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1.
During a field experiment applying broiler manure for fertilization of agricultural land, we detected viable Clostridioides (also known as Clostridium) difficile in broiler faeces, manure, dust and fertilized soil. A large diversity of toxigenic C. difficile isolates was recovered, including PCR ribotypes common from human disease. Genomic relatedness of C. difficile isolates from dust and from soil, recovered more than 2 years after fertilization, traced their origins to the specific chicken farm that had delivered the manure. We present evidence of long-term contamination of agricultural soil with manure-derived C. difficile and demonstrate the potential for airborne dispersal of C. difficile through dust emissions during manure application. Clostridioides genome sequences virtually identical to those from manure had been recovered from chicken meat and from human infections in previous studies, suggesting broiler-associated C. difficile are capable of zoonotic transmission. 相似文献
2.
The objective of this study was to estimate the possible travel distance of airborne bacteria emitted from a naturally ventilated
broiler house by using staphylococci as indicator organisms. Air samples were taken during the second half of three fattening
periods with Impinger (AGI-30) in the barn and simultaneously upwind and downwind from the building. Staphylococci concentrations
varied between 1 × 10 6 and 1 × 10 7 cfu m −3 in the barn. No Staphylococci were detected in air samples at the upwind side. A strong exponential decrease of these bacteria
was observed at three sampling heights (1.5, 4.0 and 9.5 m) in the main wind direction downwind of the barn. Staphylococci
concentrations up to 5.9 × 10 3 cfu m −3 were detected at the farthest sampling point (333 m) downwind. Identification to the species level by means of a 16S–23S
ITS PCR confirmed that Staphylococcus spp. from downwind samples originated from the barn. Staphylococci served as an useful indicator to demonstrate the travel
distance of bacterial emissions originating from a naturally ventilated broiler house. These findings indicate that airborne
transmission of viable bacteria from this type of housing system to adjacent residential dwellings or animal houses several
hundred metres away is possible. 相似文献
3.
The need for sustainability in food supply has led to progressive increase in soil nutrient enrichment. Fertilizer application effects both biological and abiotic processes in the soil, of which the bacterial community that support viral multiplication are equally influenced. Nevertheless, little is known on the effect of soil fertilization on the Soil viral community composition and dynamics. In this study, we evaluated the influence of soil fertilization on the maize rhizosphere viral community growing in Luvisolic soil. The highest abundance of bacteriophages were detected in soil treated with 8 tons/ha compost manure (Cp8), 60 kg/ha inorganic fertilizer (N1), 4 tons/ha compost manure (Cp4) and the unfertilized control (Cn0). Our result showed higher relative abundance of Myoviridae, Podoviridae and Siphoviridae in 8 tons/ha organic manure (Cp8) fertilized compared to others. While Inoviridae and Microviridae were the most relative abundant phage families in 4 tons/ha organic manure (Cp4) fertilized soil. This demonstrate that soil fertilization with organic manure increases the abundance and diversity of viruses in the soil due to its soil conditioning effects.
相似文献
4.
Urban land-use change has the potential to affect local to global biogeochemical carbon (C) and nitrogen (N) cycles and associated greenhouse gas (GHG) fluxes. We conducted a meta-analysis to (1) assess the effects of urbanization-induced land-use conversion on soil nitrous oxide (N 2O) and methane (CH 4) fluxes, (2) quantify direct N 2O emission factors (EF d) of fertilized urban soils used, for example, as lawns or forests, and (3) identify the key drivers leading to flux changes associated with urbanization. On average, urbanization increases soil N 2O emissions by 153%, to 3.0 kg N ha −1 year −1, while rates of soil CH 4 uptake are reduced by 50%, to 2.0 kg C ha −1 year −1. The global mean annual N 2O EF d of fertilized lawns and urban forests is 1.4%, suggesting that urban soils can be regional hotspots of N 2O emissions. On a global basis, conversion of land to urban greenspaces has increased soil N 2O emission by 0.46 Tg N 2O-N year −1 and decreased soil CH 4 uptake by 0.58 Tg CH 4-C year −1. Urbanization driven changes in soil N 2O emission and CH 4 uptake are associated with changes in soil properties (bulk density, pH, total N content, and C/N ratio), increased temperature, and management practices, especially fertilizer use. Overall, our meta-analysis shows that urbanization increases soil N 2O emissions and reduces the role of soils as a sink for atmospheric CH 4. These effects can be mitigated by avoiding soil compaction, reducing fertilization of lawns, and by restoring native ecosystems in urban landscapes. 相似文献
5.
