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1.
PurposeBetter understanding of N transformations and the regulation of N2O-related N transformation processes in pasture soil contributes significantly to N fertilizer management and development of targeted mitigation strategies.Materials and methods15N tracer technique combined with acetylene (C2H2) method was used to measure gross N transformation rates and to distinguish pathways of N2O production in two Australian pasture soils. The soils were collected from Glenormiston (GN) and Terang (TR), Victoria, Australia, and incubated at a soil moisture content of 60% water-filled pore space (WFPS) and at temperature of 20 °C.Results and discussionTwo tested pasture soils were characterized by high mineralization and immobilization turnover. The average gross N nitrification rate (ntot) was 7.28 mg N kg?1 day?1 in TR soil () and 5.79 mg N kg?1 day?1 in GN soil. Heterotrophic nitrification rates (nh), which accounting for 50.8 and 41.9% of ntot, and 23.4 and 30.1% of N2O emissions in GN and TR soils, respectively, played a role similar with autotrophic nitrification in total nitrification and N2O emission. Denitrification rates in two pasture soils were as low as 0.003–0.004 mg N kg?1 day?1 under selected conditions but contributed more than 30% of N2O emissions.ConclusionsResults demonstrated that two tested pasture soils were characterized by fast N transformation rates of mineralization, immobilization, and nitrification. Heterotrophic nitrification could be an important NO3?–N production transformation process in studied pasture soils. Except for autotrophic nitrification, roles of heterotrophic nitrification and denitrification in N2O emission in two pasture soils should be considered when developing mitigation strategies. 相似文献
2.
AbstractTo evaluate the hypothesis that plant-mediated oxygen supplies decrease methane (CH 4) production and total global warming potential (GWP) in a tropical peatland, the authors compared the fluxes and dissolved concentrations of greenhouse gases [GHGs; CH 4, carbon dioxide (CO 2) and nitrous oxide (N 2O)] and dissolved oxygen (DO) at multiple peatland ecosystems in Central Kalimantan, Indonesia. Study ecosystems included tropical peat swamp forest and degraded peatland areas that were burned and/or drained during the rainy season. CH 4 fluxes were significantly influenced by land use and drainage, which were highest in the flooded burnt sites (5.75 ± 6.66 mg C m ?2 h ?1) followed by the flooded forest sites (1.37 ± 2.03 mg C m ?2 h ?1), the drained burnt site (0.220 ± 0.143 mg C m ?2 h ?1), and the drained forest site (0.0084 ± 0.0321 mg C m ?2 h ?1). Dissolved CH 4 concentrations were also significantly affected by land use and drainage, which were highest in the flooded burnt sites (124 ± 84 μmol L ?1) followed by the drained burnt site (45.2 ± 29.8 μmol L ?1), the flooded forest sites (1.15 ± 1.38 μmol L ?1) and the drained forest site (0.860 ± 0.819 μmol L ?1). DO concentrations were influenced by land use only, which were significantly higher in the forest sites (6.9 ± 5.6 μmol L ?1) compared to the burnt sites (4.0 ± 2.9 μmol L ?1). These results suggest that CH 4 produced in the peat might be oxidized by plant-mediated oxygen supply in the forest sites. CO 2 fluxes were significantly higher in the drained forest site (340 ± 250 mg C m ?2 h ?1 with a water table level of ?20 to ?60 cm) than in the drained burnt site (108 ± 115 mg C m ?2 h ?1 with a water table level of ?15 to +10 cm). Dissolved CO 2 concentrations were 0.6–3.5 mmol L ?1, also highest in the drained forest site. These results suggested enhanced CO 2 emission by aerobic peat decomposition and plant respiration in the drained forest site. N 2O fluxes ranged from ?2.4 to ?8.7 μg N m ?2 h ?1 in the flooded sites and from 3.4 to 8.1 μg N m ?2 h ?1 in the drained sites. The negative N 2O fluxes might be caused by N 2O consumption by denitrification under flooded conditions. Dissolved N 2O concentrations were 0.005–0.22 μmol L ?1 but occurred at < 0.01 μmol L ?1 in most cases. GWP was mainly determined by CO 2 flux, with the highest levels in the drained forest site. Despite having almost the same CO 2 flux, GWP in the flooded burnt sites was 20% higher than that in the flooded forest sites due to the large CH 4 emission (not significant). N 2O fluxes made little contribution to GWP. 相似文献
3.
