=2x=24) has valuable characters for potato breeding, but cannot be hybridized directly with S. tuberosum cultivars. Both S. acaule (2n=4x) and S. phureja (2n=2x) were used as bridging species. Triploid S. acaule × S. bulbocastanum were doubled with colchicine and the resulting fertile hexaploid F₁'s crossed with S. phureja. The triple hybrids obtained were tetraploid or nearly so. The two genomes of S. acaule in these triple hybrids probably pair preferentially, which may provoke pairing and possibly crossing over between the chromosomes of S. bulbocastanum and S. phureja.More than 20000 pollinations of the triple hybrids with four potato cultivars had to be made to produce 40 quadruple hybrids. These highly vigorous hybrids varied greatly in many morphological characters, resistance to Phytophthora infestans, fertility and crossability. The chromosome numbers are 48 (24 hybrids), 49 and 46, but some higher ploidy levels (65, 66, 72 chromosomes) were found as well. Their origin is to be sought in the fusion of an unreduced egg cell from triple hybrids (either euploid or hypoploid) and a reduced male gamete from the cultivars. This view is corroborated by their extreme resistance to Phytophthora. Also some 48-chromosome hybrids are highly resistant, which may indicate introgression from S. bulbocastanum.Most quadruple hybrids are readily inter-crossable and crossable as females with cultivars; several also as males. Two could be hybridized with S. bulbocastanum, but the few seeds dit not germinate.Studies of pachytene stage of meiosis revealed the presence of a S. bulbocastanum chromosome in at least one tetraploid hybrid, which is highly resistant to Phytophthora. At metaphase I of meiosis chromosome associations higher than quadrivalents were not found. Except in one hybrid, the frequency of quadrivalents did not exceed one per cell and the average proportion of chromosomes associated as bivalents amounted to 90%.The quadruple hybrids (double-bridge hybrids) appear good starting material for breeding programmes aimed at introducing genes from S. bulbocastanum into S. tuberosum cultivars.     

Comparative Aspects of the Endotoxin- and Cytokine-Induced Endocrine Cascade Influencing Neuroendocrine Control of Growth and Reproduction in Farm Animals

Disease in animals is a well-known inhibitor of growth and reproduction. Earlier studies were initiated to determine the effects of endotoxin on pituitary hormone secretion. These studies found that in sheep, growth hormone (GH) concentration was elevated, whereas insulin-like growth factor-I (IGF-I) was inhibited, as was luteinizing hormone (LH). Examination of the site of action of endotoxin in sheep determined that somatotropes expressed the endotoxin receptor (CD14) and that both endotoxin and interleukin-Iβ activated GH secretion directly from the pituitary. In the face of elevated GH, there is a reduction of IGF-I in all species examined. As GH cannot activate IGF-I release during disease, there appears to be a downregulation of GH signalling at the liver, perhaps related to altered nitration of Janus kinase (JAK). In contrast to GH downregulation, LH release is inhibited at the level of the hypothalamus. New insights have been gained in determining the mechanisms by which disease perturbs growth and reproduction, particularly with regard to nitration of critical control pathways, with this perhaps serving as a novel mechanism central to lipopolysaccharide suppression of all signalling pathways. This pathway-based analysis is critical to the developing novel strategies to reverse the detrimental effect of disease on animal production.     

Occurrence of pepper yellow vein in the Netherlands

Samenvatting Het verschijnsel van geelnervigheid bij paprika (Capsicum annuum) kon door verenting en met de schimmelOlpidium brassicae worden overgebracht. Hierdoor bleek de ziekte identiek te zijn met een eerder in Engeland gemelde ziekte. Door inoculatie met zoösporen of rustsporen vanO. brassicae werden ook symptomen verkregen inC. baccatum, C. chacoense enC. frutescens. S. villosum bleek een waardplant te zijn voor het geelnervigheidsagens, waarbij zwakke nerfchlorosen werden waargenomen.Seconded to the Glasshouse Crops Research Station, P.O. Box 8, 2670 AA Naaldwijk, the Netherlands.