Intensive dairy farming systems are a large source of emission of the greenhouse gas nitrous oxide (N 2O), because of high nitrogen (N) application rates to grasslands and silage maize fields. The objective of this study was to compare measured N 2O emissions from two different soils to default N 2O emission factors, and to look at alternative emission factors based on (i) the N uptake in the crop and (ii) the N surplus of the system, i.e., N applied minus N uptake by the crop. Twelve N fertilization regimes were implemented on a sandy soil (typic endoaquoll) and a clay soil (typic endoaquept) in the Netherlands, and N 2O emissions were measured throughout the growing season. Highest cumulative fluxes of 1.92 and 6.81 kg N 2O-N ha –1 for the sandy soil and clay soil were measured at the highest slurry application rate of 250 kg N ha –1. Background emissions from unfertilized soils were 0.14 and 1.52 kg N 2O-N ha –1 for the sandy soil and the clay soil, respectively. Emission factors for the sandy soil averaged 0.08, 0.51 and 0.26% of the N applied via fertilizer, slurry, and combinations of both. For the clay soil, these numbers were 1.18, 1.21 and 1.69%, respectively. Surplus N was linearly related to N 2O emission for both the sandy soil (R 2=0.60) and the clay soil (R 2=0.40), indicating a possible alternative emission factor. We concluded that, in our study, N 2O emission was not linearly related to N application rates, and varied with type and application rate of fertilizer. Finally, the relatively high emission from the clay soil indicates that background emissions might have to be taken into account in N 2O budgets. 相似文献
6.
A field experiment was carried out at a pilot plot that was cropped with oilseed rape, and then left partly fallow and partly
cropped with a green manure (mustard) during the autumn after harvest of the oilseed rape. The rape residues were incorporated
in the soil. Methods used to quantify the N fluxes from harvest until sowing of the next crop were (1) 15N balance method, (2) total mineral N analysis and (3) NO emission measurements. Losses of spring applied fertilizer N were
negligible in cropped plots and minimal in fallow plots during the following autumn-winter period. Most of the plant-N residues
was retained by the organic N pool of the upper 30-cm soil layer. The green manure contributed slightly to soil available
N at sowing of the next crop. However, the incorporation of plant material resulted in a nitrate flux that was at risk of
leaching on the fallow plots, and on the green manure plots after incorporation of the green manure. This nitrate was largely
derived from soil organic N, not from unused fertilizer applied in spring or from immobilized fertilizer.
The NO emissions from the green manure plots were significantly higher than emissions from the fallow plots. The plants had
a stimulating effect on the NO emission. A relationship between the NO emission and the soil nitrate concentration could not
be established. No emissions were measured after green manure incorporation due to the low temperatures at the pilot plot.
However, a greenhouse experiment showed an increased emission after incorporation. The NO emissions seemed to be related with
the soil ammonium concentration. 相似文献
7.
Nitrous oxide fluxes and soil nitrogen transformations were measured in experimentally-treated high elevation Douglas-fir
forests in northwestern New Mexico, USA. On an annual basis, forests that were fertilized with 200 kg N/ha emitted an average
of 0.66 kg/ha of N 2O-N, with highest fluxes occurring in July and August when soils were both warm and wet. Control, irrigated, and woodchip
treated plots were not different from each other, and annual average fluxes ranged from 0.03 to 0.23 kg/ha. Annual net nitrogen
mineralization and nitrate production were estimated in soil and forest floor using in situ incubations; fertilized soil mineralized 277 kg ha −1 y −1 in contrast to 18 kg ha −1 y −1 in control plots. Relative recovery of 15NH 4-N applied to soil in laboratory incubations was principally in the form of NO 3-N in the fertilized soils, while recovery was mostly in microbial biomass-N in the other treatments. Fertilization apparently
added nitrogen that exceeded the heterotrophic microbial demand, resulting in higher rates of nitrate production and higher
nitrous oxide fluxes. Despite the elevated nitrous oxide emission resulting from fertilization, we estimate that global inputs
of nitrogen into forests are not currently contributing significantly to the increasing concentrations of nitrous oxide in
the atmosphere. 相似文献
8.