Denitrification has long been considered a major mechanism of N loss when N fertilizer is applied to flooded rice paddies. However, the direct determination of denitrification in soils is almost impossible because of the high atmospheric background of dinitrogen (N 2). Dissolved N 2 in a small water sample can be rapidly and precisely measured through membrane inlet mass spectrometry (MIMS). This study is the first to directly measure N 2 flux through MIMS in flooded rice paddy plots that received different amounts of urea. Ammonia (NH 3) volatilization was measured simultaneously to verify whether NH 3 volatilization and denitrification are complementary loss mechanisms. The average cumulative N 2–N loss measured by MIMS 21 days after fertilization was 4.7?±?1.7 % of the applied N, which was within the range of the reported values obtained by cumulative recovery of (N 2 + N 2O)– 15N and 15N-balance technique. Underestimation or overestimation of denitrification can be prevented in MIMS given that N 2 can be measured directly without 15N-labeled fertilizer. A good positive correlation was found between the dissolved in situ N 2 concentrations of floodwater and the denitrification rates of intact soil cores. Urea incorporation reduced NH 3 volatilization unlike surface broadcasting. However, urea incorporation significantly increased cumulative N 2–N loss during the 21 days after fertilization. Correlation analysis showed that nitrate (NO 3 ?–N) concentration in floodwater could be the primary restricting factor for soil denitrification in the experimental field. Results suggest that MIMS is a promising technique for the measurement of denitrification in a flooded rice paddy. 相似文献
4.
Amending vegetable soils with organic materials is increasingly recommended as an agroecosystems management option to improve soil quality. However, the amounts of NO, N 2O, and N 2 emissions from vegetable soils treated with organic materials and frequent irrigation are not known. In laboratory-based experiments, soil from a NO 3 ? -rich (340 mg N?kg ?1) vegetable field was incubated at 30°C for 30 days, with and without 10 % C 2H 2, at 50, 70, or 90 % water-holding capacity (WHC) and was amended at 1.19 g?C kg ?1 (equivalent to 2.5 t?C ha ?1) as Chinese milk vetch (CMV), ryegrass (RG), or wheat straw (WS); a soil not amended with organic material was used as a control (CK). At 50 % WHC, cumulative N 2 production (398–524 μg N?kg ?1) was significantly higher than N 2O (84.6–190 μg N?kg ?1) and NO (196–224 μg N?kg ?1) production, suggesting the occurrence of denitrification under unsaturated conditions. Organic materials and soil water content significantly influenced NO emissions, but the effect was relatively weak since the cumulative NO production ranged from 124 to 261 μg N?kg ?1. At 50–90 % WHC, the added organic materials did not affect the accumulated NO 3 ? in vegetable soil but enhanced N 2O emissions, and the effect was greater by increasing soil water content. At 90 % WHC, N 2O production reached 13,645–45,224 μg N?kg ?1 from soil and could be ranked as RG?>?CMV?>?WS?>?CK. These results suggest the importance of preventing excess water in soil while simultaneously taking into account the quality of organic materials applied to vegetable soils. 相似文献
5.
Nitrous oxide (N 2O) emissions from the soil surface of five different forest types in Thailand were measured using the closed chamber method. Soil samples were also taken to study the N 2O production pathways. The monthly average emissions (±SD, n?=?12) of N 2O from dry evergreen forest (DEF), hill evergreen forest (HEF), moist evergreen forest (MEF), mixed deciduous forest (MDF) and acacia reforestation (ARF) were 13.0?±?8.2, 5.7?±?7.1, 1.2?±?12.1, 7.3?±?8.5 and 16.7?±?9.2?µg N m ?2 h ?1, respectively. Large seasonal variations in fluxes were observed. Emission was relatively higher during the wet season than during the dry season, indicating that soil moisture and denitrification were probably the main controlling factors. Net N 2O uptake was also observed occasionally. Laboratory studies were conducted to further investigate the influence of moisture and the N 2O production pathways. Production rates at 30% water holding capacity (WHC) were 3.9?±?0.2, 0.5?±?0.06 and 0.87?±?0.01?ng N 2O-nitrogen (N) g-dw ?1day ?1 in DEF, HEF and MEF respectively. At 60% WHC, N 2O production rates in DEF, HEF and MEF soils increased by factors of 68, 9 and 502, respectively. Denitrification was found to be the main N 2O production pathway in these soils except in MEF. 相似文献
6.
