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1.
Urine deposition by grazing livestock causes an immediate increase in nitrous oxide (N2O) emissions, but the responsible mechanisms are not well understood. A nitrogen-15 (15N) labelling study was conducted in an organic grass-clover sward to examine the initial effect of urine on the rates and N2O loss ratio of nitrification (i.e. moles of N2O-N produced per moles of nitrate produced) and denitrification (i.e. moles of N2O produced per moles of N2O+N2 produced). The effect of artificial urine (52.9 g N m−2) and ammonium solution (52.9 g N m−2) was examined in separate experiments at 45% and 35% water-filled pore space (WFPS), respectively, and in each experiment a water control was included. The N2O loss derived from nitrification or denitrification was determined in the field immediately after application of 15N-labelled solutions. During the next 24 h, gross nitrification rates were measured in the field, whereas the denitrification rates were measured in soil cores in the laboratory. Compared with the water control, urine application increased the N2O emission from 3.9 to 42.3 μg N2O-N m−2 h−1, whereas application of ammonium increased the emission from 0.9 to 6.1 μg N2O-N m−2 h−1. In the urine-affected soil, nitrification and denitrification contributed equally to the N2O emission, and the increased N2O loss resulted from a combination of higher rates and higher N2O loss ratios of the processes. In the present study, an enhanced nitrification rate seemed to be the most important factor explaining the high initial N2O emission from urine patches deposited on well-aerated soils.  相似文献   

2.
Agricultural soils contribute significantly to atmospheric nitrous oxide (N2O). A considerable part of the annual N2O emission may occur during the cold season, possibly supported by high product ratios in denitrification (N2O/(N2+N2O)) and nitrification (N2O-N/(NO3−-N+NO2−-N)) at low temperatures and/or in response to freeze-thaw perturbation. Water-soluble organic materials released from frost-sensitive catch crops and green manure may further increase winter emissions. We conducted short-term laboratory incubations under standardized moisture and oxygen (O2) conditions, using nitrogen (N) tracers (15N) to determine process rates and sources of emitted N2O after freeze-thaw treatment of soil or after addition of freeze-thaw extract from clover. Soil respiration and N2O production was stimulated by freeze-thaw or addition of plant extract. The N2O emission response was inversely related to O2 concentration, indicating denitrification as the quantitatively prevailing process. Denitrification product ratios in the two studied soils (pH 4.5 and 7.0) remained largely unaltered by freeze-thaw or freeze-thaw-released plant material, refuting the hypothesis that high winter emissions are due to frost damage of N2O reductase activity. Nitrification rates estimated by nitrate (NO3−) pool enrichment were 1.5-1.8 μg NO3-N g−1 dw soil d−1 in freeze-thaw-treated soil when incubated at O2 concentrations above 2.3 vol% and one order of magnitude lower at 0.8 vol% O2. Thus, the experiments captured a situation with severely O2-limited nitrification. As expected, the O2 stress at 0.8 vol% resulted in a high nitrification product ratio (0.3 g g−1). Despite this high product ratio, only 4.4% of the measured N2O accumulation originated from nitrification, reaffirming that denitrification was the main N2O source at the various tested O2 concentrations in freeze-thaw-affected soil. N2O emission response to both freeze-thaw and plant extract addition appeared strongly linked to stimulation of carbon (C) respiration, suggesting that freeze-thaw-induced release of decomposable organic C was the major driving force for N2O emissions in our soils, both by fuelling denitrifiers and by depleting O2. The soluble C (applied as plant extract) necessary to induce a CO2 and N2O production rate comparable with that of freeze-thaw was 20-30 μg C g−1 soil dw. This is in the range of estimates for over-winter soluble C loss from catch crops and green manure plots reported in the literature. Thus, freeze-thaw-released organic C from plants may play a significant role in freeze-thaw-related N2O emissions.  相似文献   

