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1.
Carbon (C) sequestration potential of biochar should be considered together with emission of greenhouse gases when applied to soils. In this study, we investigated CO 2 and N 2O emissions following the application of rice husk biochars to cultivated grassland soils and related gas emissions tos oil C and nitrogen (N) dynamics. Treatments included biochar addition (CHAR, NO CHAR) and amendment (COMPOST, UREA, NO FERT). The biochar application rate was 0.3% by weight. The temporal pattern of CO 2 emissions differed according to biochar addition and amendments. CO 2 emissions from the COMPOST soils were significantly higher than those from the UREA and NO FERT soils and less CO 2 emission was observed when biochar and compost were applied together during the summer. Overall N 2O emission was significantly influenced by the interaction between biochar and amendments. In UREA soil, biochar addition increased N 2O emission by 49% compared to the control, while in the COMPOST and NO FERT soils, biochar did not have an effect on N 2O emission. Two possible mechanisms were proposed to explain the higher N 2O emissions upon biochar addition to UREA soil than other soils. Labile C in the biochar may have stimulated microbial N mineralization in the C-limited soil used in our study, resulting in an increase in N 2O emission. Biochar may also have provided the soil with the ability to retain mineral N, leading to increased N 2O emission. The overall results imply that biochar addition can increase C sequestration when applied together with compost, and might stimulate N 2O emission when applied to soil amended with urea. 相似文献
3.
The effect of photosynthesis on N 2O emission from soil was investigated by shading soybean ( Gycline max. L) plant at flowering, pod-setting and grain-filling stages. The results showed that by stopping photosynthesis through
shading the plants stimulated N 2O emission significantly at flowering stage and pod-setting stage, and suppressed N 2O emission dramatically at grain-filling stage. At flowering stage, soybean species seem to rely mainly on fertilizer N and
shaded plants decreased the N uptake. Interaction between the relative increase in available N for N 2O production by shading and the presence of root exudates promoted N transformation (nitrification/denitrification) and N 2O emission. At pod-setting stage, the available soil nitrogen seems to be a critical limiting factor and without substantial
release of symbiotically fixed N through plant roots, resulted in a weak effect of shading on N 2O emission. At grain-filling stage, available N for N 2O production was derived from symbiotically fixed N and was greatly affected by photosynthesis. These results indicated that
the effect of soybean growth on N 2O emission from soil varies with plant growth stages as available N for N 2O production is mainly from fertilizer N and organic mineralization during the early growth of soybean plants, while N 2O emission is controlled by the quantity and perhaps also the quality of root exudates, which is closely related with plant
photosynthesis in the late season of soybean growth. 相似文献
5.
Nitrogen (N) deposition has increased significantly globally since the industrial revolution. Previous studies on the response of gaseous emissions to N deposition have shown controversial results, pointing to the system-specific effect of N addition. Here we conducted an N addition experiment in a temperate natural forest in northeastern China to test how potential changes in N deposition alter soil N 2O emission and its sources from nitrification and denitrification. Soil N 2O emission was measured using closed chamber method and a separate incubation experiment using acetylene inhibition method was carried out to determine denitrification fluxes and the contribution of nitrification and denitrification to N 2O emissions between Jul. and Oct. 2012. An NH 4NO 3 addition of 50 kg N/ha/yr significantly increased N 2O and N 2 emissions, but their “pulse emission” induced by N addition only lasted for two weeks. Mean nitrification-derived N 2O to denitrification-derived N 2O ratio was 0.56 in control plots, indicating higher contribution of denitrification to N 2O emissions in the study area, and this ratio was not influenced by N addition. The N 2O to (N 2+N 2O) ratio was 0.41–0.55 in control plots and was reduced by N addition at one sampling time point. Based on this short term experiment, we propose that N 2O and denitrification rate might increase with increasing N deposition at least by the same fold in the future, which would deteriorate global warming problems. 相似文献
6.
Organic soils are an important source of N 2O, but global estimates of these fluxes remain uncertain because measurements are sparse. We tested the hypothesis that N 2O fluxes can be predicted from estimates of mineral nitrogen input, calculated from readily-available measurements of CO 2 flux and soil C/N ratio. From studies of organic soils throughout the world, we compiled a data set of annual CO 2 and N 2O fluxes which were measured concurrently. The input of soil mineral nitrogen in these studies was estimated from applied fertilizer nitrogen and organic nitrogen mineralization. The latter was calculated by dividing the rate of soil heterotrophic respiration by soil C/N ratio. This index of mineral nitrogen input explained up to 69% of the overall variability of N 2O fluxes, whereas CO 2 flux or soil C/N ratio alone explained only 49% and 36% of the variability, respectively. Including water table level in the model, along with mineral nitrogen input, further improved the model with the explanatory proportion of variability in N 2O flux increasing to 75%. Unlike grassland or cropland soils, forest soils were evidently nitrogen-limited, so water table level had no significant effect on N 2O flux. Our proposed approach, which uses the product of soil-derived CO 2 flux and the inverse of soil C/N ratio as a proxy for nitrogen mineralization, shows promise for estimating regional or global N 2O fluxes from organic soils, although some further enhancements may be warranted. 相似文献
7.