A better understanding of the nitrogen (N) cycle in agricultural soils is crucial for developing sustainable and environmentally friendly N fertilizer management and to propose effective nitrous oxide (N 2O) mitigation strategies. This laboratory study quantified gross nitrogen transformation rates in uncultivated and cultivated black soils in Northeast China. It also elucidated the contribution made by nitrification and denitrification to the emissions of N 2O. In the laboratory, soil samples adjusted to 60 % water holding capacity (WHC) were spiked with 15NH 4NO 3 and NH 4 15NO 3 and incubated at 25 °C for 7 days. The size and 15N enrichment of the mineral N pools and the N 2O emission rates were determined between 0 and 7 days. The results showed that the average N 2O emission rate was 21.6 ng N 2O-N kg ?1 h ?1 in cultivated soil, significantly higher than in the uncultivated soil (11.6 ng N 2O-N kg ?1 h ?1). Denitrification was found to be responsible for 32.1 % of the N 2O emission in uncultivated soil, and the ratio increased significantly to 43.2 % in cultivated soil, due to the decrease in soil pH. Most of the increase in net N 2O-N emissions observed in the cultivated soil was resulting from the increased production of N 2O through denitrification. Gross nitrification rate was significantly higher in the cultivated soil than in the uncultivated soil, and the ratio of gross nitrification rate/ammonium immobilization rate was 6.87 in cultivated soil, much larger than the uncultivated soil, indicating that nitrification was the dominant NH 4 + consuming process in cultivated soil, and this will lead to the increased production of nitrate, whereas the increased contribution of denitrification to N 2O emission promoted the larger emission of N 2O. This double impact explains why the risk of N loss to the environment is increased by long-term cultivation and fertilization of native prairie sites, and controlling nitrification maybe effective to abate the negative environmental effects. 相似文献
7.
PurposeIncreased sedimentation due to land use intensification is increasingly affecting carbon processing in streams and rivers around the globe. This study describes the design of a laboratory-scale flow-through incubation system as a tool for the rapid estimation of sediment respiration. The measurements were compared with those obtained using an in situ closed chamber respiration method. The influence of sediment size on respiration rates was also investigated.Materials and methodsMeasurements were conducted on a pre-alpine gravel-bed river sediment separated into the following grain size fractions: > 60 mm (14.3%), 60–5 mm (60.2%), 5–2 mm (13.7%), 2–0.063 mm (11.1%) and <0.063 mm (0.6%). Concurrently, in situ and laboratory measurements were carried out on a naturally heterogeneous sediment. In situ respiration was determined in closed chambers as O2 consumption over time, while in the laboratory, respiration was determined using flow-through respiration chambers. Oxygen concentrations were measured using a fibre-optic oxygen meter positioned at the inflow and outflow from the chamber.Results and discussionThe mean respiration rates within naturally mixed riverbed sediments were 1.27 ± 0.3 mg O2 dm?3 h?1 (n = 4) and 0.77 ± 0.1 mg O2 dm?3 h?1 (n = 3) for the flow-through chamber system and closed chamber system, respectively. Respiration rates were statistically significantly higher in the flow-through chamber system (t test, p < 0.05), indicating that closed chamber measurements underestimated the oxygen consumption within riverbed sediments. Sediment grain size was found to significantly affect respiration rates in both systems (ANOVA, p < 0.001) with the fine sediment fraction (particle size <0.063 mm) having the highest respiration rate (rflow-through = 51 ± 23 mg O2 dm?3 h?1). The smallest fractions (2–0.063 and <0.063 mm), which represent approximately 12% of total sediment volume, contributed 60% of total respiration.ConclusionsThe study demonstrated that flow-through respiration chambers more accurately estimate the respiration rate within riverbed sediments than in situ closed chambers, since the former experiment imitates the natural conditions where continuous interstitial flow occurs in the sediments. We also demonstrated that fine sediments (<5 mm) substantially contribute to heterotrophic respiration in the studied gravel-bed river. 相似文献
8.