3.
Soil compaction and soil moisture are important factors influencing denitrification and N2O emission from fertilized soils. We analyzed the combined effects of these factors on the emission of N2O, N2 and CO2 from undisturbed soil cores fertilized with (150 kg N ha−1) in a laboratory experiment. The soil cores were collected from differently compacted areas in a potato field, i.e. the ridges (ρD=1.03 g cm−3), the interrow area (ρD=1.24 g cm−3), and the tractor compacted interrow area (ρD=1.64 g cm−3), and adjusted to constant soil moisture levels between 40 and 98% water-filled pore space (WFPS).High N2O emissions were a result of denitrification and occurred at a WFPS≥70% in all compaction treatments. N2 production occurred only at the highest soil moisture level (≥90% WFPS) but it was considerably smaller than the N2O-N emission in most cases. There was no soil moisture effect on CO2 emission from the differently compacted soils with the exception of the highest soil moisture level (98% WFPS) of the tractor-compacted soil in which soil respiration was significantly reduced. The maximum N2O emission rates from all treatments occurred after rewetting of dry soil. This rewetting effect increased with the amount of water added. The results show the importance of increased carbon availability and associated respiratory O2 consumption induced by soil drying and rewetting for the emissions of N2O.  相似文献   

4.
Stable 15N isotope dilution and tracer techniques were used in cultivated (C) and uncultivated (U) ephemeral wetlands in central Saskatchewan, Canada to: (1) quantify gross mineralization and nitrification rates and (2) estimate the relative proportion of N2O emissions from these wetlands that could be attributed to denitrification versus nitrification-related processes. In-field incubation experiments were repeated in early May, mid-June and late July. Mean gross mineralization and nitrification rates (10.3 and 3.1 mg kg−1 d−1, respectively) did not differ between C and U wetlands on any given date. Despite these similarities, the mean NH4+ pool size in the U wetlands (17.2 mg kg−1) was two to three times that of the C wetlands (6.7 mg kg−1) whereas the mean NO3− pool size in U wetlands (2.2 mg kg−1) was less than half that of C wetlands (5.8 mg kg−1). Mean N2O emissions from the C wetlands decreased from 112.8 to 17.0 ng N2O m2 s−1 from May to July, whereas mean U-wetland N2O emissions ranged only from 31.8 to 51.1 ng N2O m2 s−1 over the same period. This trend is correlated to water-filled pore space in C wetlands, demonstrating a soil moisture influence on emissions. Denitrification is generally considered the dominant emitter of N2O under anaerobic conditions, but in the C wetlands, only 49% of the May emissions could be directly attributed to denitrification, decreasing to 29% in July. In contrast, more than 75% of the N2O emissions from the U wetlands arose from denitrification of the soil NO3− pool throughout the season. These land use differences in emission sources and rates should be taken into consideration when planning management strategies for greenhouse gas mitigation.  相似文献   

5.
Hippuric acid (HA) in cattle urine acts as a natural inhibitor of soil N2O emissions. As HA concentration varies with diet, we determined critical HA levels. We also tested the hypothesis that the inhibition occurs because the HA breakdown product benzoic acid (BA) inhibits denitrification rates. During a 64-day incubation, we quantified emissions from artificial urine varying in HA, BA and glycine (Gly) concentrations, added to a sandy pasture soil. Increasing HA concentration from 0.4 to 5.6 mmol kg−1 soil significantly decreased the average N2O flux by 54%. At 3.9 mmol kg−1 soil, denitrification levels were 50% reduced for BA as compared to Gly. We conclude that HA inhibits both denitrification and N2O emission, at least partly through a BA mechanism.  相似文献   

6.
A laboratory investigation was performed to compare the fluxes of dinitrogen (N2), N2O and carbon dioxide (CO2) from no-till (NT) and conventional till (CT) soils under the same water, mineral nitrogen and temperature status. Intact soil cores (0-10 cm) were incubated for 2 weeks at 25 °C at either 75% or 60% water-filled pore space (WFPS) with 15N-labeled fertilizers (100 mg N kg−1 soil). Gas and soil samples were collected at 1-4 day intervals during the incubation period. The N2O and CO2 fluxes were measured by a gas chromatography (GC) system while total N2 and N2O losses and their 15N mole fractions in the soil mineral N pool were determined by a mass spectrometer. The daily accumulative fluxes of N2 and N2O were significantly affected by tillage, N source and soil moisture. We observed higher (P<0.05) fluxes of N2+N2O, N2O and CO2 from the NT soils than from the CT soils. Compared with the addition of nitrate (NO3−), the addition of ammonium (NH4+) enhanced the emissions of these N and C gases in the CT and NT soils, but the effect of NH4+ on the N2 and/or N2O fluxes was evident only at 60% WFPS, indicating that nitrification and subsequent denitrification contributed largely to the gaseous N losses and N2O emission under the lower moisture condition. Total and fertilizer-induced emissions of N2 and/or N2O were higher (P<0.05) at 75% WFPS than with 60% WFPS, while CO2 fluxes were not influenced by the two moisture levels. These laboratory results indicate that there is greater potential for N2O loss from NT soils than CT soils. Avoiding wet soil conditions (>60% WFPS) and applying a NO3− form of N fertilizer would reduce potential N2O emissions from arable soils.  相似文献   