Tropical peatlands are vital ecosystems that play an important role in global carbon storage and cycles. Current estimates of greenhouse gases from these peatlands are uncertain as emissions vary with environmental conditions. This study provides the first comprehensive analysis of managed and natural tropical peatland GHG fluxes: heterotrophic (i.e. soil respiration without roots), total CO 2 respiration rates, CH 4 and N 2O fluxes. The study documents studies that measure GHG fluxes from the soil ( n = 372) from various land uses, groundwater levels and environmental conditions. We found that total soil respiration was larger in managed peat ecosystems (median = 52.3 Mg CO 2 ha ?1 year ?1) than in natural forest (median = 35.9 Mg CO 2 ha ?1 year ?1). Groundwater level had a stronger effect on soil CO 2 emission than land use. Every 100 mm drop of groundwater level caused an increase of 5.1 and 3.7 Mg CO 2 ha ?1 year ?1 for plantation and cropping land use, respectively. Where groundwater is deep (≥0.5 m), heterotrophic respiration constituted 84% of the total emissions. N 2O emissions were significantly larger at deeper groundwater levels, where every drop in 100 mm of groundwater level resulted in an exponential emission increase (exp(0.7) kg N ha ?1 year ?1). Deeper groundwater levels induced high N 2O emissions, which constitute about 15% of total GHG emissions. CH 4 emissions were large where groundwater is shallow; however, they were substantially smaller than other GHG emissions. When compared to temperate and boreal peatland soils, tropical peatlands had, on average, double the CO 2 emissions. Surprisingly, the CO 2 emission rates in tropical peatlands were in the same magnitude as tropical mineral soils. This comprehensive analysis provides a great understanding of the GHG dynamics within tropical peat soils that can be used as a guide for policymakers to create suitable programmes to manage the sustainability of peatlands effectively. 相似文献
9.
Willow coppice, energy maize and Miscanthus were evaluated regarding their soil‐derived trace gas emission potential involving a nonfertilized and a crop‐adapted slow‐release nitrogen (N) fertilizer scheme. The N application rate was 80 kg N ha ?1 yr ?1 for the perennial crops and 240 kg N ha ?1 yr ?1 for the annual maize. A replicated field experiment was conducted with 1‐year measurements of soil fluxes of CH 4, CO 2 and N 2O in weekly intervals using static chambers. The measurements revealed a clear seasonal trend in soil CO 2 emissions, with highest emissions being found for the N‐fertilized Miscanthus plots (annual mean: 50 mg C m ?² h ?1). Significant differences between the cropping systems were found in soil N 2O emissions due to their dependency on amount and timing of N fertilization. N‐fertilized maize plots had highest N 2O emissions by far, which accumulated to 3.6 kg N 2O ha ?1 yr ?1. The contribution of CH 4 fluxes to the total soil greenhouse gas subsumption was very small compared with N 2O and CO 2. CH 4 fluxes were mostly negative indicating that the investigated soils mainly acted as weak sinks for atmospheric CH 4. To identify the system providing the best ratio of yield to soil N 2O emissions, a subsumption relative to biomass yields was calculated. N‐fertilized maize caused the highest soil N 2O emissions relative to dry matter yields. Moreover, unfertilized maize had higher relative soil N 2O emissions than unfertilized Miscanthus and willow. These results favour perennial crops for bioenergy production, as they are able to provide high yields with low N 2O emissions in the field. 相似文献
10.
Direct field emissions of nitrous oxide (N 2O) may determine whether biodiesel from oilseed rape ( Brassica napus L.) fulfills the EU requirement of at least 50% reduction of greenhouse gas emissions as compared to fossil diesel. However, only few studies have documented fertilizer N emission factors (EF) and mitigation options for N 2O emissions from oilseed rape cropping systems. We conducted a field experiment with three N levels (0, 171, and 217 kg/ha), where the N fertilizer was applied as ammonium sulfate nitrate with or without the nitrification inhibitor 3,4‐dimethylpyrazole phosphate (DMPP). N 2O fluxes were measured using static chambers technique and soil samples were analyzed for water and mineral N content during a monitoring period of 368 days. The DMPP treatments showed a significantly increased level of ammonium () for up to 18 weeks after spring fertilization as compared to the treatments without DMPP. However, this difference did not result in a corresponding decrease in soil content, and no differences in cumulative N 2O emissions were found between any fertilized treatments with or without DMPP (mean, 1.26 kg N 2O‐N ha ?1 year ?1). More field experiments are needed to clarify whether DMPP‐coated mineral fertilizers could mitigate N 2O emissions under different weather conditions, for example, under conditions where fertilization events concurred with rainfall events increasing water‐filled pore space to the assumed 60% threshold for denitrification. Emission factors for mineral N fertilizer were 0.28%–0.36% with a mean of 0.32% across the fertilized treatments. These data concur with recent European studies suggesting that the EF for mineral N fertilizers in oilseed rape cropping systems may typically be lower than the default IPCC value of 1%. Further studies are needed to consolidate an EF for oilseed rape under temperate conditions, which will be determining for the sustainability of Northern European oilseed rape cultivation for biodiesel. 相似文献
11.
