Role Of Denitrification Research Articles

Nitrogen deposition and the forest nitrogen cycle: role of denitrification

The fate and effects of anthropogenic N deposition in forest ecosystems are discussed, and a conceptual hypothesis for the ecosystem response to elevated N deposition is presented. The concept of ‘nitrogen saturation’ is discussed and defined. The interactions of effects of excess N (nutrient deficiencies, loss of mycorrhiza, soil acidification, etc.) are described; these may destabilize the forest ecosystem and contribute to forest decline. Estimates of long-term critical N loads for forest ecosystems of 2–20 kg N ha −1 year −1, depending on biomass utilization are derived from simple mass balance considerations. Denitrification is supposed to be an insignificant process in the N-cycling of most forests. It may not alleviate the impact of deposition inputs, but it may be an important process in relation to atmospheric stability.

Soil Losses of Dinitrogen and Nitrous Oxide from Irrigated Crops in Northeastern Colorado

AbstractEmissions of nitrous oxide (N20) and dinitrogen (N2) from irrigated fields were monitored during the 1982 and 1983 cropping season to assess the magnitude of N loss by denitrification. Miniplots were established within larger fields of corn (Zea mays L.) in 1982, and barley (Hordeum vulgare) in 1983. Soil inside the miniplots was amended at a rate of 200 kg N ha−1 as 99 atom % 15N ammonium sulfate, and the vertical N20 and N2 fluxes were measured periodically by sampling gases from a soil cover method, and analyzing the N20 by gas chromatography and the N2 by mass spectrometry. Maximum N20 emissions occurred in May for barley and in July for corn, and emissions for both crops increased with increasing soil‐water content. During 1982, total volatile N loss of N20 + N2 from the moderately well‐drained clay loam soil was about 2.5% of the applied fertilizer N, and about 70% of the total was N20. From the barley field in 1983, about 1% of the applied fertilizer N was emitted with about equal amounts of each gas. These data suggest that the role of denitrification as a N loss mechanism has been historically overemphasized for soils in this area.

Fate of nitrogen applied to agricultural crops with particular reference to denitrification

The effectiveness of N fertilizer depends on the ability of crops to compete with microorganisms for the available N in the soil. Adverse growth conditions (e.g. drought and waterlogging) diminish the capacity of the plants for N uptake, while N supply may be limited by transient assimilation by microorganisms, by longer-term immobilization into soil hum us and by losses through leaching and denitrification. Conversely, mineralization of soil organic matter contributes to the availability of N. Significant alteration of soil management methods (e.g. improvement of drainage, use of simplifed cultivation systems, or rotation of arable land with grass) may change the balance of processes within the nitrogen cycle. The results of field and lysimeter experiments (some with 15 N-labelled fertilizer) are used to discuss these aspects of the fate of applied N, with particular attention to the role of denitrification.

Mineral transformations by fungi in culture and in soils

Abstract Although micro‐organisms are regarded as the principal agents of mineral cycling in soils, the role of bacteria has generally been emphasized, while that of fungi has been neglected. Fungi are able to transform the majority of elements in vitro but whether they play an important role in soil is as yet unknown. There is sufficient circumstantial evidence from soil studies to suggest that fungi may under certain conditions nitrify and oxidize reduced forms of sulphur. Their role in denitrification and sulphate reduction process is more speculative. While they appear incapable of nitrogen fixation, fungi undoubtedly play a major role in the mineralization of organic N,P, and S in soils, in the solubilization of insoluble phosphates, and participate in oxidation of manganese. Perhaps one of their most important roles is in the dissolution of silica and rocks thus releasing ions into the soil solution during weathering. The ability of fungi to oxidize elements in vitro does not compare with that of the chemoautotrophic bacteria. On the other hand in vitro activity tells us little about the activity of an organism in the soil. At present our appreciation of the part played by fungi in mineral cycling in soils is limited by the techniques available, but there is little doubt that they have a major role to play in the cycling of elements other than carbon.

Denitrification in Lake Kinneret in the presence of oxygen*

SUMMARY. Denitrification experiments under anaerobic and aerated conditions were carried out in the laboratory with Lake Kinneret water and with pure cultures of the denitrifying bacteria Pseudomonas aeruginosa 2 Kin isolated from the lake. Although losses of nitrogen in Lake Kinneret due to denitrification have been found to occur during periods when dissolved oxygen exceeded 5 mg l−1 it was found that under aerated conditions glucose as a carbon source must be added in order to get denitrification in the laboratory.Disappearance of nitrogen during the experiments was due to denitrification as shown by the nitrogen balance calculated for each sampling. The ATP content showed that no proliferation of cells took place during the experiment.The rate of denitrification was strongly influenced by and was directly proportional to nitrate concentrations. Temperature has a very slight effect on the denitrification rate. Q10 for the range 15–30°C was 1.35.The role of denitrification in the nitrogen balance of Lake Kinneret is discussed.