7.
Earthworm activity has been reported to lead to increased production of the greenhouse gas nitrous oxide (N2O). This is due to emissions from worms themselves, their casts and drilosphere, as well as to general changes in soil structure. However, it remains to be determined how important this effect is on N2O fluxes from agricultural systems under realistic conditions in terms of earthworm density, soil moisture, tillage activity and residue loads. We quantified the effect of earthworm presence on N2O emissions from a pasture after simulated ploughing of the sod (‘grassland renovation’) for different soil moisture contents during a 62-day mesocosm study. Sod (with associated soil) and topsoil were separately collected from a loamy Typic Fluvaquent. Treatments included low (L), medium (M) and high (H) moisture content, in combination with: only soil (S); soil+incorporated sod (SG); soil+incorporated sod+the anecic earthworm Aporrectodea longa (SGE). Nitrous oxide and carbon dioxide (CO2) fluxes were measured for 62 d. At the end of the incubation period, we determined N2O production under water-saturated conditions, potential denitrification and potential mineralization of the soil after removing the earthworms. Cumulative N2O and CO2 fluxes over 62 d from incorporated sod were highest for treatment HSGE (973 μg N2O-N and 302 mg CO2-C kg−1 soil) and lowest for LSG (64 μg N2O-N and 188 mg CO2-C kg−1 soil). Both cumulative fluxes were significantly different for soil moisture (p<0.001), but not for earthworm presence. However, we observed highly significant earthworm effects on N2O fluxes that reversed over time for the H treatments. During the first phase (day 3-day 12), earthworm presence increased N2O emissions with approximately 30%. After a transitional phase, earthworm presence resulted in consistently lower (approximately 50%) emissions from day 44 onwards. Emissions from earthworms themselves were negligible compared to overall soil fluxes. After 62 d, original soil moisture significantly affected potential denitrification, with highest fluxes from the L treatments, and no significant earthworm effect. We conclude that after grassland ploughing, anecic earthworm presence may ultimately lead to lower N2O emissions after an initial phase of elevated emissions. However, the earthworm effect was both determined and exceeded by soil moisture conditions. The observed effects of earthworm activity on N2O emissions were due to the effect of earthworms on soil structure rather than to emissions from the worms themselves.  相似文献   

8.
Earthworm activity may have an effect on nitrous oxide (N2O) emissions from crop residue. However, the importance of this effect and its main controlling variables are largely unknown. The main objective of this study was to determine under which conditions and to what extent earthworm activity impacts N2O emissions from grass residue. For this purpose we initiated a 90-day (experiment I) and a 50-day (experiment II) laboratory mesocosm experiment using a Typic Fluvaquent pasture soil with silt loam texture. In all treatments, residue was applied, and emissions of N2O and carbon dioxide (CO2) were measured. In experiment I the residue was applied on top of the soil surface and we tested (a) the effects of the anecic earthworm species Aporrectodea longa (Ude) vs. the epigeic species Lumbricus rubellus (Hoffmeister) and (b) interactions between earthworm activity and bulk density (1.06 vs. 1.61 g cm−3). In experiment II we tested the effect of L. rubellus after residue was artificially incorporated in the soil. In experiment I, N2O emissions in the presence of earthworms significantly increased from 55.7 to 789.1 μg N2O-N kg−1 soil (L. rubellus; p<0.001) or to 227.2 μg N2O-N kg−1 soil (A. longa; p<0.05). This effect was not dependent on bulk density. However, if the residue was incorporated into the soil (experiment II) the earthworm effect disappeared and emissions were higher (1064.2 μg N2O-N kg−1 soil). At the end of the experiment and after removal of earthworms, a drying/wetting and freezing/thawing cycle resulted in significantly higher emissions of N2O and CO2 from soil with prior presence of L. rubellus. Soil with prior presence of L. rubellus also had higher potential denitrification. We conclude that the main effect of earthworm activity on N2O emissions is through mixing residue into the soil, switching residue decomposition from an aerobic and low denitrification pathway to one with significant denitrification and N2O production. Furthermore, A. longa activity resulted in more stable soil organic matter than L. rubellus.  相似文献   