Since the development of effective N 2O mitigation options is a key challenge for future agricultural practice, we studied the interactive effect of tillage systems on fertilizer-derived N 2O emissions and the abundance of microbial communities involved in N 2O production and reduction. Soil samples from 0–10 cm and 10–20 cm depth of reduced tillage and ploughed plots were incubated with dairy slurry (SL) and manure compost (MC) in comparison with calcium ammonium nitrate (CAN) and an unfertilized control (ZERO) for 42 days. N 2O and CO 2 fluxes, ammonium, nitrate, dissolved organic C, and functional gene abundances (16S rRNA gene, nirK, nirS, nosZ, bacterial and archaeal amoA) were regularly monitored. Averaged across all soil samples, N 2O emissions decreased in the order CAN and SL (CAN?=?748.8?±?206.3, SL?=?489.4?±?107.2 μg kg ?1) followed by MC (284.2?±?67.3 μg kg ?1) and ZERO (29.1?±?5.9 μg kg ?1). Highest cumulative N 2O emissions were found in 10–20 cm of the reduced tilled soil in CAN and SL. N 2O fluxes were assigned to ammonium as source in CAN and SL and correlated positively to bacterial amoA abundances. Additionally, nosZ abundances correlated negatively to N 2O fluxes in the organic fertilizer treatments. Soils showed a gradient in soil organic C, 16S rRNA, nirK, and nosZ with greater amounts in the 0–10 than 10–20 cm layer. Abundances of bacterial and archaeal amoA were higher in reduced tilled soil compared to ploughed soils. The study highlights that tillage system induced biophysicochemical stratification impacts net N 2O emissions within the soil profile according to N and C species added during fertilization. 相似文献
9.
Lentic wetlands are usually regarded as the most important natural freshwater sources of methane (CH 4) and nitrous oxide (N 2O) to the atmosphere, and very few studies have quantified the importance of lowland streams in trace gas emissions. In this study, we estimated fluxes of CH 4 and N 2O in three macrophyte-rich, lowland agricultural streams in New Zealand, to place their trace gas emissions in context with other sources and investigate the value of minimising their emissions from agricultural land. All three streams were net sources of both gases, with emission of CH 4 ranging from <1 to 500 μmol m ?2 h ?1 and of N 2O ranging from <1 to 100 μmol m ?2 h ?1 during mid-summer. For CH 4, both turbulent diffusion across the surface and ebullition of sediment gas bubbles were important transport processes, with ebullition accounting for 20–60% of the emissions at different sites. The emissions were similar on a per area basis to other major global sources of CH 4 and N 2O. Although small on a catchment scale compared to emissions from intensively grazed pastures, they were significant relative to low-intensity pastures and other agricultural land uses. Because hydraulic variables (viz. depth, velocity and slope) strongly influence turbulent diffusion, complete denitrification can best proceed to N 2 as the dominant end-product (rather than N 2O) in riparian wetlands, rather than in open stream channels where N 2O fluxes are sometimes very large. 相似文献
10.
PurposeOrganic matter amendment is usually used to improve soil physicochemical properties and to sequester carbon for counteracting climate change. There is no doubt that such amendment will change microbial activity and soil nitrogen transformation processes. However, the effects of straw and biochar amendment on anammox and denitrification activity and on community structure in paddy soil are unclear.Materials and methodsWe conducted a 30-day pot experiment using rice straw and rice straw biochar to deepen our understanding about the activity, microbial abundance, and community structure associated with soil nitrogen cycling during rice growth.Results and discussionRegarding activity, anammox contributed 3.1–8.1% of N2 production and denitrification contributed 91.9–96.9% of N2 production; straw amendment resulted in the highest denitrification rate (38.9 nmol N g?1 h?1), while biochar amendment resulted in the highest anammox rate (1.60 nmol N g?1 h?1). Both straw and biochar amendments significantly increased the hzsB and nosZ gene abundance (p < 0.05). Straw amendment showed the highest nosZ gene abundance, while biochar amendment showed the highest hzsB gene abundance. Phylogenetic analysis of the anammox bacteria 16S rRNA genes indicated that Candidatus Brocadia and Kuenenia were the dominant genera detected in all treatments.ConclusionsStraw and biochar amendments have different influences on anaerobic ammonia oxidation and denitrification within paddy soil. Our results suggested that the changes in denitrification and anammox rates in the biochar and straw treatments were mainly linked to functional gene abundance rather than microbial community structure and that denitrification played the more major role in N2 production in paddy soil. 相似文献
11.