The soil emission rates (fluxes) of nitrous oxide (N 2O) and nitrogen oxides (NO + NO 2 = NO
x
) through a seasonal snowpack were determined by a flux gradient method from near-continuous 2-year measurements using an
automated system for sampling interstitial air at various heights within the snowpack from a subalpine site at Niwot Ridge,
Colorado. The winter seasonal-averaged N 2O fluxes of 0.047–0.069 nmol m −2 s −1 were ~15 times higher than observed NO
x
fluxes of 0.0030–0.0067 nmol m −2 s −1. During spring N 2O emissions first peaked and then dropped sharply as the soil water content increased from the release of snowpack meltwater,
while other gases, including NO
x
and CO 2 did not show this behavior. To compare and contrast the winter fluxes with snow-free conditions, N 2O fluxes were also measured at the same site in the summers of 2006 and 2007 using a closed soil chamber method. Summer N 2O fluxes followed a decreasing trend during the dry-out period after snowmelt, interrupted by higher values related to precipitation
events. These peaks were up to 2–3 times higher than the background summer levels. The integrated N 2O-N loss over the summer period was calculated to be 1.1–2.4 kg N ha −1, compared to ~0.24–0.34 kg N ha −1 for the winter season. These wintertime N 2O fluxes from subniveal soil are generally higher than the few previously published data. These results are of the same order
of magnitude as data from more productive ecosystems such as fertilized grasslands and high-N-cycling forests, most likely
because of a combination of the relatively well-developed soils and the fact that subnivean biogeochemical processes are promoted
by the deep, insulating snowpack. Hence, microbially mediated oxidized nitrogen emissions occurring during the winter can
be a significant part of the N-cycle in seasonally snow-covered subalpine ecosystems. 相似文献
12.
Monoculture croplands are a major source of global anthropogenic emissions of nitrous oxide (N 2O), a potent greenhouse gas that contributes to ozone depletion. Agroforestry has the potential to reduce N 2O emissions. Presently, there is no systematic comparison of soil N 2O emissions between cropland agroforestry and monoculture systems in Central Europe. We investigated the effects of converting the monoculture cropland system into the alley cropping agroforestry system on soil N 2O fluxes at three sites (each site has paired agroforestry and monoculture) in Germany, where agroforestry combined crop rows and poplar short-rotation coppice (SRC). We measured soil N 2O fluxes monthly over 2 years (March 2018–January 2020) using static vented chambers. Annual soil N 2O emissions from agroforestry ranged from 0.21 to 2.73 kg N ha −1 year −1, whereas monoculture N 2O emissions ranged from 0.34 to 3.00 kg N ha −1 year −1. During the rotation of corn crop, with high fertilization rates, agroforestry reduced soil N 2O emissions by 9% to 56% compared to monocultures. This was mainly caused by low soil N 2O emissions from the unfertilized agroforestry tree rows. Soil N 2O fluxes were predominantly controlled by soil mineral N in both agroforestry and monoculture systems. Our findings suggest that optimized fertilizer input will further enhance the potential of agroforestry for mitigating N 2O emissions. 相似文献
13.
