Postfire nitrogen balance of Mediterranean shrublands: Direct combustion losses versus gaseous and leaching losses from the postfire soil mineral nitrogen flush

Fire is a major factor controlling global carbon (C) and nitrogen (N) cycling. While direct C and N losses caused by combustion have been comparably well established, important knowledge gaps remain on postfire N losses. Here, we quantified both direct C and N combustion losses as well as postfire gaseous losses (N₂O, NO and N₂) and N leaching after a high‐intensity experimental fire in an old shrubland in central Spain. Combustion losses of C and N were 9.4 Mg C/ha and 129 kg N/ha, respectively, representing 66% and 58% of initial aboveground vegetation and litter stocks. Moreover, fire strongly increased soil mineral N concentrations by several magnitudes to a maximum of 44 kg N/ha 2 months after the fire, with N largely originating from dead soil microbes. Postfire soil emissions increased from 5.4 to 10.1 kg N ha^?1 year^?1 for N₂, from 1.1 to 1.9 kg N ha^?1 year^?1 for NO and from 0.05 to 0.2 kg N ha^?1 year^?1 for N₂O. Maximal leaching losses occurred 2 months after peak soil mineral N concentrations, but remained with 0.1 kg N ha^?1 year^?1 of minor importance for the postfire N mass balance. ¹⁵N stable isotope labelling revealed that 33% of the mineral N produced by fire was incorporated in stable soil N pools, while the remainder was lost. Overall, our work reveals significant postfire N losses dominated by emissions of N₂ that need to be considered when assessing fire effects on ecosystem N cycling and mass balance. We propose indirect N gas emissions factors for the first postfire year, equalling to 7.7% (N₂‐N), 2.7% (NO‐N) and 5.0% (N₂O‐N) of the direct fire combustion losses of the respective N gas species.     

Mineralization and gaseous losses of nitrogen from urea and ammonium sulphate in salt-affected soils

Summary An incubation study on mineralization and gaseous losses of nitrogen was conducted on three soils with increasing levels (1.1 to 50 mmhos/cm) of salinity and two levels of urea and ammonium sulphate upto 6 weeks. Mineralization of nitrogen increased with time and decreased with the increase of salinity. It was more from ammonium sulphate than urea, and relatively more from the lower dose. The gaseous losses of NH₄-N increased with salinity. About 35±5 per cent of added N was lost in the gaseous form at maximum (ECe=45 to 50 mmhos/cm) salinity and losses were more from light than heavier soils. Salinity and pH, both were correlated negatively with the N mineralisation and positively with the gaseous losses of ammonia in these salt-affected soils. re]19751105     

Exchange of gaseous nitrogen compounds between agricultural systems and the atmosphere

Crop and livestock agricultural production systems are important contributors to local, regional and global budgets of NH₃, NO_x (NO + NO₂) and N₂O. Emissions of NH₃ and NO_x (which are biologically and chemically active) into the atmosphere serve to redistribute fixed N to local and regional aquatic and terrestrial ecosystems that may otherwise be disconnected from the sources of the N gases. The emissions of NO_x also contribute to local elevated ozone concentrations while N₂O emissions contribute to global greenhouse gas accumulation and to stratospheric ozone depletion.Ammonia is the major gaseous base in the atmosphere and serves to neutralize about 30% of the hydrogen ions in the atmosphere. Fifty to 75% of the 55 Tg N yr^–1 NH₃ from terrestrial systems is emitted from animal and crop-based agriculture from animal excreta and synthetic fertilizer application. About half of the 50 Tg N yr^–1 of NO_x emitted from the earth surface annually arises from fossil fuel combustion and the remainder from biomass burning and emissions from soil. The NO_x emitted, principally as nitric oxide (NO), reacts rapidly in the atmosphere and in a complex cycle with light, ozone and hydrocarbons, and produces nitric acid and particulate nitrate. These materials can interact with plants and the soil locally or be transported form the site and interact with atmospheric particulate to form aerosols. These salts and aerosols return to fertilize terrestrial and aquatic systems in wet and dry deposition. A small fraction of this N may be biologically converted to N₂O. About 5% of the total atmospheric greenhouse effect is attributed to N₂O from which 70% of the annual global anthropogenic emissions come from animal and crop production.The coupling of increased population with a move of a large sector of the world population to diets that require more energy and N input, will lead to continued increases in anthropogenic input into the global N cycle. This scenario suggests that emissions of NH₃, NO_x and N₂O from agricultural systems will continue to increase and impact global terrestrial and aquatic systems, even those far removed from agricultural production, to an ever growing extent, unless N resources are used more efficiently or food consumption trends change.     