Purpose Carbon (C) dynamics in grassland ecosystem contributes to regional and global fluxes in carbon dioxide (CO 2) concentrations. Grazing is one of the main structuring factors in grassland, but the impact of grazing on the C budget is still under debate. In this study, in situ net ecosystem CO 2 exchange (NEE) observations by the eddy covariance technique were integrated with a modified process-oriented biogeochemistry model (denitrification–decomposition) to investigate the impacts of grazing on the long-term C budget of semiarid grasslands. Materials and methods NEE measurements were conducted in two adjacent grassland sites, non-grazing (NG) and moderate grazing (MG), during 2006–2007. We then used daily weather data for 1978–2007 in conjunction with soil properties and grazing scenarios as model inputs to simulate grassland productivity and C dynamics. The observed and simulated CO 2 fluxes under moderate grazing intensity were compared with those without grazing. Results and discussion NEE data from 2-year observations showed that moderate grazing significantly decreased grassland ecosystem CO 2 release and shifted the ecosystem from a negative CO 2 balance (releasing 34.00 g C?m ?2) at the NG site to a positive CO 2 balance (absorbing ?43.02 g C?m ?2) at the MG site. Supporting our experimental findings, the 30-year simulation also showed that moderate grazing significantly enhances the CO 2 uptake potential of the targeted grassland, shifting the ecosystem from a negative CO 2 balance (57.08?±?16.45 g C?m ?2?year ?1) without grazing to a positive CO 2 balance (?28.58?±?14.60 g C?m ?2?year ?1) under moderate grazing. The positive effects of grazing on CO 2 balance could primarily be attributed to an increase in productivity combined with a significant decrease of soil heterotrophic respiration and total ecosystem respiration. Conclusions We conclude that moderate grazing prevails over no-management practices in maintaining CO 2 balance in semiarid grasslands, moderating and mitigating the negative effects of global climate change on the CO 2 balance in grassland ecosystems. 相似文献
12.
Abstract To determine the means and variations in CH 4 uptake and N 2O emission in the dominant soil and vegetation types to enable estimation of annual gases fluxes in the forest land of Japan, we measured monthly fluxes of both gases using a closed-chamber technique at 26 sites throughout Japan over 2 years. No clear seasonal changes in CH 4 uptake rates were observed at most sites. N 2O emission was mostly low throughout the year, but was higher in summer at most sites. The annual mean rates of CH 4 uptake and N 2O emission (all sites combined) were 66 (2.9–175) µg CH 4-C m ?2 h ?1 and 1.88 (0.17–12.5) µg N 2O-N m ?2 h ?1, respectively. Annual changes in these fluxes over the 2 years were small. Significant differences in CH 4 uptake were found among soil types ( P < 0.05). The mean CH 4 uptake rates (µg CH 4-C m ?2 h ?1) were as follows: Black soil (95 ± 39, mean ± standard deviation [SD]) > Brown forest soil (60 ± 27) ≥ other soils (20 ± 24). N 2O emission rates differed significantly among vegetation types ( P < 0.05). The mean N 2O emission rates (µg N 2O-N m ?2 h ?1) were as follows: Japanese cedar (4.0 ± 2.3) ≥ Japanese cypress (2.6 ± 3.4) > hardwoods (0.8 ± 2.2) = other conifers (0.7 ± 1.4). The CH 4 uptake rates in Japanese temperate forests were relatively higher than those in Europe and the USA (11–43 µg CH 4-C m ?2 h ?1), and the N 2O emission rates in Japan were lower than those reported for temperate forests (0.23–252 µg N 2O-N m ?2 h ?1). Using land area data of vegetation cover and soil distribution, the amount of annual CH 4 uptake and N 2O emission in the Japanese forest land was estimated to be 124 Gg CH 4-C year ?1 with 39% uncertainty and 3.3 Gg N 2O-N year ?1 with 76% uncertainty, respectively. 相似文献
13.