Livestock manures are broadly used in agriculture to improve soil quality. However, manure application can increase the availability of organic carbon, thereby facilitating methane (CH 4) production. Cattle and swine manures are expected to have different CH 4 emission characteristics in rice paddy soil due to the inherent differences in composition as a result of contrasting diets and digestive physiology between the two livestock types. To compare the effect of ruminant and non-ruminant animal manure applications on CH 4 emissions and methanogenic archaeal diversity during rice cultivation (June to September, 2009), fresh cattle and swine manures were applied into experimental pots at 0, 20 and 40 Mg fresh weight (FW) ha −1 in a greenhouse. Applications of manures significantly enhanced total CH 4 emissions as compared to chemical fertilization, with cattle manure leading to higher emissions than swine manure. Total organic C contents in cattle (466 g kg −1) and swine (460 g kg −1) manures were of comparable results. Soil organic C (SOC) contents were also similar between the two manure treatments, but dissolved organic C (DOC) was significantly higher in cattle than swine manure. The mcrA gene copy numbers were significantly higher in cattle than swine manure. Diverse groups of methanogens which belong to Methanomicrobiaceae were detected only in cattle-manured but not in swine-manured soil. Methanogens were transferred from cattle manure to rice paddy soils through fresh excrement. In conclusion, cattle manure application can significantly increase CH 4 emissions in rice paddy soil during cultivation, and its pretreatment to suppress methanogenic activity without decreasing rice productivity should be considered. 相似文献
14.
【背景】施肥是目前提高作物产量的较优策略,不同的施肥措施在不同程度上影响土壤肥力和微生物群落结构。【目的】探究岩溶水稻土理化性质变化与细菌群落变化的对应关系,进而反映不同施肥措施对土壤可培养细菌群落的影响。最后选出最优施肥方案,为后续的合理施肥工作提供依据。【方法】对岩溶水稻土进行不施肥、常规施肥、常规施肥加绿肥3种施肥处理,通过对土壤理化性质、可培养细菌群落丰度及多样性变化的研究,探究在不同施肥措施下对岩溶水稻土壤细菌群落的影响。【结果】对比不施肥处理,常规施肥处理下土壤pH值和有机碳含量下降,结合大量研究结果证明,无机肥或氮肥的长期过量施加使土壤pH值下降,常规施肥加绿肥有利于有机碳的积累。分离纯化共得到164株菌,分别来自Actinobacteria、Bacteroidetes、Firmicutes和Proteobacteria。属水平上常规施肥配施绿肥较常规施肥组优势菌属Sphingomonas、Lysobacter的相对丰度增加。细菌群落多样性增加,出现Paenibacillus、Streptomyces和Pseudomonas等特有功能菌属。优势菌属Sphingopyxis、Lysobacter、Paenibacillus、Bosea、Streptomyces、Pseudomonas和Bacillus与TN存在显著正相关,在常规施肥加绿肥处理土壤中增加。【结论】常规施肥加绿肥处理下,固氮、溶磷等功能菌丰度增加,增加土壤肥力,保持土壤养分的可利用性,对作物的增产起重要作用。岩溶水稻土常规施肥配施绿肥处理的效果优于不施肥和常规施肥处理。 相似文献
15.
Agricultural drainage is thought to alter greenhouse gas emissions from temperate peatlands, with CH 4 emissions reduced in favor of greater CO 2 losses. Attention has largely focussed on C trace gases, and less is known about the impacts of agricultural conversion on
N 2O or global warming potential. We report greenhouse gas fluxes (CH 4, CO 2, N 2O) from a drained peatland in the Sacramento-San Joaquin River Delta, California, USA currently managed as a rangeland (that
is, pasture). This ecosystem was a net source of CH 4 (25.8 ± 1.4 mg CH 4-C m −2 d −1) and N 2O (6.4 ± 0.4 mg N 2O-N m −2 d −1). Methane fluxes were comparable to those of other managed temperate peatlands, whereas N 2O fluxes were very high; equivalent to fluxes from heavily fertilized agroecosystems and tropical forests. Ecosystem scale
CH 4 fluxes were driven by “hotspots” (drainage ditches) that accounted for less than 5% of the land area but more than 84% of
emissions. Methane fluxes were unresponsive to seasonal fluctuations in climate and showed minimal temporal variability. Nitrous
oxide fluxes were more homogeneously distributed throughout the landscape and responded to fluctuations in environmental variables,
especially soil moisture. Elevated CH 4 and N 2O fluxes contributed to a high overall ecosystem global warming potential (531 g CO 2-C equivalents m −2 y −1), with non-CO 2 trace gas fluxes offsetting the atmospheric “cooling” effects of photoassimilation. These data suggest that managed Delta
peatlands are potentially large regional sources of greenhouse gases, with spatial heterogeneity in soil moisture modulating
the relative importance of each gas for ecosystem global warming potential. 相似文献
16.
