1,721,069 research outputs found
Responses of nitrous oxide, dinitrogen and carbon dioxide production and oxygen consumption to temperature in forest and agricultural light-textured soils determined by model experiment
No full textThe experiment, carried out on a forest and arable light-textured soil, was designed to study the temperature response of autotrophic and heterotrophic N2O production and investigate how the N2O flux relates to soil respiration and O2 consumption. Although N2O production seemed to be stimulated by a temperature increase in both soils, the relationship between production rate and temperature was different in the two soils. This seemed to depend on the different contribution of nitrification and denitrification to the overall N2O flux. In the forest soil, almost all N2O was derived from nitrification, and its production rate rose linearly from 2 °C to 40 °C. A stronger effect of temperature on N2O production was observed in the arable soil, apparently as a result of an incremental contribution of denitrification to the overall N2O flux with rising temperature. The soil respiration rate increased exponentially with temperature and was significantly correlated with N2O production. O2 consumption stimulated denitrification in both soils. In the arable soil, N2O and N2 production increased exponentially with decreasing O2 concentration, though N2O was the main gas produced at any temperature. In the forest soil, only the N2 flux was related exponentially to O2 consumption and it outweighed the rate of N2O production only at >34°C. Thus, it appears that in the forest soil, where nitrification was the main source of N2O, temperature affected the N2O flux less dramatically than in the arable soil, where a temperature increase strongly stimulated N2O production by enhancing favourable conditions for denitrification
Cycloheximide inhibition of peptone-induced nitrate production across a soil moisture gradient
No full textThe antibiotic block technique is used to distinguish between fungal and bacterial induced activity. In the present study, the antibiotic inhibition of peptone-induced NO3- production was tested across a soil moisture gradient. Soil was incubated at 60, 80, 90 and 100% water-filled pore space (WFPS) and as a water slurry. Peptone was used as the substrate and cycloheximide and C2H2 (0.1% v/v) were added to inhibit fungal and autotrophic nitrification, respectively, the latter being considered mainly of bacterial origin. At all moisture contents is more than 80% of NO 3- production was due to autotrophic nitrification. At increasing water contents the percentage of NO3- production inhibited by C2H2 increased, whereas the percentage inhibited by cycloheximide decreased from 26.4% at 60% WFPS to 4.6% in the water slurry, suggesting a different sensitivity of bacterial and fungal nitrification to soil moisture. Although no direct evidence of an alteration in the fungal population was produced in this experiment, data proved that water content influences the result of the test and hence care should be taken when comparing data using different test conditions. © Springer-Verlag 2005
Factors influencing nitrification and denitrification variability in a natural and fire-disturbed Mediterranean shrubland
No full textThe main factors influencing the variability of nitrification and denitrification enzyme activity (DEA), in soil of a Mediterranean shrubland, were investigated in an undisturbed area and in plots treated with experimental fires of two different intensities. Soil was sampled 4 times during 1 year after burning, in periods characterised by different environmental conditions. In the control, net nitrification ranged from 0.95 to 1.32 μg NO3--N g-1 day-1 and did not show significant average differences among sampling events, probably because water content and NH4+-N availability were both limiting the process at any time. Overall, nitrification seemed associated with microsites where NH4+-N production was higher. This pattern was not evident in the burned plots, where, moreover, a partial reduction of activity immediately after burning was observed. DEA showed higher variability among sampling events, as compared with nitrification, with a peak in winter. It also presented a close spatial relationship with microsites of nitrification activity. In the burned sites, water content, organic C and NO3--N content concurred to explain DEA variability together with NH4+-N availability and nitrification activity. Plots treated with intense fire showed the lowest values of DEA, especially in the period more favourable to this activity
Methane production and consumption in an active volcanic environment of Southern Italy
No full textMethane fluxes were measured, using closed chambers, in the Crater of Solfatara volcano, Campi Flegrei (Southern Italy), along eight transects covering areas of the crater presenting different landscape physiognomies. These included open bare areas, presenting high geothermal fluxes, and areas covered by vegetation, which developed along a gradient from the central open area outwards, in the form of maquis, grassland and woodland. Methane fluxes decreased logarithmically (from 150 to -4.5 mg CH 4 m -2 day -1) going from the central part of the crater (fangaia) to the forested edges, similarly to the CO 2 fluxes (from 1500 g CO 2 m -2 day -1in the centre of the crater to almost zero flux in the woodlands). In areas characterized by high emissions, soil presented elevated temperature (up to 70°C at 0-10 cm depth) and extremely low pH (down to 1.8). Conversely, in woodland areas pH was higher (between 3.7 and 5.1) and soil temperature close to air values. Soil (0-10 cm) was sampled, in two different occasions, along the eight transects, and was tested for methane oxidation capacity in laboratory. Areas covered by vegetation mostly consumed CH 4 in the following order woodland > macchia > grassland. Methanotrophic activity was also measured in soil from the open bare area. Oxidation rates were comparable to those measured in the plant covered areas and were significantly correlated with field CH 4 emissions. The biological mechanism of uptake was demonstrated by the absence of activity in autoclaved replicates. Thus results suggest the existence of a population of micro-organisms adapted to this extreme environment, which are able to oxidize CH 4 and whose activity could be stimulated and supported by elevated concentrations of CH 4. © 2004 Elsevier Ltd. All rights reserved