利用CRISPR-Cas系统防控细菌耐药性的研究进展

细菌多重耐药是医药健康、农林牧渔、生态环境等多领域共同面临的全球性挑战.抗生素耐药基因跨物种跨区域传播是导致细菌多重耐药形成的重要原因.然而,目前尚无有效方案解决日益严峻的细菌多重耐药问题.由规律成簇间隔短回文重复序列和与之相关的蛋白组成的CRISPR-Cas系统,可靶向切割进入细菌的外源核酸,具有防控耐药基因转移导致...     

我国稻田氮磷流失现状及影响因素研究进展

水稻是我国主要的粮食作物,分析现阶段我国稻田氮磷流失现状及影响因素,对明确不同区域水稻化肥减施潜力具有重要意义.本研究对我国主要稻区地表径流氮磷流失现状特征和降雨、种植模式、栽培技术、施肥管理、水分管理方式及其他影响因素进行了总结.六大稻区全氮(TN)、全磷(TP)径流损失量范围分别在5.09～21.32和0.70～3.22 kg·hm^-2,均以华南双季稻区最高,TN径流损失量以华北单季稻区最低,TP径流损失量以西南高原单双季稻区最低.各稻区农户习惯施肥的水稻田田面水TN、TP峰值普遍高于径流水.水稻施肥后一周内为氮磷流失高峰期.与优化施肥相比,农户习惯施肥仍具有20%左右的氮磷减施潜力.各因素中,降雨和施肥管理是影响稻田径流氮磷流失的主要因素,而施肥管理和水分管理则最具可控性,具体调控措施包括化肥减量、施用新型肥料、有机肥代替化肥和节水灌溉等.整体上我国稻田氮磷流失风险在南方更突出.应以资源高效利用模式进行水稻种植以降低养分流失风险.未来研究应侧重稻田面源污染监测、氮磷流失风险评估、氮磷流失特征和机理、化肥减施增效新技术等方向.     

养殖环境中抗生素抗性基因的研究进展

抗性基因在环境中的垂直及水平传播,致使抗生素耐药性成为危及人类和动物生命健康的全球性问题。动物源食品是中国美食不可或缺之物,而由于抗生素超用与滥用等行为让公众不得不关注动物源食品源头——养殖场的抗生素抗性基因环境安全问题。本文综述了养殖环境中抗生素抗性基因的研究进展,分析了养殖环境中抗生素抗性基因产生原因、传播途径以及影响因素,介绍了现有风险评估方法和控制技术,并对今后养殖环境中抗生素抗性基因的控制策略、技术及研究方向提出了建议。     

放牧家畜排泄物N转化研究进展

放牧家畜排泄物氮转化是草原生态系统氮循环的关键。自 2 0世纪 70年代以来 ,以提高氮利用效率和减少温室气体排放为目的的家畜排泄物氮转化的研究越来越受到人们的重视。放牧家畜排泄物氮的转化研究主要包括 3个方面 :氮的矿化、硝化与反硝化 ,氮的氨化。家畜粪氮矿化速度慢 ,持续时间长 ;尿氮矿化速度快 ,持续时间短。氮矿化与家畜排泄物 C∶ N比、木质素/氮素比、木质素含量和纤维素含量呈负相关关系 ,而与全氮含量和水溶性氮含量呈正相关 ;土壤动物和微生物可以显著促进氮的矿化过程 ;高温和相对干燥、砂质土壤较壤土和粘土有利于氮的矿化。 4～ 4 0℃氮硝化作用与温度呈正相关 ;硝化作用的底物和产物浓度、土壤溶液渗透压和氯化物浓度的增加对硝化作用有强烈的抑制效应 ;p H6 .0～ 8.0条件下硝化作用强度随着土壤p H值的升高而增加 ,而 p H值高于 8.0或低于 6 .0时硝化作用受到抑制 ;硝化作用与土壤氧气含量呈正相关关系 ,而与土壤含水量呈负相关 ;温暖湿润较干燥炎热的气候条件有利于硝化过程的进行。反硝化作用与土壤氧气浓度呈负相关关系 ,而与土壤含水量和可利用有机碳含量呈正相关 ;0～ 6 5℃反硝化作用强度随温度升高而增大 ,10～ 35℃条件下温度成为影响反硝化作用的关键因素 ;反硝化作用在     