9.
Urine patches in grazed pastures are a major source of nitrous oxide (N2O) emission. It is well-documented that the relative concentration of the various nitrogenous urine constituents varies significantly with diet. The effect of these variations on N2O emissions from urine patches, however, has never been reported. The aim of this study was to test whether variations in urine composition, consistent with different diets, lead to significant differences in N2O emission. Four varieties of artificial urine, all with similar total N concentrations, but varying in the relative contribution of the nitrogenous constituents, were applied to undisturbed cores from a sandy pasture soil. N2O fluxes were monitored for 65 days at two moisture treatments; 92% WFPS for the entire incubation, and 70% WFPS up to day 41 and 92% afterwards. Extra replicates were included for destructive analysis on mineral N concentrations and pH. Urine composition was a significant (P<0.001) factor determining N2O emissions. An increase in the relative hippuric acid concentration from 3 to 9% of total N resulted in a significant decline in average N2O fluxes, from 16.4 to 8.7 μg N2O-N h−1 kg−1 soil (averaged over all treatments). Cumulative emission decreased from 8.4 to 4.4% of the applied urine-N (P<0.01). Soil mineral N showed a modest but significant decrease with an increase of hippuric acid content. pH did not show any significant relationship with urine composition. Increasing the urea concentration with 12% of applied urinary N did not significantly affect N2O emissions. Moisture content significantly affected N2O emissions (P<0.001), but no interaction between moisture and urine composition was found. As the inhibitory effect of hippuric acid could not be linked directly to mineral N concentrations in the soil, we hypothesize that the breakdown product benzoic acid either inhibits denitrification or decreases the N2O/N2 ratio. We conclude that hippuric acid concentration in urine is an important factor influencing N2O emission, with a potential for reducing emissions with 50%. We suggest alternative rationing leading to higher hippuric acid concentrations in urine as a possible strategy to mitigate N2O emission from grazed pastures.  相似文献   

10.
Nitrous oxide emitted by soils can be produced either by denitrification in anoxic conditions or by nitrification in presence of O2. The relative importance of the two processes, particularly under varied partial pressures of O2, is not always known. This paper focuses on the influence of O2 concentration on N2O production by nitrification and denitrification in an arable Orthic Luvisol. Soil aggregates (2-3 mm size), water unsaturated, received 116 mg N kg−1 as ammonium sulphate labelled with 15N and were incubated during 14 days at different O2 partial pressures: 0, 0.35, 0.76, 1.5, 4.3 and 20.4 kPa. A 15N tracing technique was used to quantify nitrification and denitrification rates. 15N2O and 15N2 were measured. Oxygen pressure appeared to strongly influence both nitrification and denitrification rates and also N2O emissions. Nitrification rates were reduced by a factor of 6-9 when O2 decreased from 20.4 to 0.35 kPa. They were highly correlated with O2 consumption rates. Denitrification mainly occurred in complete anoxic conditions. The proportion of N2O emitted by denitrification was estimated by two independent methods: one based on 15N tracing using isotope composition of NH4, NO3 and N2O, the other based on the measurement of the 15N2O:15N2 ratio. The two methods gave close results. The highest N2O emissions were obtained under complete anoxic conditions and were due to denitrification. However, N2O emissions almost as important were obtained at day 14 with 1.5 kPa O2 pressure, and they were due to nitrification. Nitrification was the main source of N2O at O2 concentrations greater than 0.35 kPa. The amounts of N2O-N emitted by nitrification were linearly related to the amounts of N nitrified, but the slope of the regression was highly dependent on O2 concentration: it varied from 0.16 to 1.48% when O2 concentration was reduced from 20.4 to 0.76 kPa. Emissions of N2O by nitrification may then be quite significant if nitrification occurs at a reduced O2 concentration.  相似文献   