The effects of changes in tropical land use on soil emissions of nitrous oxide (N 2O) and nitric oxide (NO) are not well understood. We examined emissions of N 2O and NO and their relationships to land use and forest composition, litterfall, soil nitrogen (N) pools and turnover, soil
moisture, and patterns of carbon (C) cycling in a lower montane, subtropical wet region of Puerto Rico. Fluxes of N 2O and NO were measured monthly for over 1 year in old (more than 60 years old) pastures, early- and mid-successional forests
previously in pasture, and late-successional forests not known to have been in pasture within the tabonuco ( Dacryodes excelsa) forest zone. Additional, though less frequent, measures were also made in an experimentally fertilized tabonuco forest.
N 2O fluxes exceeded NO fluxes at all sites, reflecting the consistently wet environment. The fertilized forest had the highest
N oxide emissions (22.0 kg N · ha −1· y −1). Among the unfertilized sites, the expected pattern of increasing emissions with stand age did not occur in all cases. The
mid-successional forest most dominated by leguminous trees had the highest emissions (9.0 kg N · ha −1· y −1), whereas the mid-successional forest lacking legumes had the lowest emissions (0.09 kg N · ha −1· y −1). N oxide fluxes from late-successional forests were higher than fluxes from pastures. Annual N oxide fluxes correlated positively
to leaf litter N, net nitrification, potential nitrification, soil nitrate, and net N mineralization and negatively to leaf
litter C:N ratio. Soil ammonium was not related to N oxide emissions. Forests with lower fluxes of N oxides had higher rates
of C mineralization than sites with higher N oxide emissions. We conclude that (a) N oxide fluxes were substantial where the
availability of inorganic N exceeded the requirements of competing biota; (b) species composition resulting from historical
land use or varying successional dynamics played an important role in determining N availability; and (c) the established
ecosystem models that predict N oxide loss from positive relationships with soil ammonium may need to be modified.
Received 22 February 2000; accepted 6 September 2000. 相似文献
17.
The present study was conducted to (i) investigate parameters influencing the fluxes of the greenhouse gas methane (CH 4) in Danish riparian wetlands with contrasting vegetation characteristics and (ii) develop models relating CH 4 emissions to soil and/or vegetation parameters integrating the spatial and temporal variability in the fluxes. Fluxes of CH 4 were monitored in 12 wetland plots over a year using static chambers, yielding a dataset with more than 800 measured fluxes of CH 4. Yearly emissions of CH 4 ranged from −0.2 to 38.3 g CH 4-C m −2 year −1, and significant effects of groundwater level, soil temperature (10 cm depth), peat depth, sulfate, nitrate, and soil carbon content were found. Two methods based on easily available environmental parameters to estimate yearly CH 4 emissions from riparian wetlands are presented. The first uses a generalized linear model (GLM) to predict yearly CH 4 emissions based on the humidity preference of vegetation (Ellenberg-F), peat depth and degree of humification of the peat (von Post index). The second method relies solely on plant species composition and uses weighted-average regression and calibration to link the vegetation assemblage to yearly CH 4 emission. Both models gave reliable predictions of the yearly CH 4 fluxes in riparian wetlands (modeling efficiency > 0.35). Our findings support the use of vegetation, possibly in combination with some soil parameters such as peat depth, as indicator of CH 4 emission in wetlands. 相似文献
18.
The use of nitrogen fertilizer on bioenergy crops such as switchgrass results in increased costs, nitrogen leaching and emissions of N 2O, a potent greenhouse gas. Intercropping with nitrogen-fixing alfalfa has been proposed as an environmentally sustainable alternative, but the effects of synthetic fertilizer versus intercropping on soil microbial community functionality remain uncharacterized. We analysed 24 metagenomes from the upper soil layer of agricultural fields from Prosser, WA over two growing seasons and representing three agricultural practices: unfertilized switchgrass (control), fertilized switchgrass and switchgrass intercropped with alfalfa. The synthetic fertilization and intercropping did not result in major shifts of microbial community taxonomic and functional composition compared with the control plots, but a few significant changes were noted. Most notably, mycorrhizal fungi, ammonia-oxidizing archaea and bacteria increased in abundance with intercropping and fertilization. However, only betaproteobacterial ammonia-oxidizing bacteria abundance in fertilized plots significantly correlated to N 2O emission and companion qPCR data. Collectively, a short period of intercropping elicits minor but significant changes in the soil microbial community toward nitrogen preservation and that intercropping may be a viable alternative to synthetic fertilization. 相似文献
19.
