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991.
The Wachsenburg Sandstone of Thuringia (Central Germany) occurs within playa deposits of the Arnstadt Formation (Late Triassic,
Norian) and furnishes an example of ephemeral river metamorphosis under dryland conditions. Characterized by high flow regime
features, the sand-dominated lithofacies constitution exhibits sedimentation by channel processes under the influence of recurring
flash floods. Bearing signatures of subaerial exposures, the fining-upward lithofacies cycles are bound by low-angle lateral
accretion elements suggesting deposition in a meandering stream. Channel migration in response to point bar expansion and
active bank erosion, led to the development of four laterally shifting point bar events. Unimodal palaeocurrent patterns with
low variance and azimuthal dispersion support the point bar origin of the Wachsenburg Sandstone. With reduced water budget
under largely semi-arid climate, the river progressively became smaller, highly sinuous and ultimately abandoned. The resulting
point bar succession was finally covered with sheet flow deposits of over bank origin. The sandstone was deposited during
a period of low base-level when the playa system temporarily fell dry. 相似文献
992.
The effect of denervation on the contractile activity of the saphenous artery in normotensive rats and rats with regional hypotension was studied. Hypotension was caused by partial occlusion of the abdominal aorta distally from the renal arteries, and then, in four weeks, to denervate the saphenous artery, a portion of the femoral nerve in one of the limbs was resected. In two more weeks, the contractile responses of ring preparations of the saphenous artery (after removal of the endothelium and block of neuronal uptake and β-adrenoreceptors) were investigated under isometric conditions. In normotensive rats, the denervation led to an increase in the vascular sensitivity to norepinephrine, phenylephrine, serotonin, and KCl. Similar changes in contraction were caused by chronic hypotension; however, rats with hypotension exhibited no additional denervation-induced increase in the vascular sensitivity. After treatment with glyoxylic acid, the fluorescence intensity of the vascular adrenergic fibers adapted to a reduced pressure was lower than that in the norm. It was assumed that the vascular hypersensitivity in hypotension is caused by impairment of sympathetic innervation. 相似文献
993.
Temperature effects on egg development of the rosy apple aphid and forecasting of egg hatch 总被引:1,自引:0,他引:1
B. Graf H.U. Höpli H. Höhn & J. Samietz 《Entomologia Experimentalis et Applicata》2006,119(3):207-211
The development of Dysaphis plantaginea (Pass.) (Homoptera: Aphididae) winter eggs was studied at six different constant temperatures ranging from 7.5 to 16.5 °C in order to improve the basis for phenological forecasts in early spring. The mortality was generally low at temperatures below 13.5 °C but increased considerably at 16.5 °C. The effect of temperature on development rates could be described with linear regression within the temperature range under study. The lower temperature threshold for development was estimated to be 4.0 °C and the thermal constant 140 day‐degrees. A time‐varying distributed delay approach was used to establish a temperature driven phenology model for winter egg hatch of D. plantaginea considering the intrinsic variability in development time. The model parameters such as temperature‐dependent development times and corresponding variances were quantified based on the experimental data. When compared with independent observations on egg hatch under semifield conditions, the model gave satisfactory validation results. It can be used as forecasting tool for the optimal timing of monitoring and control measures for D. plantaginea in early spring. 相似文献
994.
R. Schwamborn W. Ekau A. P. Silva S. H. L. Schwamborn T. A. Silva S. Neumann-Leitão U. Saint-Paul 《Hydrobiologia》2006,560(1):1-13
Ingestion rates of zoeae of Aratus pisonii Milne Edwards (Brachyura: Grapsidae) were determined offering natural plankton-detritus mixtures in laboratory food selection
experiments. The food mixtures were sampled in the Itamaracá estuary, north-eastern Brazil, and standardised to a size range
of 50–200 μm. Zoeae ingested significant amounts of large centric diatoms (Coscinodiscus spp.), mangrove detritus, tintinnids (Favella ehrenbergi) and adult copepods during feeding experiments. Diatoms were positively selected by A. pisonii zoeae in all three experiments, with ingestion rates of 3.3–21.3 cells zoea−1 day−1. Detritus particles were always more abundant than phytoplankton and zooplankton in the particle size spectrum offered. Detritus
was ingested in two of three experiments, with ingestion rates of up to 34.1 particles zoea−1 day−1, being the most important food item during one experiment. Adult copepods (up to 1.8 ind. zoea−1 day−1) and tintinnids (up to 0.4 ind. zoea−1 day−1) were ingested by A. pisonii zoeae during one experiment each. In spite of a wide range of zoeal density, food particle composition, and density, zoeae
of A. pisonii displayed a consistent pattern of food selectivity. This hints at a consistent sensory and behavioural mechanism related
to capture and handling of food particles, that most likely also affects larval feeding under natural conditions. Although
detritus showed to be quantitatively ingested under estuarine conditions, zoeae of A. pisonii preferred large diatoms and ingested zooplankton only occasionally. 相似文献
995.
