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Customary methods of stimulating and recording were used to examine threshold shifts of the single visual receptor in the lateral eye of Limulus in response to low-level x-irradiation. Marked visual sensitization was found and was most pronounced at the lowest dosage levels (1 to 25 r). Complete light adaptation apparently cancelled the effects of the irradiation. 相似文献
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A brief burst of x-rays elicited flight activity in moths placed in a darkened x-ray exposure room. Wing-beat activity was recorded as an index of this behavior. Wing-beat activity could be initiated in resting moths or amplitude augmented in active moths by x-ray dose rates of 0.01 to 1.5 roentgens per second, with a latency of less than 1 second after onset of exposure. 相似文献
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THE OCCURRENCE OF ETHYLENE IN ANAEROBIC SOIL 总被引:6,自引:0,他引:6
The production of ethylene and other hydrocarbon gases by soils under anaerobic conditions was measured by gas chromatography. Ethylene was the only hydrocarbon gas which occurred in physiologically significant concentrations; more than 20 ppm was found in several soils after 10 days at 20°C. These concentrations were considerably higher than those which were known to cause severe reductions in the extension of root axes of some plant species. Experiments with sterilized and unsterilized soil indicated that ethylene was produced by enzyme activity and not by chemical action. The gas was found in soil when the oxygen concentration fell below 2 per cent; total evolution was correlated with organic matter content, and was affected by drying and rewetting and by the growth of plant roots. The rate of production was increased by raising the temperature and by addition of glucose or peptone; high concentrations of nitrate depressed the rate, but sulphate and phosphate had little effect. It is concluded that ethylene may be a significant factor in causing injury to crop plants under waterlogged conditions and also in situations where anaerobic pockets occur within a mainly aerobic soil structure, provided that escape of the gas from the soil is impeded sufficiently to allow inhibitory concentrations to build up in the vicinity of plant roots. 相似文献
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Relative gas diffusivity (D/D0 ) was measured in peat cores equilibrated to set moisture tensions between zero and - l0 kPa, using the radioactive gas 85 Kr. A relationship between relative diffusivity and the air filled porosity was obtained, which showed lower values of D/D0 at air-filled porosities above about 0.13m3 m−3 , and higher values at porosities below about 0.10m3 m−3 than some of those found in the literature for mineral soils. The likely effects of shrinkage behaviour on drying in the field, on the relationship between D/D0 and air-filled porosity, are discussed. 相似文献
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A combination of mathematical analysis and computer simulation, using parameters readily measured in a nitrogen-15 field experiment, is employed to determine rates of mineralization, immobilization and nitrification under a growing crop. The procedure also yields the proportion of crop nitrogen uptake occurring as ammonium and nitrate.
When applied to -results from grass lysimeters receiving 250 or 900 kg N ha–1 a–1 as ammonium nitrate, the analysis suggested that at 250 kgN ha–1 a–1 64–66% of crop nitrogen uptake was as ammonium; at 900 kg N ha–1 a–1 the figure was 43–49%. Nitrification at 250kgNha–1 was only 13–19kgN ha–1 over 160d while at 900 kg N ha–1 between 191 and 232 kg N ha–1 were nitrified.
The results suggested that the apparent inhibition of nitrification in grassland soils may simply reflect poor substrate competition by nitrifying bacteria. Finally, there was a suggestion that mineralization/immobilization was lower at the high fertilizer rate. 相似文献
When applied to -results from grass lysimeters receiving 250 or 900 kg N ha
The results suggested that the apparent inhibition of nitrification in grassland soils may simply reflect poor substrate competition by nitrifying bacteria. Finally, there was a suggestion that mineralization/immobilization was lower at the high fertilizer rate. 相似文献