11.
The contribution of nitrification to the emission of nitrous oxide (N2O) from soils may be large, but its regulation is not well understood. The soil pH appears to play a central role for controlling N2O emissions from soil, partly by affecting the N2O product ratios of both denitrification (N2O/(N2+N2O)) and nitrification (N2O/(NO2−+NO3−). Mechanisms responsible for apparently high N2O product ratios of nitrification in acid soils are uncertain. We have investigated the pH regulation of the N2O product ratio of nitrification in a series of experiments with slurries of soils from long-term liming experiments, spanning a pH range from 4.1 to 7.8. 15N labelled nitrate (NO3−) was added to assess nitrification rates by pool dilution and to distinguish between N2O from NO3− reduction and NH3 oxidation. Sterilized soil slurries were used to determine the rates of chemodenitrification (i.e. the production of nitric oxide (NO) and N2O from the chemical decomposition of nitrite (NO2−)) as a function of NO2− concentrations. Additions of NO2− to aerobic soil slurries (with 15N labelled NO3− added) were used to assess its potential for inducing denitrification at aerobic conditions. For soils with pH?5, we found that the N2O product ratios for nitrification were low (0.2-0.9‰) and comparable to values found in pure cultures of ammonia-oxidizing bacteria. In mineral soils we found only a minor increase in the N2O product ratio with increasing soil pH, but the effect was so weak that it justifies a constant N2O product ratio of nitrification for N2O emission models. For the soils with pH 4.1 and 4.2, the apparent N2O product ratio of nitrification was 2 orders of magnitude higher than above pH 5 (76‰ and 14‰). This could partly be accounted for by the rates of chemodenitrification of NO2−. We further found convincing evidence for NO2−-induction of aerobic denitrification in acid soils. The study underlines the role of NO2−, both for regulating denitrification and for the apparent nitrifier-derived N2O emission.  相似文献   

12.
Previous laboratory studies using epigeic and anecic earthworms have shown that earthworm activity can considerably increase nitrous oxide (N2O) emissions from crop residues in soils. However, the universality of this effect across earthworm functional groups and its underlying mechanisms remain unclear. The aims of this study were (i) to determine whether earthworms with an endogeic strategy also affect N2O emissions; (ii) to quantify possible interactions with epigeic earthworms; and (iii) to link these effects to earthworm-induced differences in selected soil properties. We initiated a 90-day 15N-tracer mesocosm study with the endogeic earthworm species Aporrectodea caliginosa (Savigny) and the epigeic species Lumbricus rubellus (Hoffmeister). 15N-labeled radish (Raphanus sativus cv. Adagio L.) residue was placed on top or incorporated into the loamy (Fluvaquent) soil. When residue was incorporated, only A. caliginosa significantly (p < 0.01) increased cumulative N2O emissions from 1350 to 2223 μg N2O-N kg−1 soil, with a corresponding increase in the turnover rate of macroaggregates. When residue was applied on top, L. rubellus significantly (p < 0.001) increased emissions from 524 to 929 μg N2O-N kg−1, and a significant (p < 0.05) interaction between the two earthworm species increased emissions to 1397 μg N2O-N kg−1. These effects coincided with an 84% increase in incorporation of residue 15N into the microaggregate fraction by A. caliginosa (p = 0.003) and an 85% increase in incorporation into the macroaggregate fraction by L. rubellus (p = 0.018). Cumulative CO2 fluxes were only significantly increased by earthworm activity (from 473.9 to 593.6 mg CO2-C kg−1 soil; p = 0.037) in the presence of L. rubellus when residue was applied on top. We conclude that earthworm-induced N2O emissions reflect earthworm feeding strategies: epigeic earthworms can increase N2O emissions when residue is applied on top; endogeic earthworms when residue is incorporated into the soil by humans (tillage) or by other earthworm species. The effects of residue placement and earthworm addition are accompanied by changes in aggregate and SOM turnover, possibly controlling carbon, nitrogen and oxygen availability and therefore denitrification. Our results contribute to understanding the important but intricate relations between (functional) soil biodiversity and the soil greenhouse gas balance. Further research should focus on elucidating the links between the observed changes in soil aggregation and controls on denitrification, including the microbial community.  相似文献   