The ocean is a net source of N 2O, a potent greenhouse gas and ozone-depleting agent. However, the removal of N 2O via microbial N 2O consumption is poorly constrained and rate measurements have been restricted to anoxic waters. Here we expand N 2O consumption measurements from anoxic zones to the sharp oxygen gradient above them, and experimentally determine kinetic parameters in both oxic and anoxic seawater for the first time. We find that the substrate affinity, O 2 tolerance, and community composition of N 2O-consuming microbes in oxic waters differ from those in the underlying anoxic layers. Kinetic parameters determined here are used to model in situ N 2O production and consumption rates. Estimated in situ rates differ from measured rates, confirming the necessity to consider kinetics when predicting N 2O cycling. Microbes from the oxic layer consume N 2O under anoxic conditions at a much faster rate than microbes from anoxic zones. These experimental results are in keeping with model results which indicate that N 2O consumption likely takes place above the oxygen deficient zone (ODZ). Thus, the dynamic layer with steep O 2 and N 2O gradients right above the ODZ is a previously ignored potential gatekeeper of N 2O and should be accounted for in the marine N 2O budget.Subject terms: Water microbiology, Biogeochemistry, Microbial ecology 相似文献
8.
Spatial variability in hydrological flowpaths and nitrate-removal processes complicates the overall assessment of riparian
buffer zone functioning in terms of water quality improvement as well as enhancement of the greenhouse effect by N 2O emissions. In this study, we evaluated denitrification and nitrous oxide emission in winter and summer along two groundwater
flowpaths in a nitrate-loaded forested riparian buffer zone and related the variability in these processes to controlling
soil factors. Denitrification and emissions of N 2O were measured using flux chambers and incubation experiments. In winter, N 2O emissions were significantly higher (12.4 mg N m −2 d −1) along the flowpath with high nitrate removal compared with the flowpath with low nitrate removal (2.58 mg N m −2 d −1). In summer a reverse pattern was observed, with higher N 2O emissions (13.6 mg N m −2 d −1) from the flowpath with low nitrate-removal efficiencies. Distinct spatial patterns of denitrification and N 2O emission were observed along the high nitrate-removal transect compared to no clear pattern along the low nitrate-removal
transect, where denitrification activity was very low. Results from this study indicate that spots with high nitrate-removal
efficiency also contribute significantly to an increased N 2O emission from riparian zones. Furthermore, we conclude that high variability in N 2O:N 2 ratio and weak relationships with environmental conditions limit the value of this ratio as a proxy to evaluate the environmental
consequences of riparian buffer zones. 相似文献
9.
通过田间小区试验研究了氮肥一次基施对高肥力土壤上冬小麦产量,吸氮量及氮肥利用率的影响,旨在了解高肥力土训上减少基肥氮的可行性,结果表明,高肥力土壤上冬小麦产量对氮肥的反应不明显,而施用氮肥显著增加了冬小麦吸氮量,根据差值法计算结果,当施氮量为75,112.5和150kg/hm^2时冬小麦的氮肥利用率分别为16.0%,14.5%和13.5%,表明多达84%-86.5%以上的基肥氮未被作物吸收利用,氮平衡计算的结果进一步表明,未被当季小麦利用的肥料氮主要以无机氮的形式残留于0-1m土体中,当施氮量分别为75,112.5和150kg/hm2时氮肥的土壤残留率依次为83.3%,46.0%和58.8%,而相应的表观损失率为0.5%,38.9%和19.0%,由此可见,在高肥力土壤上应严格控制基肥氮的用量或不施基肥,否则将造成氮素资源的大量浪费。 相似文献
11.
氧化亚氮(N2O)是一种重要的温室气体,又能破坏臭氧层[1,2]。土壤是大气N2O的主要来源[3],研究结果表明,我国1990年排放的N2O有9236%来自于农田土壤。各种类型稻田N2O-N排放量占化肥施氮量的0031%~048%[4,5],稻... 相似文献
12.
