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61.
Perspectives on measurement of denitrification in the field including recommended protocols for acetylene based methods 总被引:7,自引:1,他引:6
Of the biogeochemical processes, denitrification has perhaps been the most difficult to study in the field because of the inability to measure the product of the process. The last decade of research, however, has provided both acetylene and15N based methods as well as undisturbed soil core andin situ soil cover sampling approaches to implementing these methods. All of these methods, if used appropriately, give comparable results. Thus, we now have several methods, each with advantages for particular sites or objectives, that accurately measure denitrification in nature. Because of the general usefulness of the acetylene methods, updated protocols for the following three methods are given: gas-phase recirculation soil cores; static soil cores; and the denitrifying enzyme assay also known as the phase 1 assay. Despite the availability of these and other methods, denitrification budgets remain difficult to accurately establish in most environments because of the high spatial and temporal variability inherent in denitrification. Appropriate analysis of those data includes a distribution analysis of the data, and if highly skewed as is typically the case, the most accurate method to estimate the mean and the population variance is the UMVUE method (uniformly minimum variance unbiased estimator). Geostatistical methods have also been employed to improve spatial and temporal estimates of denitrification. These have occasionally been successful for spatial analysis but in the attempt described here for temporal analysis the approach was not useful.Discussions of the importance of denitrification have always focused on quantifying the process and whether particular measured quantities are judged to be a significant amount of nitrogen. A second line of evidence discussed here is the extant genetic record that results from natural selection. These analysis lead to the conclusion that strong selection for denitrification must currently be occurring, which implies that the process is of general significance in soils. 相似文献
62.
Modeling long-term crop response to fertilizer and soil nitrogen 总被引:1,自引:1,他引:0
A simple nitrogen balance model to calculate long-term changes in soil organic nitrogen, nitrogen uptake by the crop and recovery
of applied nitrogen, is presented. It functions with time intervals of one year or one growing season. In the model a labile
and a stable pool of soil organic nitrogen are distinguished. Transfer coefficients for the various inputs of nitrogen are
established that specify the fractions taken up by the crop, lost from the system, and incorporated in soil organic nitrogen.
It is shown how input data, model parameters and initial pool sizes can be derived and how the model can be used for calculating
long-term changes in total soil organic nitrogen and uptake by the crop. For nitrogen applied annually as fertilizer or organic
material the time course of nitrogen uptake and recovery of applied nitrogen is calculated. To test the sensitivity of the
model, calculations have been performed for different environmental conditions with higher or lower risks for losses. The
model has also been applied to establish fertilizer recommendations for a certain target nitrogen uptake by the crop. Finally,
for agricultural systems where periods of cropping alternate with peroids of green fallow the time course of nitrogen uptake
by the crop is calculated. 相似文献
63.
Hajime Tokuda 《Journal of bioenergetics and biomembranes》1989,21(6):693-704
The marine bacteriumVibrio alginolyticus was found to possess the respiratory Na+ pump that generates an electrochemical potential of Na+, which plays a central role in bioenergetics ofV. alginolyticus, as a direct result of respiration. Mutants defective in the Na+ pump revealed that one of the two kinds of NADH: quinone oxidoreductase requires Na+ for activity and functions as the Na+ pump. The Na+ pump composed of three subunits was purified and reconstituted into liposomes. Generation of membrane potential by the reconstituted proteoliposomes required Na+. The respiratory Na+ pump coupled to the NADH: quinone oxidoreductase was found in wide varieties of Gramnegative marine bacteria belonging to the generaAlcaligenes, Alteromonas, andVibrio, and showed a striking similarity in the mode of electron transfer and enzymic properties. Na+ extrusion seemed to be coupled to a dismutation reaction, which leads to the formation of quinol and quinone from semi-quinone radical. 相似文献
64.
The pH of weak-acid solutions is controlled by acid concentration (HA + A–), the degree of acid dissociation (A–/HA), and the strength of the acids present (pKa). We developed an empirical approach that allows the relative importance of each of these factors to be estimated for soils. This empirical model was applied to soils collected from an old-field plantation of loblolly pine (Pinus taeda L.) at 5 and 25 years of age. During this period, soil pH dropped by 0.3 to 0.8 units, and extractable calcium, magnesium and potassium declined by 20 to 80%. The empirical model indicates that the decline in pH resulted largely from the reduction in base saturation of the exchange complex. However, the average acid strength of the exchange complex decreased during the 20 years, preventing a greater decline of perhaps 0.1 to 0.2 units in the observed pH. The rate of decrease in the acid neutralizing capacity to pH 3.5 was about 1.3 kmolc/ha annually, while the increase in base neutralizing capacity was about 2.7 and 1.6 kmolc/ha annually to pH 5.5 and 8.2, respectively. Extractable alkali and alkaline earth cations declined by about 2.2 kmolc/ha annually, matched by the rate of increase in aluminium. These changes demonstrated the dynamic nature of poorly buffered soils, and indicated that changes in soil acidity may be expected over a period of decades (especially following changes in land-use). 相似文献
65.