13.
Initial effects of elevated atmospheric CO2 concentration on N2O fluxes and biomass production of timothy/red clover were studied in the laboratory. The experimental design consisted of two levels of atmospheric CO2 (ca. 360 and 720 μmol CO2 mol−1) and two N fertilisation levels (5 and 10 g N m−2). There was a total of 36 mesocosms comprising sandy loam soil, which were equally distributed in four thermo-controlled greenhouses. In two of the greenhouses, the CO2 concentration was kept at ambient concentration and in the other two at doubled concentration. Forage was harvested and the plants fertilised three times during the basic experiment, followed by harvest, a fertilisation with the double amount of nitrogen and rise of water level. Under elevated CO2, harvestable and total aboveground dry biomass production of a mixed Trifolium/Phleum stand was increased at both N treatments compared to ambient CO2. The N2O flux rates under ambient CO2 were significantly higher at both N treatments during the early growth of mixed Phleum/Trifolium mesocosms compared to the N2O flux rate under elevated CO2. However, when the conditions were favourable for denitrification at the end of the experiment, i.e. N availability and soil moisture were high enough, the elevated CO2 concentration enhanced the N2O efflux.  相似文献   

14.
硝化反应是土壤、特别是干旱半干旱地区农业土壤N2O产生的重要途径之一。但是,目前环境条件对硝化反应中N2O排放的影响研究较少,而在国内外通用的几个模型中均用固定比例估算硝化反应过程中N2O的排放。本文通过砂壤土培养试验,研究了土壤温度、水分和NH4+-N浓度对硝化反应速度及硝化反应中N2O排放的影响,并用数学模型定量表示了各因素对硝化反应的作用,用最小二乘法最优拟合求得该土壤的最大硝化反应速度及N2O最大排放比例。结果表明,随着温度升高,硝化反应速度呈指数增长;水分含量由20%充水孔隙度(WFPS)增加到40%WFPS时,反应速度增加,水分含量增加到60%WFPS时反应速度略有降低;NH4+-N浓度增加对硝化反应速度起抑制作用。用米氏方程描述该土壤的硝化反应过程,其最大硝化反应速度为6.67mg·kg?1·d?1。硝化反应中N2O排放比例随温度升高而降低;随NH4+-N浓度增加而略有增加;20%和40%WFPS水分含量时,硝化反应中N2O排放比例为0.43%～1.50%,最小二乘法求得的最大比例为3.03%,60%WFPS时可能由于反硝化作用,N2O排放比例急剧增加,还需进一步研究水分对硝化反应中N2O排放的影响。  相似文献   

15.
To understand nitrous oxide (N2O) emissions from terrestrial ecosystems it is necessary to understand the processes leading to N2O production. Here, for the first time, results are presented which identify in situ the processes of N2O production in a temperate grassland soil. A small portion of the nitrogen (N) applied in the summer to the grassland soil was rapidly transported below the main rooting zone (>20 cm) and resulted in large N2O productions at depths of 20-50 cm. Preferential pathways must have been responsible for this movement because the soil conditions were not conducive to leaching by piston flow. The N2O was entirely produced by nitrate (NO3−) reduction which was surprising because the bulk soil was aerobic. Therefore, reduction processes can operate during times of the year when it is least expected and cause large N2O concentrations deep in the soil profile.  相似文献   

16.
生物质炭在温室气体减排方面具有很大的发展前景,它不仅能实现固碳,对于在大气中停留时间长且增温潜势大的N2O也能发挥积极作用。本研究采用室内厌氧培养试验,按照生物质炭与土壤质量比（0、1%和5%）加入一定量生物质炭,土壤重量含水率控制在20%。利用Robotized Incubation平台实时检测N2O和N2浓度变化,通过测定土壤中反硝化功能基因丰度（nirK、nirS、nosZ）分析生物质炭对N2O消耗的影响及其微生物方面的影响机理。结果表明：经过20 h厌氧培养后,0生物质炭处理的反硝化功能基因丰度（基因拷贝数·g-1）分别为6.80×107（nirK）、5.59×108（nirS）和1.22×108（nosZ）。与0生物质炭处理相比,1%生物质炭处理的nirS基因丰度由最初的2.65×108基因拷贝数·g-1升至7.43×108基因拷贝数·g-1,nosZ基因丰度则提高了一个数量级,由4.82×107基因拷贝数·g-1升至1.50×108基因拷贝数·g-1,然而nirK基因丰度并无明显变化;5%生物质炭处理的反硝化功能基因丰度并未发生显著变化。试验结束时,添加生物质炭处理的N2/（N2O+N2）比值也明显高于0生物质炭处理。相关性分析结果表明,nirS基因丰度和nosZ基因丰度均与N2O浓度在0.01水平上显著相关。试验末期nirS基因丰度和nosZ基因丰度均随着N2O浓度的降低而升高。因此在本试验中,添加1%生物质炭可显著提高nirS和nosZ基因型反硝化细菌的丰度,增大N2/（N2O+N2）比值,促进N2O彻底还原成N2。生物质炭对于N2O主要影响机理是增大了可以还原氧化亚氮的细菌活性,促进完全反硝化。  相似文献   