Despite its ecological importance, essential aspects of microbial N2O reduction—such as the effect of O2 availability on the N2O sink capacity of a community—remain unclear. We studied N2O vs. aerobic respiration in a chemostat culture to explore (i) the extent to which simultaneous respiration of N2O and O2 can occur, (ii) the mechanism governing the competition for N2O and O2, and (iii) how the N2O-reducing capacity of a community is affected by dynamic oxic/anoxic shifts such as those that may occur during nitrogen removal in wastewater treatment systems. Despite its prolonged growth and enrichment with N2O as the sole electron acceptor, the culture readily switched to aerobic respiration upon exposure to O2. When supplied simultaneously, N2O reduction to N2 was only detected when the O2 concentration was limiting the respiration rate. The biomass yields per electron accepted during growth on N2O are in agreement with our current knowledge of electron transport chain biochemistry in model denitrifiers like Paracoccus denitrificans. The culture’s affinity constant (KS) for O2 was found to be two orders of magnitude lower than the value for N2O, explaining the preferential use of O2 over N2O under most environmentally relevant conditions. 相似文献
13.
Escherichia coli carrying the entire nif gene cluster from Klebsiella pneumoniae on a multicopy plasmid becomes more O2-resistant in a N-free medium as a result of the integration of the nif gene cluster into the chromosome and the loss of the plasmid (H.Iwahashi and J.Someya, Biochem. Biophys. Res. Comm. 1990, 168: 288–294). Our purpose is to characterize the physiological reason why the strain became O2-resistant by measuring the levels of nif proteins in cells under microaerobic conditions. The O2-resistant strain had a higher amount of NifH and a lower amount of NifL under microaerobic conditions (compared to that under anaerobic conditions), while the parent strain showed the opposite characteristics. Thus, the biochemical mechanism of the O2-resistant strain is attributed to the strain's ability to synthesize and maintain a high amount of NifH and a low amount of NifL under microaerobic conditions. © Rapid Science Ltd. 1998 相似文献
14.
Temperature responses of denitrifying microbes likely play a governing role in the production and consumption of N 2O. We investigated temperature effects on denitrifier communities and their potential to produce N 2O and N 2 by incubating grassland soils collected in multiple seasons at four temperatures with 15N-enriched NO 3 ? for ~24 h. We quantified [N 2O] concentration across time, estimated its production and reduction to N 2, and quantified relative abundance of genes responsible for N 2O production ( cnorB) and reduction ( nosZ). In all seasons, net N 2O production was positively linked to incubation temperature, with highest estimates of net and gross N 2O production in late spring soils. N 2O dynamics were tightly coupled to changes in denitrifier community structure, which occurred on both seasonal and incubation time scales. We observed increases in nosZ abundance with increasing incubation temperature after 24 h, and relatively larger increases in cnorB abundance from winter to late June. The difference between incubation and in situ temperature was a robust predictor of cnorB:nosZ. These data provide convincing evidence that short-term increases in temperature can induce remarkably rapid changes in community structure that increase the potential for reduction of N 2O to N 2, and that seasonal adaptation of denitrifying communities is linked to seasonal changes in potential N 2O production, with warmer seasons linked to large increases in N 2O production potential. This work helps explain observations of high spatial and temporal variation in N 2O effluxes, and highlights the importance of temperature as an influence on denitrification enzyme kinetics, denitrifier physiology and community adaptations, and associated N 2O efflux and reduction. 相似文献
15.
The aim of the present article is to provide a summary of the epigenetic modifications that might occur in children exposed to heavy metals pollutants. It is known that children are more susceptible to environmental pollutants, because their detoxification enzymes are less competent, and this may lead to alterations in chromatin structure or of DNA causing, in turn, epigenetic modifications. Little is currently known about the long-term effects of these changes when occur early in childhood, none-theless there are ethics and practical concerns that make the assessment of DNA modifications difficult to perform in large-scale. 相似文献
16.
Exposure of CD-1 mice to subanesthetic partial pressures of N2O (0.5 atm) or N2 (10-20 atm) for periods up to 14 days results in up to 40% decreases in the mean threshold pressure eliciting type I high-pressure neurological syndrome (HPNS) seizures, and in increases up to 38% in the N2 partial pressure producing anesthesia. For all combinations of preexposure time, N2 partial pressure, as well as identity of the conditioning gas the relations between the convulsion threshold pressure (Pc) and the anesthesia N2 pressure (Pa) appear to be uniquely correlated by the equation Pa = 54.5 - 0.2(Pc - 60)1.2. The potency of N2O with respect to these habituation phenomena is between 28 and 33 times higher than that of N2, depending on the aspects compared. Evidence is presented indicating that after 14 days of habituation the animals have attained between 75 and 85% compensation for the anesthetic as well as the anticonvulsant effects of the conditioning gas. The bearing of the results on the problem of the nature of the antagonism between inert gas narcotic agents and high pressure and on the hypothesis that habituation tends toward restoration of isofluidity (or some analogous normalization process) are discussed. 相似文献
17.