Nitrogen budget and gaseous nitrogen loss in a tropical agricultural watershed

Although agricultural systems in tropical monsoon Asia play a central role in the global nitrogen (N) cycle, details of the N cycle in this region on a watershed scale remain unclear. This study quantified the N budget in a tropical watershed of 221 km² on Java Island, where paddy fields cover 28% of the land, by conducting field surveys. The amount of net biochemical gaseous N loss to the atmosphere (X _GB ), which is generally difficult to determine, was calculated as the residual of the N balance. Assuming that NH₃ volatilization balances deposition, and hence subtracting NH₄–N from the N import with atmospheric deposition, the average total import and export of N per year was found to be 46.5 kg ha⁻¹ year⁻¹ over the watershed. Of this, 71% was imported as fertilizer (M _F ) and 29% with atmospheric deposition (M _AD ). On the export side, 42% was lost as X _GB , 37% with incineration of rice residues and wood fuel (X _GI ), 13% with river discharge (X _D ) and 9% with rice surplus export (X _R ). A large portion of X _GB , and consequently, a small portion of X _D could be explained by the high rate of denitrification resulting from the high temperature and humid climate, and are thought to be common features of tropical watersheds where paddy fields are found.     

cGAS-STING信号通路在畜禽疾病中的研究进展

cGAS-STING信号通路是一种细胞内DNA感受器,可以识别自身病变或外部进入细胞质中的双链DNA。其不仅与肿瘤、病毒和细菌感染及自身免疫系统疾病密切相关,而且在非特异性免疫系统中发挥重要作用。截至目前,国内外对于cGAS-STING信号通路的研究主要集中在哺乳动物肿瘤相关性疾病及与先天性免疫系统相关的疾病中,而通路对畜禽疾病调控的影响机制非常重要。本文以cGAS-STING信号通路在宿主受到病原感染中发挥的作用为切入点,对其在不同畜禽病原感染中的调控作用进行综合论述,以期为畜禽疾病的防控提供理论依据和参考。     

Main animal welfare problems in ruminant livestock during preslaughter operations: a South American view

Animals destined for meat production are usually exposed to many stressful conditions during production and particularly during preslaughter operations. Handling animals on farm, loading into and unloading from vehicles, transportation, passing through livestock markets, fasting, lairage and stunning can all affect their welfare. How badly welfare can be affected will depend on both the intrinsic factors of the specific type of animal involved and the extrinsic factors of the environment where those animals live or are being handled, including the animal handlers. In South America (SA), it has been part of a strategy for improving animal welfare (AW) to address not only ethical aspects, but to emphasize the close relationship existing between handling ruminants preslaughter and the quantity and quality of the meat they produce. This has resulted not only in improvements in AW, but has also brought economic rewards to producers which in turn can lead to higher incomes for them and hence better human welfare. For producers with a high number of animals, considering AW during production and preslaughter operations can determine the possibility of exporting and/or getting better prices for their products. At smallfarmer level, particularly in some less developed countries, where human welfare is impaired, using this strategy together with education has also been relevant. It is important that education and training in AW are done not only considering global knowledge, but also including specific geographical and climatic characteristics of each country and the cultural, religious and socio-economical characteristics of its people; therefore, research within the context of each country or region becomes relevant. The aim of this review was to show the results of research dealing with AW of ruminant livestock in Chile and some other SA countries. Some of the main problems encountered are related to lack of proper infrastructure to handle animals; long distance transport with high stocking densities in the larger countries; long fasting times due to animals passing through livestock markets and dealers; bad handling of animals by untrained personnel in these and other premises; and finally the lack of knowledge and skills by operators in charge of stunning procedures. Interventions at these stages have considered training animal handlers and transporters by showing them the consequences of bad handling with audiovisual material prepared on site. Research results have helped to improve AW and support the development of new legislation or to make changes in the existent legislation related to AW.     