To understand spatial and temporal variations of nitrous oxide (N 2O) fluxes, we chose to measure N 2O emissions from three plant stands ( Kobresia tibetica, Carex muliensis, and Eleocharis valleculosa stands) in an open fen on the northeastern Qinghai?CTibetan plateau during the growing seasons from 2005 to 2007. The overall mean N 2O emission rate was about 0.018?±?0.056?mg?N?m ?2?h ?1 during the growing seasons from 2005 to 2007, with highly spatiotemporal variations. The hummock ( K. tibetica stand) emitted N 2O at the highest rate about 0.025?±?0.051?mg?N?m ?2?h ?1, followed by the hollow stands: the E. valleculosa stand about 0.012?±?0.046?mg?N?m ?2?h ?1 and the C. muliensis stand about 0.017?±?0.068?mg?N?m ?2?h ?1. Within each stand, we also noted significant variations of N 2O emission. We also observed the significant seasonal and inter-annual variation of N 2O fluxes during the study period. The highest N 2O emission rate was all recorded in July or August in each year from 2005 to 2007. Compared with the mean value of 2005, we found the drought of 2006 significantly increased N 2O emissions by 104 times in the E. valleculosa stand, 45 times in K. tibetica stand, and 18 times in the C. muliensis stand. Though there was no significant relation between standing water depths and N 2O emissions, we still considered it related to the spatiotemporal dynamics of soil water regime under climate change. 相似文献
14.
Nitrous oxide is produced in soils by biological denitrification and nitrification. To improve the fundamental understanding of the processes leading to N 2O fluxes from soils, the production of N 2O from denitrification and nitrification in spruce forest, beech forest, riparian grassland, coastal grassland and an agricultural field were studied. Samples were taken at a high and a low position along a topographic gradient in each site in the spring and autumn when the largest N 2O fluxes were expected. They were incubated after being amended with N, and C 2H 2 was used as biological inhibitor to distinguish nitrification and denitrification. The N 2O production in the low landscape position varied between 32 and 121 ng N cm ?3 h ?1 in the riparian grassland. 9 and 26 ng N cm ?3 h ?1 in the coastal grassland, and 135 and 195 ng N cm ?3 h ?1 in the agricultural field which was 10–100 times more than in the high positions where rates ranged between 3 and 5 ng N cm ?3 h ?1, 0.3 and 0.4 ng N cm ?3 h ?1, and 7 and 10 ng N cm ?3 h ?1, respectively. These differences almost certainly arose because the soil in the low positions was wetter and contained more organic matter. In the two forests N 2O production was less than 1 ng N cm ?3 h ?1, strongly inhibited by O 2, and not influenced by landscape position. Nitrification contributed to more than 60% of total N 2O production in the riparian grassland. In the agricultural field nitrification produced 13–74% of the total N 2O in the low position, and 10–88% in the high position. Denitrification was the dominant source of N 2O in the coastal grassland except at the low position in the autumn where nitrification produced 60% of the total N 2O. In the two forests where the soil had small nitrification potentials denitrification was the only source of N 2O. In the other sites nitrification and denitrification potentials were large and of identical magnitude. The results emphasize the need to separate nitrification and denitrification at the process level and to recognize topography at the field scale when modelling N 2O effluxes from soil. 相似文献
15.
Abstract To develop an advanced method for estimating nitrous oxide (N 2O) emission from an agricultural watershed, we used a closed-chamber technique to measure seasonal N 2O and nitric oxide (NO) fluxes in cornfields, grassland, pastures and forests at the Shizunai Experimental Livestock Farm (467 ha) in southern Hokkaido, Japan. From 2000 to 2004, N 2O and NO fluxes ranged from –137 to 8,920 µg N m ?2 h ?1 and from –12.1 to 185 µg N m ?2 h ?1, respectively. Most N 2O/NO ratios calculated on the basis of these N 2O and NO fluxes ranged between 1 and 100, and the log-normal N 2O/NO ratio was positively correlated with the log-normal N 2O fluxes ( r 2 = 0.346, P < 0.01). These high N 2O fluxes, therefore, resulted from increased denitrification activity. Annual N 2O emission rates ranged from –1.0 to 81 kg N ha ?1 year ?1 (average = 6.6 kg N ha ?1). As these emission values varied greatly and included extremely high values, we divided them into two groups: normal values (i.e. values lower than the overall average) and high values (i.e. values higher than average). The normal data were significantly positively correlated with N input ( r 2 = 0.61, P < 0.01) and the “higher” data from ungrazed fields were significantly positively correlated with N surplus ( r 2 = 0.96, P < 0.05). The calculated probability that a high N 2O flux would occur was weakly and positively correlated with precipitation from May to August. This probability can be used to represent annual variation in N 2O emission rates and to reduce the uncertainty in N 2O estimation. 相似文献
16.