As genomic data for bacteria are unraveled at an increasing speed, there is a need for more efficient and refined techniques to characterize metabolic traits. The regulatory apparatus for denitrification, for instance, has been explored extensively for type strains, but we lack refined observations of how these and wild type denitrifiers respond metabolically to changing environmental conditions. There is a need for new "phenomic" approaches, and the present paper describes one; an automated incubation system for the study of gas kinetics in 15 parallel bacterial cultures. An autosampler with a peristaltic pump takes samples from the headspace, and replaces the sampled gas with He by reversing the pump. The sample flows through the injector of a micro GC (for determination of N(2), O(2), CH(4), CO(2), N(2)O) to the inlet of a chemoluminescence NO analyzer. The linear range for NO is 0.5-10(4) ppmv (CV=2%, detection limit 0.2 ppmv). The gas leakage of N(2) into the system is low and reproducible, allowing the quantification of N(2) production (in flasks with He+O(2) atmosphere) with a detection limit of 150-200 nmol N(2) for a single time increment. The gas loss by each sampling is taken into account, securing mass balance for all gases, thus allowing accurate estimation of electron flows to the various terminal acceptors (O(2), NO(2)(-), NO, N(2)O) throughout the culture's depletion of O(2) and NO(x). We present some experimental results with Agrobacterium tumefaciens, Paracoccus denitrificans and denitrifying communities, demonstrating the system's potential for unraveling contrasting patterns of denitrification gene expression as a function of concentrations of O(2) and NO in the medium. 相似文献
18.
Quantification of harmful nitrous oxide (N(2)O) emissions from soils is essential for mitigation measures. An important N(2)O producing and reducing process in soils is denitrification, which shows deceased rates at low pH. No clear relationship between N(2)O emissions and soil pH has yet been established because also the relative contribution of N(2)O as the denitrification end product decreases with pH. Our aim was to show the net effect of soil pH on N(2)O production and emission. Therefore, experiments were designed to investigate the effects of pH on NO(3)(-) reduction, N(2)O production and reduction and N(2) production in incubations with pH values set between 4 and 7. Furthermore, field measurements of soil pH and N(2)O emissions were carried out. In incubations, NO(3)(-) reduction and N(2) production rates increased with pH and net N(2)O production rate was highest at pH 5. N(2)O reduction to N(2) was halted until NO(3)(-) was depleted at low pH values, resulting in a built up of N(2)O. As a consequence, N(2)O:N(2) production ratio decreased exponentially with pH. N(2)O reduction appeared therefore more important than N(2)O production in explaining net N(2)O production rates. In the field, a negative exponential relationship for soil pH against N(2)O emissions was observed. Soil pH could therefore be used as a predictive tool for average N(2)O emissions in the studied ecosystem. The occurrence of low pH spots may explain N(2)O emission hotspot occurrence. Future studies should focus on the mechanism behind small scale soil pH variability and the effect of manipulating the pH of soils. 相似文献
20.
China is the world's largest producer and consumer of fertilizer N, and decades of overuse has caused nitrate leaching and possibly soil acidification. We hypothesized that this would enhance the soils' propensity to emit N 2O from denitrification by reducing the expression of the enzyme N 2O reductase. We investigated this by standardized oxic/anoxic incubations of soils from five long‐term fertilization experiments in different regions of China. After adjusting the nitrate concentration to 2 mM, we measured oxic respiration (R), potential denitrification (D), substrate‐induced denitrification, and the denitrification product stoichiometry (NO, N 2O, N 2). Soils with a history of high fertilizer N levels had high N 2O/(N 2O+N 2) ratios, but only in those field experiments where soil pH had been lowered by N fertilization. By comparing all soils, we found a strong negative correlation between pH and the N 2O/(N 2O+N 2) product ratio ( r2 = 0.759, P < 0.001). In contrast, the potential denitrification (D) was found to be a linear function of oxic respiration (R), and the ratio D/R was largely unaffected by soil pH. The immediate effect of liming acidified soils was lowered N 2O/(N 2O+N 2) ratios. The results provide evidence that soil pH has a marginal direct effect on potential denitrification, but that it is the master variable controlling the percentage of denitrified N emitted as N 2O. It has been known for long that low pH may result in high N 2O/(N 2O+N 2) product ratios of denitrification, but our documentation of a pervasive pH‐control of this ratio across soil types and management practices is new. The results are in good agreement with new understanding of how pH may interfere with the expression of N 2O reductase. We argue that the management of soil pH should be high on the agenda for mitigating N 2O emissions in the future, particularly for countries where ongoing intensification of plant production is likely to acidify the soils. 相似文献
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