Silicon nutrition of tomato and bitter gourd with special emphasis on silicon distribution in root fractions     

Gregor Heine  George Tikum  Walter J. Horst 《植物养料与土壤学杂志》2005,168(4):600-606

Two plant species, tomato (Lycopersicon esculentum Mill.) and bitter gourd (Momordica charantia), were used for in‐depth studies on the dynamics of silicon (Si) uptake and translocation to the shoots and compartmentation of Si in the roots. The experiments were conducted under controlled environmental conditions in nutrient solutions, which were partly amended with 1 mM Si in the form of silicic acid. At harvest, xylem exudates were collected, and Si concentrations and biomass of roots and shoots were determined. Mass flow of Si was calculated based on the Si concentration of the nutrient solution and transpiration determined in a parallel experiment. Plant roots were subjected to a fractionated Si analysis, allowing attributing Si to different root compartments. Silicon concentrations in the roots compared to the shoots were higher in tomato but lower in bitter gourd. A more ready translocation from the roots to the shoots in bitter gourd was in agreement with Si concentrations in the xylem exudates which were higher than in the external solution. In tomato, the xylem‐sap Si concentration was lower than in the nutrient solution. Calculated Si mass flow to the root exceeded Si uptake in tomato, which was consistent with the measured accumulation of Si in the root water‐free space (WFS). In contrast, Si concentration in the root WFS was lower than in the nutrient solution in bitter gourd, reflecting the calculated Si depletion at the root surface based on the comparison of Si mass flow and Si uptake. Within the roots, more than 80% of the total Si was located in the cell wall and less than 10% in the cytoplasmic fractions in tomato. In bitter gourd, between 60% and 70% of the total root Si was attributed to the cell‐wall fraction whereas the proportion of the cytoplasmic fraction reached more than 30%. Our results clearly confirm that tomato belongs to the Si excluders and bitter gourd to the Si‐accumulator plant species for which high Si concentrations in the cytoplasmic root fraction appear to be characteristic.  相似文献   

Simulation of snowmelt erosion using the EROSION 3D model     

Astrid Weigert  Gerald Wenk  Gregor Ollesch  Heiko Fritz 《植物养料与土壤学杂志》2003,166(1):128-130

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Atmospheric methane and nitrous oxide of the Late Pleistocene from Antarctic ice cores     

Spahni R  Chappellaz J  Stocker TF  Loulergue L  Hausammann G  Kawamura K  Flückiger J  Schwander J  Raynaud D  Masson-Delmotte V  Jouzel J 《Science (New York, N.Y.)》2005,310(5752):1317-1321

The European Project for Ice Coring in Antarctica Dome C ice core enables us to extend existing records of atmospheric methane (CH4) and nitrous oxide (N2O) back to 650,000 years before the present. A combined record of CH4 measured along the Dome C and the Vostok ice cores demonstrates, within the resolution of our measurements, that preindustrial concentrations over Antarctica have not exceeded 773 +/- 15 ppbv (parts per billion by volume) during the past 650,000 years. Before 420,000 years ago, when interglacials were cooler, maximum CH4 concentrations were only about 600 ppbv, similar to lower Holocene values. In contrast, the N2O record shows maximum concentrations of 278 +/- 7 ppbv, slightly higher than early Holocene values.  相似文献   

Island biology and ecosystem functioning in epiphytic soil communities     

Wardle DA  Yeates GW  Barker GM  Bellingham PJ  Bonner KI  Williamson WM 《Science (New York, N.Y.)》2003,301(5640):1717-1720

Although island attributes such as size and accessibility to colonizing organisms can influence community structure, the consequences of these for ecosystem functioning are little understood. A study of the suspended soils of spatially discrete epiphytes or treetop "islands" in the canopies of New Zealand rainforest trees revealed that different components of the decomposer community responded either positively or negatively to island size, as well as to the tree species that the islands occurred in. This in turn led to important differences between islands in the rates of ecosystem processes driven by the decomposer biota. This system serves as a model for better understanding how attributes of both real and habitat islands may affect key ecosystem functions through determining the community structure of organisms that drive these functions.  相似文献   