17.
Global change scenarios predict an increasing frequency and duration of summer drought periods in Central Europe especially for higher elevation areas. Our current knowledge about the effects of soil drought on nitrogen trace gas fluxes from temperate forest soils is scarce. In this study, the effects of experimentally induced drought on soil N2O and NO emissions were investigated in a mature Norway spruce forest in the Fichtelgebirge (northeastern Bavaria, Germany) in two consecutive years. Drought was induced by roof constructions over a period of 46 days. The experiment was run in three replicates and three non-manipulated plots served as controls. Additionally to the N2O and NO flux measurements in weekly to monthly intervals, soil gas samples from six different soil depths were analysed in time series for N2O concentration as well as isotope abundances to investigate N2O dynamics within the soil. N2O fluxes from soil to the atmosphere at the experimental plots decreased gradually during the drought period from 0.2 to −0.0 μmol m−2 h−1, respectively, and mean cumulative N2O emissions from the manipulated plots were reduced by 43% during experimental drought compared to the controls in 2007. N2O concentration as well as isotope abundance analysis along the soil profiles revealed that a major part of the soil acted as a net sink for N2O, even during drought. This N2O sink, together with diminished N2O production in the organic layers, resulted in successively decreased N2O fluxes during drought, and may even turn this forest soil into a net sink of atmospheric N2O as observed in the first year of the experiment. Enhanced N2O fluxes observed after rewetting up to 0.1 μmol m−2 h−1 were not able to compensate for the preceding drought effect. During the experiment in 2006, with soil matric potentials in 20 cm depth down to −630 hPa, cumulative NO emissions from the throughfall exclusion plots were reduced by 69% compared to the controls, whereas cumulative NO emissions from the experimental plots in 2007, with minimum soil matric potentials of −210 hPa, were 180% of those of the controls. Following wetting, the soil of the throughfall exclusion plots showed significantly larger NO fluxes compared to the controls (up to 9 μmol m−2 h−1 versus 2 μmol m−2 h−1). These fluxes were responsible for 44% of the total emission of NO throughout the whole course of the experiment. NO emissions from this forest soil usually exceeded N2O emissions by one order of magnitude or more except during wintertime.  相似文献   

18.
Estimates of long-term landscape-scale N2O emissions for greenhouse gas inventories are complicated by large temporal and spatial variability. Much of this variability is likely caused by topographic effects on surface and subsurface water flows. We hypothesized that this variability could be explained as degassing events during anaerobic soil conditions and during transitions from anaerobic to aerobic soil conditions as controlled by precipitation and subsequent water redistribution in complex landscapes. We simulated degassing events in the ecosystem model ecosys run in three-dimensional mode to simulate a fertilized agricultural field with topographic variation derived from a digital terrain map. N2O emissions modelled from two areas within the field that had received 15.5 and 9.9 g N m−2 as urea in May 1998 were compared with those measured by micrometeorological flux towers during June and July 1998. Modelled N2O emissions during 1998 accounted for 2.3 and 2.0% of urea N applied at 15.5 and 9.9 g N m−2, respectively. Degassing events in the model coincided with a key N2O emission event measured in the field during several days after a rainfall in mid-June. During this event, modelled and measured surface fluxes rose rapidly to exceed 1 mg N m−2 h−1 for 2-3 d before declining. Emissions modelled concurrently at different topographic positions within the landscape during the emission event had coefficients of variation that varied over time between 30 and 180%. Much of the spatial variability in modelled emissions was attributed to temporal differences in the progression of emission events at different landscape positions caused by lateral water movement. The magnitude of temporal and spatial variability in N2O emissions suggests that aggregation of flux measurements to regional scales should be based upon sub-daily measurements at representative landscape positions, rather than upon less frequent measurements at individual sites as currently done. The use of three-dimensional ecosystem models with input from digital terrain maps may provide a means for such aggregation to be conducted.  相似文献   