Wood ash has been used to alleviate nutrient deficiencies and acidification in boreal forest soils. However, ash and nitrogen (N) fertilization may affect microbial processes producing or consuming greenhouse gases: methane (CH 4), nitrous oxide (N 2O) and carbon dioxide (CO 2). Ash and N fertilization can stimulate nitrification and denitrification and, therefore, increase N 2O emission and suppress CH 4 uptake rate. Ash may also stimulate microbial respiration thereby enhancing CO 2 emission. The fluxes of CH 4, N 2O and CO 2 were measured in a boreal spruce forest soil treated with wood ash and/or N (ammonium nitrate) during three growing seasons. In addition to in situ measurements, CH 4 oxidation potential, CO 2 production, net nitrification and N 2O production were studied in laboratory incubations. The mean in situ N 2O emissions and in situ CO 2 production from the untreated, N, ash and ash + N treatments were not significantly different, ranging from 11 to 17 μg N 2O m ?2 h ?1 and from 533 to 611 mg CO 2 m ?2 h ?1. However, ash increased the CH 4 oxidation in a forest soil profile which could be seen both in the laboratory experiments and in the CH 4 uptake rates in situ. The mean in situ CH 4 uptake rate in the untreated, N, ash and ash + N plots were 153 ± 5, 123 ± 8, 188 ± 10 and 178 ± 18 μg m ?2 h ?1, respectively. 相似文献
17.
PurposeThe purposes of this study were to analyse the spatiotemporal variations in greenhouse gas diffusive fluxes at the sediment–water interface of sewage-draining rivers and natural rivers, and investigate the factors responsible for the changes in greenhouse gas diffusive fluxes. Materials and methodsGreenhouse gas diffusive fluxes at the sediment–water interface of rivers in Tianjin city (Haihe watershed) were investigated during July and October 2014, and January and April 2015 by laboratory incubation experiments. The influence of environmental variables on greenhouse gas diffusive fluxes was evaluated by Spearman’s correlation analysis and a multiple stepwise regression analysis. Results and discussionSewage-draining rivers were more seriously polluted by human sewage discharge than natural rivers. The greenhouse gas diffusive fluxes at the sediment–water interface exhibited obvious spatiotemporal variations. The mean absolute value of the CO2 diffusive fluxes was seasonally variable with spring>winter>fall>summer, while the mean absolute values of the CH4 and N2O diffusive fluxes were both higher in summer and winter, and lower in fall and spring. The annual mean values of the CO2, CH4 and N2O diffusive fluxes at the sewage-draining river sediment–water interface were ??123.26?±?233.78 μmol m?2 h?1, 1.88?±?6.89 μmol m?2 h?1 and 1505.03?±?2388.46 nmol m?2 h?1, respectively, which were 1.22, 4.37 and 134.50 times those at the natural river sediment–water interface, respectively. The spatial variation of the N2O diffusive fluxes in the sewage-draining rivers and the natural rivers was the most significant. As a general rule, the more serious the river pollution was, the greater the diffusive fluxes of the greenhouse gases were. On average for the whole year, the river sediment was the sink of CO2 and the source of CH4 and N2O. There were positive correlations among the CO2, CH4 and N2O diffusive fluxes. The main influencing factor for CO2 and N2O diffusive fluxes was the water temperature of the overlying water; however, the key factors for CH4 diffusive fluxes were the Eh of the sediment and the NH4+-N of the overlying water. ConclusionsRiver sediment can be either a sink or a source of greenhouse gases, which varies in different levels of pollution and different seasons. Human sewage discharge has greatly affected the carbon and nitrogen cycling of urban rivers. 相似文献
18.