U. S. Iskandarov A. G. Guzalova K. D. Davranov 《Applied Biochemistry and Microbiology》2006,42(1):72-76
The effects of nutrient medium composition and temperature on the germination of conidia of the fungi Beauveria bassiana (strain AlG) and Metarhizium anisopliae (strain M-99) and their entomopathogenic activity have been studied. It was demonstrated that the presence of carbohydrates alone was sufficient for the spores of M. anisopliae M-99 to germinate, whereas the germination of B. bassiana AlG spores was inhibited by carbohydrates. Addition of KJ, ZnSO4, or KBr into the Czapek medium increased the entomopathogenic activity of B. bassiana. The optimum temperature for spore germination was 20–35°C in both fungal species. 相似文献
996.
The aphid Astegopteryx sp. forms a banana-bunch shaped gall consisting of several subgalls on Styrax benzoides in northern Thailand, and completes its life cycle on the tree, without migrating to secondary hostplants. We found that
its soldiers had sclerotic, protruded heads with many spine-like setae, and that several soldiers cooperate to plug the ostiole
of the subgall with these heads. Of 173 ostioles examined in the field, 90.8 % were plugged with no space among the guarding
soldiers. Many eggs and sexuals were found within subgalls guarded by soldiers, and a number of males were found trying to
intrude into these subgalls. However, they were blocked by guarding soldiers, and it was no easy task for them to intrude
into subgalls. The same was true for some soldiers that had rushed out of the subgall. Guarding soldiers often prevented outside
soldiers from coming back into the subgall. These findings suggest an interesting possibility that guarding soldiers might
consequently select still active, reusable soldiers and strong males for sexual females in their subgall.
Received 6 March 2005; revised 5 and 20 July 2005; accepted 27 July 2005. 相似文献
997.
U. B. Willi G. N. Bronner P. M. Narins 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2006,192(3):267-277
Comparison between the middle ear anatomy of the Cape golden mole (Chrysochloris asiatica), which exhibits a club-shaped malleus head, and the Desert golden mole (Eremitalpa granti), with a ball-shaped malleus head, suggests differences in sensitivity to airborne sound. Scanning laser Doppler vibrometric
measurements of the ossicular behavior in response to both vibration and airborne sound were made in C. asiatica. Two distinct vibrational modes were observed. In response to low-frequency vibration (70–200 Hz), the malleus oscillates
about the ligament of the short process of the incus, whereas in response to high-frequency airborne sound (1–6 kHz) the ossicular
chain rotates about the long axis of malleus. It is proposed that the club-shaped malleus head in C. asiatica constitutes an adaptation towards bimodal hearing—sensitivity to substrate vibrations and airborne sound. Possible functional
differences between these two middle ear types are discussed. 相似文献
998.
999.
Post-fire nutrient flushes are an important precursor to secondary succession in fire-driven boreal forest. We studied the magnitude of changes in post-fire soil nutrient status across a chronosequence of ericaceous shrub-dominated boreal forest stands in eastern Newfoundland, Canada. The chronosequence comprised nine stands burned between 1 and 38 years prior to the study. These sites have resisted tree reestablishment following forest fire-induced mortality of black spruce and a concomitant increase in dominance of the ericaceous dwarf shrub Kalmia angustifolia L. Our objectives were: (1) to identify the factors driving soil nutrient status in these post-fire stands dominated by ericaceous plants, and (2) to test hypotheses that specific relationships exist among environmental factors, dominant vegetation and indicators of soil nutrient status. Macronutrients such as NH4+, total organic N and mineral soil P concentrations showed non-linear declines with time since fire. These parameters were also negatively associated with cover of ericaceous plants. Potential phytotoxins such as total phenolics and aluminium concentrations increased with increasing cover of K. angustifolia. Variability in net ammonification, total P and total phenolic acids in organic soils were strongly related to ericaceous dominance even when the effect of time since fire was partialled out using regression analysis. These findings suggest a strong capacity for ericaceous vegetation to have top-down effects on soil chemical property particularly in the organic horizon with the increase in its post-fire dominance. 相似文献
1000.
Evaluation of Food Additives and Low-toxicity Compounds for the Control of Bean Rust and Wheat Leaf Rust 总被引:1,自引:0,他引:1
The efficacy of low‐toxicity chemicals as possible alternatives to synthetic fungicides for the control of Uromyces appendiculatus and Puccinia triticina was evaluated. A preliminary selection of food additives was performed through in vitro and in vivo preliminary screenings. The ED50 and minimum inhibition concentration (MIC) values showed that most of the food additives used in this study were more toxic to U. appendiculatus than to P. triticina. Acetic acid, potassium carbonate, sodium carbonate and sodium molybdate were the food additives that were more toxic to the urediniospores of P. triticina. Selected compounds and concentrations were tested on bean and wheat plants grown in pots under controlled conditions. Acetic acid, ammonium bicarbonate, potassium acetate, potassium benzoate, potassium bicarbonate, potassium carbonate, sodium acetate and sodium citrate at 0.03, 0.09, 0.03, 0.006, 0.012, 0.012, 0.03 and 0.03 m , respectively, significantly reduced the disease severity of U. appendiculatus without causing any injury to bean leaves. Ammonium bicarbonate, potassium bicarbonate, sodium bicarbonate and sodium citrate at 0.12, 0.03, 0.12 and 0.03 m , respectively, were the most effective in reducing the disease severity caused by P. triticina without causing any injury to wheat leaves. 相似文献