Conditional dynamics of interacting quantum dots     

Robledo L  Elzerman J  Jundt G  Atatüre M  Högele A  Fält S  Imamoglu A 《Science (New York, N.Y.)》2008,320(5877):772-775

Conditional quantum dynamics, where the quantum state of one system controls the outcome of measurements on another quantum system, is at the heart of quantum information processing. We demonstrate conditional dynamics for two coupled quantum dots, whereby the probability that one quantum dot makes a transition to an optically excited state is controlled by the presence or absence of an optical excitation in the neighboring dot. Interaction between the dots is mediated by the tunnel coupling between optically excited states and can be optically gated by applying a laser field of the right frequency. Our results represent substantial progress toward realization of an optically effected controlled-phase gate between two solid-state qubits.  相似文献   

Condensation of semiconductor microcavity exciton polaritons     

Deng H  Weihs G  Santori C  Bloch J  Yamamoto Y 《Science (New York, N.Y.)》2002,298(5591):199-202

A phase transition from a classical thermal mixed state to a quantum-mechanical pure state of exciton polaritons is observed in a GaAs multiple quantum-well microcavity from the decrease of the second-order coherence function. Supporting evidence is obtained from the observation of a nonlinear threshold behavior in the pump-intensity dependence of the emission, a polariton-like dispersion relation above threshold, and a decrease of the relaxation time into the lower polariton state. The condensation of microcavity exciton polaritons is confirmed.  相似文献   

Glutamatergic and dopaminergic neurons mediate anxiogenic and anxiolytic effects of CRHR1     

Refojo D  Schweizer M  Kuehne C  Ehrenberg S  Thoeringer C  Vogl AM  Dedic N  Schumacher M  von Wolff G  Avrabos C  Touma C  Engblom D  Schütz G  Nave KA  Eder M  Wotjak CT  Sillaber I  Holsboer F  Wurst W  Deussing JM 《Science (New York, N.Y.)》2011,333(6051):1903-1907

The corticotropin-releasing hormone receptor 1 (CRHR1) critically controls behavioral adaptation to stress and is causally linked to emotional disorders. Using neurochemical and genetic tools, we determined that CRHR1 is expressed in forebrain glutamatergic and γ-aminobutyric acid-containing (GABAergic) neurons as well as in midbrain dopaminergic neurons. Via specific CRHR1 deletions in glutamatergic, GABAergic, dopaminergic, and serotonergic cells, we found that the lack of CRHR1 in forebrain glutamatergic circuits reduces anxiety and impairs neurotransmission in the amygdala and hippocampus. Selective deletion of CRHR1 in midbrain dopaminergic neurons increases anxiety-like behavior and reduces dopamine release in the prefrontal cortex. These results define a bidirectional model for the role of CRHR1 in anxiety and suggest that an imbalance between CRHR1-controlled anxiogenic glutamatergic and anxiolytic dopaminergic systems might lead to emotional disorders.  相似文献   

Modelling of snowmelt erosion and sediment yield in a small low-mountain catchment in Germany   总被引：1，自引：0，他引：1  

Gregor Ollesch  Irina Kistner  Ralph Meissner  Karl-Erich Lindenschmidt 《CATENA》2006,68(2-3):161