Soil N mineralization and nitrification in relation to nitrogen solution chemistry in a small forested watershed 总被引:6,自引:1,他引:5
Spatial variations in soil processes regulating mineral N losses to streams were studied in a small watershed near Toronto, Ontario. Annual net N mineralization in the 0–8 cm soil was measured in adjacent upland and riparian forest stands using in situ soil incubations from April 1985 to 1987. Mean annual rates of soil N mineralization and nitrification were higher in a maple soil (93.8 and 87.0 kg.ha–1) than in a pine soil (23.3 and 8.2 kg.ha–1 ). Very low mean rates of mineralization (3.3 kg.ha–1) and nitrification (3.4 kg.ha–1) were found in a riparian hemlock stand. Average NO3-N concentrations in soil solutions were 0.3–1.0 mg.L–1 in the maple stand and >0.06mg.L–1 in the pine stand. Concentrations of NO3–N in shallow ground water and stream water were 3–4× greater in a maple subwatershed than in a pine subwatershed. Rapid N uptake by vegetation was an important mechanism reducing solution losses of NO3–N in the maple stand. Low rates of nitrification were mainly responsible for negligible NO3–N solution losses in the pine stand. 相似文献
66.
Christiane Wloczyk Achim Kröger Thomas Göbel Gabriele Holdt Ralf Steudel 《Archives of microbiology》1989,152(6):600-605
Wolinella succinogenes grown on formate and elemental sulphur was found to use the polysulphide derivatives 2,2-tetrathiobispropionate (R2S4) or pentathionate (S5O
6
=
) as acceptors for formate oxidation. The specific activities of formate oxidation with these acceptors were similar to those with elemental sulphur. The main reaction products of R2S4 reduction were 2,2-dithiobispropionate (R2S2) and sulphide. Pentathionate was converted to thiosulphate and some elemental sulphur. The electrochemical proton potential
across the cytoplasmic membrane of the bacterium was measured in the steady state of electron transport from formate to R2S4. The electrical proportion () of the
determined through the distribution of labeled tetraphenylphosphonium cation was obtained as 0.17 Volt. The was zero, when a protonophore was present. The pH-difference across the membrane was negligible. Thus the
generated by sulphur respiration is close to that measured earlier with fumarate as the terminal acceptor of electron transport.Abbreviations DMO
5,5-dimethyloxazolidine-2,4-dione
- R2Sn (n=2–5)
2,2-polythiobispropionate
- TTFB
4,5,6,7-tetrachloro-2-trifluoromethylbenzimidazol
- TPP
tetraphenylphosphonium cation 相似文献
67.
Rolf Bergmann 《Antonie van Leeuwenhoek》1989,55(2):143-152
Thiolutin was found to inhibit the utilization of glucose and other growth substrates in Escherichia coli. The inhibition was detected by a sharp drop of the respiration rate after addition of the antibiotic. The actual function affected was allocated to the cytoplasmic membrane of the bacterial cells by the following evidence:
It was concluded that the transport of certain substrates across the membrane was inhibited. 相似文献
| - spheroplasts were affected like intact cells, |
| - individual reactions of either the electron transport chain or the glycolytic pathway were not inhibited, |
| - glucose consumption in the culture stopped and the cells accumulated guanosine tetraphosphate as under starvation conditions, |
| - activation of the cell's apo-glucose dehydrogenase restored respiration via bypassing the glucose phosphotransferase system. |
68.
Various components of the Microbial loop such as bacteria, heterotrophic nanoflagellates and autotrophic picoplankton were analyzed, for the first time across the Great Lakes, during a cruise in the summer of 1988. In addition, the size fractionated primary productivity using carbon-14 techniques was also determined. The statistical analysis indicated that bacteria, autotrophic picoplankton and ultraplankton/picoplankton productivity were significantly higher in Lakes Ontario and Erie than Lakes Huron and Michigan. The autotrophic picoplankton and ultraplankton/picoplankton productivity was higher in Lake Erie compared to Lake Ontario.The autotrophic picoplankton showed sensitivity to nutrients and contaminants in various types of environments. A dramatic decrease of autotrophic picoplankton in eutrophic-contaminated areas, such as Ashbridges Bay, Hamilton Harbour and western Lake Erie was observed. Conversely, in Saginaw Bay, another eutrophic environment, the autotrophic picoplankton were significantly higher than in Lake Huron. The sensitivity of autotrophic picoplankton to nutrients/contaminants might have implications to trophic interactions. Our results suggest that structural and functional characteristics of the microbial loop may be operating differently in stressed versus unstressed ecosystems. The possibility of using autotrophic picoplankton as an early warning indicator of environmental perturbation is proposed. 相似文献
69.
Glass-beads (diam. = 250 μm) were buried 10 cm deep in the sediment of a stream. After an exposure of eight weeks, bacterial
densities on the beads varied between 2.7 × 105 and 2.4 × 107/cm2, and the length of the fungal mycelium between 0.2 and 5.3 mm/cm2. Bacterial densities did not show any correlation with the DOC content of the water, but were positively correlated with
respiration on the beads. Fungal mycelium was negatively correlated with water temperature. Acid hydrolysis of stream-exposed
beads released sugars and amino acids, whose combined carbon content exceeded that of the microbial cells by a factor of at
least 4. Gut extracts of Gammarus tigrinus and Tipula caloptera released amino acids and sugars from stream-exposed beads. 相似文献
70.
Functional zooplankton bioassays based on ingestion, reproduction and respiration are described, with methods for a new ingestion bioassay included. All bioassays are compared using three indices, including the variability of controls, the range of experimental responses, and a listing of contaminants causing inhibition/stimulation of response. The ingestion bioassay showed the greatest range of response, and was sensitive to pesticides, PCBs and heavy metals. It was also commonly characterized by a hormesis response. The reproduction bioassay showed the lowest variability, illustrated a reduced range of response, and was sensitive to nutrients and heavy metals. In one study, the respiration bioassay was sensitive only to PCBs. 相似文献