Anaerobic ammonium oxidation (anammox process) widely occurs in paddy soil and may substantially contribute to permanent N removal; however, little is known about the factors controlling this process. Here, effects of temperature, pH, organic C, and substrates on potential rate of anammox and the relative contribution of anammox to total N 2 production in a paddy soil were investigated via slurry incubation combined with 15N tracer technique. Anammox occurred over a temperature range from 5 to 35 °C with an optimum rate at 25 °C (1.7 nmol N g ?1 h ?1) and a pH range from 4.8 to 10.1 with an optimum rate at pH 7.3 (1.7 nmol N g ?1 h ?1). The presence of glucose and acetate (5–100 mg C L ?1) significantly inhibited anammox activities and the ratio of anammox to total N 2 production. The response of potential rates of anammox to ammonium concentrations fitted well with Michaelis-Menten relationship showing a maximum rate ( Vmax) of 4.4 nmol N g ?1 h ?1 and an affinity constant ( Km) of 6.3 mg NH 4+-N L ?1. Whereas, nitrate addition (5–15 mg 15NO 3?-N L ?1) significantly inhibited anammox activities and the ratio of anammox to total N 2 production. Our results provide useful information on factors controlling anammox process and its contribution to N loss in the paddy soil. 相似文献
19.
This study aimed to understand the seasonal and spatial variations of N 2O emissions from newly created littoral marshes in the drawdown area of the Three Gorges Reservoir (TGR), China. We measured N 2O emissions at 10-day intervals during the growing season (early July to late September) in 2008. N 2O emissions were measured with static chambers in four typical vegetation stands. The results showed great spatial variations of N 2O emissions among the four stands. The greatest N 2O emissions (0.052?±?0.063 mg N 2O m ?2?h ?1) were from Scirpus triqueter stand, while the lowest N 2O emissions (0.020?±?0.020 mg N 2O m ?2?h ?1) were from Typha angustifolia stand. To such spatial variations in N 2O emissions, standing water depths and soil water content may be important explaining factors. Besides spatial variations, we also found significant temporal variations of N 2O emissions in this area. The temporal variation of N 2O emissions in the growing season was not found significantly related to any measured factor in the study. However, based on principal component analysis, we consider it partly caused by thermal conditions and the marked temporal variation of the standing water depth in the growing season, which to some degree influenced the process of denitrification and N 2O emissions. These results about TGR enable us to make a more reasonable estimate of N 2O emissions from large dam reservoirs, particularly those with a large drawdown area in the growing season in an agricultural landscape. 相似文献
20.
To determine nitrogen (N) fate and environmental impact of applying anaerobic digestion slurry (ADS) to rice paddy ( Oryza sativa L.), a field experiment was established using three treatments based on contrasting N application rate. The ADS (with ammonium-N accounting for >80 % of total N) treatment at a conventional application rate of 270 kg N?ha ?1 was compared to a negative control (no N fertilizer) and a positive control of urea applied at 270 kg N?ha ?1. The N budget showed the following distribution of applied N from ADS and urea: 41.3?±?5.1 % for ADS and 36.6?±?4.4 % for urea recovered by the rice plant (including straw, grain, and root), 16.4?±?3.7 % for ADS and 7.4?±?1.8 % for urea lost via ammonia volatilization, 0.26?±?0.15 % for ADS and 0.15?±?0.12 % for urea lost by direct N 2O emission, 1.9?±?0.5 % for ADS and 2.3?±?0.8 % for urea leached downward, 0.70?±?0.15 % for ADS and 0.67?±?0.12 % for urea discharged with floodwater drainage, and 39.4?±?8.4 % for ADS and 53.0?±?9.1 % for urea retained by soil or lost by N 2 emission. Compared to urea application, ADS application impacts the environment mainly through gaseous N losses rather than water N losses. ADS application had a positive impact on rice grain yield and reduced chemical fertilizer use. Considering the wide distribution of paddy fields and the ever-increasing quantities of ADS, ADS may serve as a valuable N source for rice cultivation, although mitigating ammonia and N 2O losses should be further investigated. 相似文献
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