In recent years, monitoring of airborne bacteria and fungi concentrations has obtained increasing universal attraction not only for influences on ecological balance but also for evaluating their public health consequences. In this study, we aimed to investigate culturable airborne bacteria and fungi levels in different sites of Abadan, and their association with meteorological parameters and PM2.5 levels. Abadan is one of the most industrialized cities in the southwest of Iran where over the current decade has experienced lots of dust storm episodes. In total, 400 air samples were collected in 6 months (autumn and winter) using a single-stage viable Andersen cascade impactor for sampling airborne bacteria and fungi and portable DustTrak Aerosol Monitor 8520 for measuring PM2.5 concentrations and meteorological parameters. Microbial concentrations showed a significant difference between various sites over the study period with averages of 569.57?±?312.64 and 482.73?±?242.86 CFU/M3 for bacteria and fungi, respectively. The air temperature had a significant effect on the concentration of both airborne bacteria and fungi. A significant positive correlation between relative humidity and fungi but no correlation between relative humidity and bacteria concentrations were observed. The average airborne PM2.5 concentrations of all sites among the study period was 93.24?±?116.72 μg/m3. The atmospheric bacterial and fungal communities were strongly positively correlated with the ambient PM2.5 level. The levels of airborne bacteria and fungi along with PM2.5 in the air of the city were relatively higher than the recommended levels. Therefore, the best course of action is needed to control emission sources. Further studies are also needed to evaluate the clinical analysis of the health effects of exposure to these pollutants. 相似文献
20.
In a combined field and laboratory study in the southwest of Burkina Faso, we quantified soil-atmosphere N 2O and NO exchange. N 2O emissions were measured during two field campaigns throughout the growing seasons 2005 and 2006 at five different experimental
sites, that is, a natural savanna site and four agricultural sites planted with sorghum ( n = 2), cotton and peanut. The agricultural fields were not irrigated and not fertilized. Although N 2O exchange mostly fluctuated between −2 and 8 μg N 2O–N m −2 h −1, peak N 2O emissions of 10–35 μg N 2O–N m −2 h −1 during the second half of June 2005, and up to 150 μg N 2O–N m −2 h −1 at the onset of the rainy season 2006, were observed at the native savanna site, whereas the effect of the first rain event
on N 2O emissions at the crop sites was low or even not detectable. Additionally, a fertilizer experiment was conducted at a sorghum
field that was divided into three plots receiving different amounts of N fertilizer (plot A: 140 kg N ha −1; plot B: 52.5 kg N ha −1; plot C: control). During the first 3 weeks after fertilization, only a minor increase in N 2O emissions at the two fertilized plots was detected. After 24 days, however, N 2O emission rates increased exponentially at plot A up to a mean of 80 μg N 2O–N m −2 h −1, whereas daily mean values at plot B reached only 19 μg N 2O–N m −2 h −1, whereas N 2O flux rates at plot C remained unchanged. The calculated annual N 2O emission of the nature reserve site amounted to 0.52 kg N 2O–N ha −1 a −1 in 2005 and to 0.67 kg N 2O–N ha −1 a −1 in 2006, whereas the calculated average annual N 2O release of the crop sites was only 0.19 kg N 2O–N ha −1 a −1 and 0.20 kg N 2O–N ha −1 a −1 in 2005 and 2006, respectively. In a laboratory study, potential N 2O and NO formation under different soil moisture regimes were determined. Single wetting of dry soil to medium soil water
content with subsequent drying caused the highest increase in N 2O and NO emissions with maximum fluxes occurring 1 day after wetting. The stimulating effect lasted for 3–4 days. A weaker
stimulation of N 2O and NO fluxes was detected during daily wetting of soil to medium water content, whereas no significant stimulating effect
of single or daily wetting to high soil water content (>67% WHC max) was observed. This study demonstrates that the impact of land-use change in West African savanna on N trace gas emissions
is smaller—with the caveat that there could have been potentially higher N 2O and NO emissions during the initial conversion—than the effect of timing and distribution of rainfall and of the likely
increase in nitrogen fertilization in the future. 相似文献
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