The effect of different N substrates on biological N2O production from forest and agricultural light textured soils
No full textN2O emissions from two slightly alkaline sandy soils, from arable land and a woodland, were determined in a laboratory experiment in which the soils were incubated with different sources of nitrogen, with or without glucose, and with 0, 1 and 100 mL C2H2 L-1. Large differences in the rate of N2O production were observed between the two soils and between the different N treatments. The arable soil showed very low N2O emissions derived from reduced forms of N as compared with the N2O which was produced when the soil was provided with NO2/- or NO3/- and a C source, suggesting a very active denitrifier population. In contrast, the woodland soil showed a very low denitrification activity and a much higher N2O production derived from the oxidation of NH4/+ and reduction of NO2/- by some processes probably mediated by autotrophic or heterotrophic nitrifiers or dissimilatory NO2/- reducers. In both soils, the highest N2O emissions were induced by NO2/- addition. Those emissions were demonstrated to have a biological origin, as no significant N2O emissions were measured when the soil was autoclaved
A GIS based application of the IPCC protocol for the estimation of N2O emissions from agricultural ecosystems of the Italian region
No full textEffect of cycloheximide on N2O and NO3/- production in a forest and an agricultural soil
No full textThe present work aims at evaluating the effect of cycloheximide at concentrations of between 0.5 and 5 mg g-1 on N2O and NO3/- production in two slightly alkaline soils, sampled from deciduous woodland and arable cultivation. In the first experiment, peptone was used as the 'inducing substrate' for heterotrophic activity, and soil was incubated with cycloheximide (at different concentrations) and/or acetylene (1 ml l-1) to block induced eukaryotic protein synthesis and ammonia monooxygenase activity, respectively. Peptone addition stimulated N2O and NO3/- production significantly in woodland soil, whereas arable soil showed no significant N2O emissions and low NO3/- production. Low cycloheximide concentrations drastically reduced N2O emissions in woodland soil, suggesting a potential role of fungi in N2O emissions. However, acetylene was equally effective in blocking N2O emissions and part of NO3/- production, so that a possible role of ammonia monooxygenase in an organic-inorganic pathway of N nitrification in fungal metabolism can be hypothesized. A second experiment was carried out on the woodland soil to check if low cycloheximide concentrations had non-target biocidal effects on soil microorganisms. Attention was focused on the range of concentrations which had reduced N2O emission in the woodland soil. The results suggested that at concentrations of cycloheximide between 0.5 and 2 mg g-1 any biocidal effect on microbial biomass was negligible in the first 48 h; therefore only selective inhibition of protein synthesis could be expected. The whole nitrifier population seemed to be particularly sensitive to cycloheximide concentrations higher than 2.5 mg g-1
Short term effects of burning on soil microbial processes involved in greenhouse gas fluxes from soil
No full textFluxes of N2O and CH4 from soils of savannas and seasonally-dry ecosystems
No full textAim: Savannas and seasonally-dry ecosystems cover a significant part of the world's land surface. If undisturbed, these ecosystems might be expected to show a net uptake of methane (CH4) and a limited emission of nitrous oxide (N2O). Land management has the potential to change dramatically the characteristics and gas exchange of ecosystems. The present work investigates the contribution of warm climate seasonally-dry ecosystems to the atmospheric concentration of nitrous oxide and methane, and analyses the impact of land-use change on N2O and CH4 fluxes from the ecosystems in question. Location: Flux data reviewed here were collected from the literature; they come from savannas and seasonally-dry ecosystems in warm climatic regions, including South America, India, Australasia and Mediterranean areas. Methods: Data on gas fluxes were collected from the literature. Two factors were considered as determinants of the variation in gas fluxes: land management and season. Land management was grouped into: (1) control, (2) 'burned only' and (3) managed ecosystems. The season was categorized as dry or wet. In order to avoid the possibility that the influence of soil properties on gas fluxes might confound any differences caused by land management, sites were grouped in homogeneous clusters on the basis of soil properties, using multivariate analyses. Inter- and intra-cluster analysis of gas fluxes were performed, taking into account the effects of season, land management and main vegetation types. Results: Soils were often acid and nutrient-poor, with low water retention. N2O emissions were generally very low (median flux 0.32 mg N2O m-2 day-1), and no significant differences were observed between woodland savannas and managed savannas. The highest fluxes (up to 12.9 mg N2O m-2 day-1) were those on relatively fertile soils with high air-filled porosity and water retention. The effect of season on N2O production was evident only when sites were separated in homogeneous groups on the basis of soil properties. CH4 fluxes varied over a wide range (-22.9 to 3.15 mg CH4 m-2 day-1, where the negative sign denotes removal of gas from the atmosphere), with an annual average daily flux of -0.48 ± 0.96 (SD) mg CH4 m-2 day-1 in undisturbed (control) sites. Land-use change dramatically reduced this CH4 sink. Managed sites were weak sinks of CH4 in the dry season and became sources of CH4 in the wet season. This was particularly evident for pastures. Burning alone did not reduce soil net CH4 oxidation, but decreased N2O production. Main conclusions: Despite the low potential for N2O production, both in natural and managed conditions, tropical seasonally-dry ecosystems represent a significant source of N2O (4.4 Tg N2O year-1) on a global scale, as a consequence of the large area they occupy. The same environments represent a potential CH 4 sink of 5.17 Tg CH4 year-1. However, assuming that c. 30% of the tropical land is converted to different uses, the sink would be reduced to 3.2 Tg CH4 year-1. The limited information on fluxes from Mediterranean ecosystems does not allow a meaningful scaling up. © 2006 Blackwell Publishing Ltd
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