19.
Denitrification assays in soils spiked with zinc salt have shown inhibition of the N2O reduction resulting in increased soil N2O fluxes with increasing soil Zn concentration. It is unclear if the same is true for environmentally contaminated soils. Net production of N2O and N2 was monitored during anaerobic incubations (25 °C, He atmosphere) of soils freshly spiked with ZnCl2 and of corresponding soils that were gradually enriched with metals (mainly Zn) in the field by previous sludge amendments or by corrosion of galvanized structures. Total denitrification activity (i.e. the sum of N2O+N2 production rate) was not inhibited by freshly added Zn salts up to 1600 mg Zn kg−1, whereas N2O reduction decreased by 50% (EC50) at total Zn concentrations of 231 mg Zn kg−1 (ZEV soil) and 368 mg Zn kg−1 (TM soil). In contrast, N2O reduction was not reduced by soil Zn in any of the field contaminated soils, even at total soil Zn or soil solution Zn concentrations exceeding more than 5 times corresponding EC50's of the freshly spiked soil. The absence of adverse effects in the field contaminated soils was unrelated to soil NO3 or organic matter concentration. Ageing (2-8 weeks) and soil leaching after spiking reduced the toxicity of Zn on N2O reduction, either expressed as total Zn or soil solution Zn, suggesting adaptation reactions. However, no full recovery after spiking was identified at the largest incubation period in one soil. In addition, the denitrification assay performed with sewage sludge showed elevated N2O release in Zn contaminated sludges (>6000 mg Zn kg−1 dry matter) whereas this was not observed in low Zn sludge (<1000 mg Zn kg−1 dry matter) suggesting limits to adaptation reactions in the sludge particles. It is concluded that the use of soils spiked with Zn salts overestimates effects on N2O reduction. Field data on N2O fluxes in sludge amended soils are required to identify if metals indeed promote N2O emissions in sludge amended soils.  相似文献   

20.
Reduction of nitrous oxide (N2O) to dinitrogen (N2) by denitrification in soils is of outstanding ecological significance since it is the prevailing natural process converting reactive nitrogen back into inert molecular dinitrogen. Furthermore, the extent to which N2O is reduced to N2 via denitrification is a major regulating factor affecting the magnitude of N2O emission from soils. However, due to methodological problems in the past, extremely little information is available on N2 emission and the N2:N2O emission ratio for soils of terrestrial ecosystems. In this study, we simultaneously determined N2 and N2O emissions from intact soil cores taken from a mountainous beech forest ecosystem. The soil cores were taken from plots with distinct differences in microclimate (warm-dry versus cool-moist) and silvicultural treatment (untreated control versus heavy thinning). Due to different microclimates, the plots showed pronounced differences in pH values (range: 6.3–7.3). N2O emission from the soil cores was generally very low (2.0 ± 0.5–6.3 ± 3.8 μg N m−2 h−1 at the warm-dry site and 7.1 ± 3.1–57.4 ± 28.5 μg N m−2 h−1 at the cool-moist site), thus confirming results from field measurements. However, N2 emission exceeded N2O emission by a factor of 21 ± 6–220 ± 122 at the investigated plots. This illustrates that the dominant end product of denitrification at our plots and under the given environmental conditions is N2 rather than N2O. N2 emission showed a huge variability (range: 161 ± 64–1070 ± 499 μg N m−2 h−1), so that potential effects of microclimate or silvicultural treatment on N2 emission could not be identified with certainty. However, there was a significant effect of microclimate on the magnitude of N2O emission as well as on the mean N2:N2O emission ratio. N2:N2O emission ratios were higher and N2O emissions were lower for soil cores taken from the plots with warm-dry microclimate as compared to soil cores taken from the cool-moist microclimate plots. We hypothesize that the increase in the N2:N2O emission ratio at the warm-dry site was due to higher N2O reductase activity provoked by the higher soil pH value of this site. Overall, the results of this study show that the N2:N2O emission ratio is crucial for understanding the regulation of N2O fluxes of the investigated soil and that reliable estimates of N2 emissions are an indispensable prerequisite for accurately calculating total N gas budgets for the investigated ecosystem and very likely for many other terrestrial upland ecosystems as well.  相似文献   

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