Temporal variability and spatial heterogeneity of surface runoff generation triggers the dynamics of source areas of sediment and sediment-associated nutrient transport. Reliable modelling of hydrological special situations i.e. snowmelt is of high importance for the quality of erosion and sediment yield modelling. Data from the research catchment Schäfertal demonstrate the individuality of snowmelt events in terms of runoff coefficient and delivery ratio. This 1.44 km² low mountain catchment is characterised by a high portion of arable land with a winter grain/winter rape crop rotation. The integrated winter erosion and nutrient load model (IWAN) considers these dynamic aspects by coupling a hydrological model with a sediment load model. Cell size of this raster-based approach is 10 × 10 m². Additionally, snowmelt rill erosion is simulated with a newly developed physically based model that is firstly applied on a catchment scale. A sensitivity analysis of this model system component demonstrates the plausibility of the model approach and the overall robustness of the model system IWAN. The results of the long-term hydrological modelling from 1991 to 2003 are reliable and form the basis for the simulation of six snowmelt events which were observed in the Schäfertal catchment. The estimated total runoff volumes for these events match the observations well. The modelled overland runoff coefficients vary from 0.001 to 0.72. The mean values of cell erosion, which were modelled with one set of parameters for all six events range from 0.0006 to 0.96 t ha^− 1. The total modelled erosion for the events with unfrozen soil and low amount of surface runoff is of a factor 50 below those with partly frozen soil. In addition to these distinctions, the major differences are caused by flow accumulation in shallow depressions in variable parts of the catchment. However, the validation of these results on the single event scale is restricted due to limited spatial data. Total simulated sediment yield at the catchment outlet was as high as 13.84 t which underestimates the observed values, with the exception of one event. Oversimplification of the modelled channel processes may be a reason. The temporal variability and spatial heterogeneity of the surface roughness parameter, which was identified to be sensitive, also causes uncertainty in the parameter estimation. Despite these findings, the model system IWAN was applied successfully on the catchment scale and the simulated results are reliable.  相似文献   

Testate amoebae as predators of nematodes     

Gregor W. Yeates  Wilhelm Foissner 《Biology and Fertility of Soils》1995,20(1):1-7

Testacea were observed ingesting nematodes in the litter horizons of native forests in New Zealand. Nematodes were most commonly attacked from the tail end but some specimens were attacked at mid-body. Nematodes with damaged tails were recovered in greatest numbers from the highest, wettest site sampled. Nebela (Apodera) vas (Certes, 1989) and Difflugia sp. (possibly lanceolata Penard, 1890) were the predators; both species were redescribed using light and scanning electron microscopy and morphometry. Most damaged nematodes were Ironus sp. but Clarkus, Tobrilus, Iotonchus, Cobbonchus, Dorylaimus and Plectus were also attacked. Literature on testacean feeding strategies was reviewed briefly.  相似文献   

Effect of fertilizers with the new nitrification inhibitor DMPP (3,4-dimethylpyrazole phosphate) on yield and quality of agricultural and horticultural crops   总被引：1，自引：0，他引：1  

Gregor Pasda  Reinhardt Hähndel  Wolfram Zerulla 《Biology and Fertility of Soils》2001,34(2):85-97

In 1997-1999, 136 field trials were conducted under various soil-climatic conditions in western and southern Europe in order to assess the effects of N fertilizers with the new nitrification inhibitor (NI) 3,4-dimethylpyrazole phosphate (DMPP) on the yield and quality of various agricultural and horticultural crops. Results show that DMPP may increase the mean crop yield (grain yield, winter wheat +0.25 t ha^-1, wetland rice +0.29 t ha^-1, grain maize +0.24 t ha^-1; tuber yield, potatoes +1.9 t ha^-1; corrected sugar yield, sugar beets +0.24 t ha^-1; biomass, carrots +4.9 t ha^-1, lambs' lettuce +1.9 t ha^-1, onions +0.5 t ha^-1, radish +4.6 t ha^-1, lettuce +1.4 t ha^-1, cauliflower +5.2 t ha^-1, leek +1.7 t ha^-1, celeriac +2.2 t ha^-1) and/or improve crop quality (e.g. reduced NO₃^- concentration in leafy vegetables). In some crops, the same yield level as obtained with the control (fertilizer without DMPP) was achieved with one fewer applications of N, or with a reduced N application rate. The positive effect of DMPP on crop yield was especially pronounced at sites with a high precipitation rate or intensive irrigation, and/or light sandy soil. DMPP had a negative effect on the crude protein concentration of winter wheat and on the biomass yield of spring-grown spinach.  相似文献