Quantifying livestock responses for heat stress management: a review

 Hot weather challenges livestock production but technology exists to offset the challenge if producers have made appropriate strategic decisions. Key issues include understanding the hazards of heat stress, being prepared to offer relief from the heat, recognizing when an animal is in danger, and taking appropriate action. This paper describes our efforts to develop biological response functions; assesses climatic probabilities and performs associated risk analyses; provides inputs for computer models used to make environmental management decisions; and evaluates threshold temperatures as estimates of critical temperature limits for swine, cattle and sheep. Received: 3 September 1998/Accepted: 5 October 1998     

Effect of ambient temperature on losses of volatile nitrogen compounds from stored laying hen manure

Eight one tonne lots of laying hen manure were stored in individual, environmentally controlled chambers for 18-weeks at one of four constant temperatures: 12, 15, 20 and 25 degrees C. The losses of volatile nitrogen compounds, ammonia, and changes in dry matter and pH were measured during the storage period. There was a linear (P < 0.001) loss of nitrogen from the manure over the 18-week storage period. This loss represented approximately 60% of the initial nitrogen present in the manure. The rate of nitrogen loss increased non-linearly (P < 0.05) with increasing storage temperature. Poultry housing systems that provide low temperature storage of manure are recommended to reduce the volatile nitrogen losses from egg-laying enterprises.     

Indicators used in livestock to assess unconsciousness after stunning: a review

Assessing unconsciousness is important to safeguard animal welfare shortly after stunning at the slaughter plant. Indicators that can be visually evaluated are most often used when assessing unconsciousness, as they can be easily applied in slaughter plants. These indicators include reflexes originating from the brain stem (e.g. eye reflexes) or from the spinal cord (e.g. pedal reflex) and behavioural indicators such as loss of posture, vocalisations and rhythmic breathing. When physically stunning an animal, for example, captive bolt, most important indicators looked at are posture, righting reflex, rhythmic breathing and the corneal or palpebral reflex that should all be absent if the animal is unconscious. Spinal reflexes are difficult as a measure of unconsciousness with this type of stunning, as they may occur more vigorous. For stunning methods that do not physically destroy the brain, for example, electrical and gas stunning, most important indicators looked at are posture, righting reflex, natural blinking response, rhythmic breathing, vocalisations and focused eye movement that should all be absent if the animal is unconscious. Brain stem reflexes such as the cornea reflex are difficult as measures of unconsciousness in electrically stunned animals, as they may reflect residual brain stem activity and not necessarily consciousness. Under commercial conditions, none of the indicators mentioned above should be used as a single indicator to determine unconsciousness after stunning. Multiple indicators should be used to determine unconsciousness and sufficient time should be left for the animal to die following exsanguination before starting invasive dressing procedures such as scalding or skinning. The recording and subsequent assessment of brain activity, as presented in an electroencephalogram (EEG), is considered the most objective way to assess unconsciousness compared with reflexes and behavioural indicators, but is only applied in experimental set-ups. Studies performed in an experimental set-up have often looked at either the EEG or reflexes and behavioural indicators and there is a scarcity of studies that correlate these different readout parameters. It is recommended to study these correlations in more detail to investigate the validity of reflexes and behavioural indicators and to accurately determine the point in time at which the animal loses consciousness.     

Postanthesis remobilisation and losses of nitrogen in wheat in relation to applied nitrogen

A ¹⁵N leaf feeding technique was used to measure the extent of remobilisation and loss of nitrogen (N) that had been accumulated prior to anthesis in wheat plants that received three rates of N fertilizer. Uptake of postanthesis N to the heads was reduced as the quantity of applied N was increased. This reduction of postanthesis N uptake did not affect the quqntity of N in the heads because the loss of preanthesis accumulated N was reduced and the extent of remobilised preanthesis N increased at higher rates of N application. At the lowest rate of N application the increase in ¹⁵N in the heads of fertile shoots arose chiefly from the remobilisation of N in the stem supporting the head. At higher rates of N application this source of N was increasingly supplemented by N remobilised from infertile tillers and roots.     

Strategies for farmers and policy makers to control nitro-gen losses whilst maintaining crop production

The nitrogen (N) cycle is essentially 'leaky'. The losses of small amounts of nitrate to waters and of ammonia and nitrous oxide to the atmosphere are a part of the global biogeo-chemical N cycle. However, intensive agricultural production, industry and vehicle use have more than doubled the amount of 'reactive' N in the environment, resulting in eutrophication, ecosystem change and health concerns. Research has identified agricultural practices that cause large losses of N and, in some cases, developed solutions. This paper discusses the problems of maintaining productivity while reducing N losses, compares conventional with low input (integrated) and organic farming systems, and discusses wider options. It also looks at the need to integrate studies on N with other environmental impacts, set in the context of the whole farm system, to provide truly sustainable agricultural systems.