Effects of urine on soil microbial biomass,methanogenesis, nitrification and denitrification in grassland soils

Urine was added under controlled conditions to intact turfs taken from long-term permanent pasture on clay loam and sandy loam soils in South West England. Methane exchanges were small (<+/−0.03 μg CH₄ m^-2 min^-1) and overall absorption equalled or exceeded emission in both soils. On the clay loam, wetting with water or urine increased soil microbial biomass C and N contents by about 20% but there was no specific effect of urine. Urine, however, caused an increase in soil respiration of >50% and the average increase was greater for cow's urine (30.8 mg CO₂ m^-2 min^-1) than for an artificial urine (20.1 mg CO₂ m^-2 min^-1). Emissions of nitric and nitrous oxides following urine application were substantial (on average 0.36 μg NO-N and 29 μg N₂O-N m^-2 min^-1) but short lived (<40 days). The high levels of ammonium found in the urine treated soils (>200 mg NH₄ ⁺-N kg^-1) were nitrified to nitrate over a period of 42 days. Qualitative changes in the soil microbial biomass were evidently not related to biomass size. Relationships between trace gas emissions and soil processes are discussed. ei]Section editor: R Merckx     

Denitrification and N2O emission from urine-affected grassland soil

Denitrification and N₂O emission rates were measured following two applications of artificial urine (40 g urine-N m^–2) to a perennial rye-grass sward on sandy soil. To distinguish between N₂O emission from denitrification or nitrification, urine was also applied with a nitrification inhibitor (dicyandiamide, DCD). During a 14 day period following each application, the soil was frequently sampled, and incubated with and without acetylene to measure denitrification and N₂O emission rates, respectively.Urine application significantly increased denitrification and N₂O emission rates up to 14 days after application, with rates amounting to 0.9 and 0.6 g N m^–2 day^–1 (9 and 6 kg N ha^–1 day^–1), respectively. When DCD was added to the urine, N₂O emission rates were significantly lower from 3 to 7 days after urine application onwards. Denitrification was the main source of N₂O immediately following each urine application. 14 days after the first application, when soil water contents dropped to 15% (v/v) N₂O mainly derived from nitrification.Total denitrification losses during the 14 day periods were 7 g N m^–2, or 18% of the urine-N applied. Total N₂O emission losses were 6.5 and 3 g N m^–2, or 16% and 8% of the urine-N applied for the two periods. The minimum estimations of denitrification and N₂O emission losses from urine-affected soil were 45 to 55 kg N ha^–1 year^–1, and 20 to 50 kg N ha^–1 year^–1, respectively.     

Nitrogen losses due to denitrification from cattle slurry injected into grassland soil with and without a nitrification inhibitor

Injection of cattle slurry into a grassland soil decreases NH₃ volatilisation and increases N utilisation by the sward, but may also increase denitrification losses. Denitrification rates were measured using a soil core incubation technique involving acetylene inhibition, following injection of cattle slurry (67 t ha^–1) into a grassland soil. The slurry was injected, either with or without a nitrification inhibitor (DCD), on 8 December 1989. Two-weekly measurements were carried out up to 18 weeks after injection. Compared to the control plot, denitrification rates were significantly higher after slurry injection. Addition of DCD to the slurry almost eliminated this effect. Estimated N-losses during 18 weeks after injection were 0.9 (control), 4.1 (+DCD), and 13.7 (-DCD) kg N ha^–1. Denitrification losses were 7% of the injected NH₄-N and decreased to 2% of the injected NH₄-N when DCD was added. Denitrification could account for about 19% of the difference in apparent recovery of N from slurry injected with and without DCD. The results suggested that considerable amounts of NO₃ ^– were lost due to leaching.     

Simultaneous nitrification and denitrification in a mixed methanotrophic culture

Simultaneous nitrification and denitrification using a mixed methanotrophic culture was investigated. When both NO₃ ^–-N (108 mg l^–1) and NH₃-N (59 mg l^–1) were added into batch reactors, nitrate removal was complete within 10 h at the rate of 47 mg NO₃ ^–-N g VSS^–1 day^–1 when dissolved oxygen (DO) concentration was maintained at 2 mg DO l^–1. Ammonia removal started simultaneously with nitrate removal at a slower rate of 14 NH₃-N g VSS^–1 day^–1. No significant accumulation of nitrite or nitrate during ammonia utilization suggested the occurrence of simultaneous nitrification and denitrification.     

Comparison of soil nitrogen mineralization and nitrification in a mixed grassland and forested ecosystem in central Taiwan

We used the buried bag incubation method to study temporal patterns of net N mineralization and net nitrification in soils at Ta-Ta-Chia forest in central Taiwan. The site included a grassland zone, (dominant vegetation consists of Yushania niitakayamensis and Miscanthus transmorrisonensis Hayata) and a forest zone (Tsuga chinensis var. formosana and Yushania niitakamensis). In the grassland, soil concentration NH₄ ⁺ in the organic horizon (0.1–0.2 m) ranged from 1.0 to 12.4 mg N kg^–1 soil and that of NO₃ ^– varied from 0.2 to 2.1 mg N kg^–1 soil. In the forest zone, NH₄ ⁺ concentration was between 2.8 and 25.0 mg N kg^–1 soil and NO₃ ^–varied from 0.2 to 1.3 mg N kg^–1 soil. There were lower soil NH₄ ⁺ concentrations during the summer than other seasons. Net N mineralization was higher during the summer while net nitrification rates did not show a distinct seasonal pattern. In the grassland, net N mineralization and net nitrification rates were between –0.1 and 0.24 and from –0.04 to 0.04 mg N kg^–1 soil day^–1, respectively. In the forest zone, net N mineralization rates were between –0.03 and 0.45 mg N kg^–1 soil day^–1 and net nitrification rates were between –0.01 and 0.03 mg N kg^–1 soil day^–1. These differences likely result from differing vegetation communities (C₃ versus C₄ plant type) and soil characteristics.     

Mixed culture of nitrifying bacteria and denitrifying bacteria for simultaneous nitrification and denitrification

A mixed culture containing nitrifying bacteria and denitrifying bacteria was investigated for aerobic simultaneous nitrification and denitrification. A mixture of NaHCO₃ and CH₃COONa was selected as the appropriate carbon source for cell growth and nitrogen removal, the concentrations of carbon and nitrogen sources were also examined. Ammonia could be oxidized aerobically to nitrite by the mixed culture, and the intermediate nitrite was then reduced to dinitrogen gas. No nitrite was detected during the process. 0.212 g of ammonia/l could be removed in 30 h and nitrate could not be utilized aerobically by the mixed culture. Nitrite could be degraded aerobically as well as anaerobically. Very little ammonia was degraded anaerobically, but the ability to degrade ammonia could be recovered even after oxygen had been supplied for 42 h.     

华北盐渍化草地土壤净氮矿化速率对不同水平氮添加的响应

对于养分贫瘠的盐渍化草地生态系统, 大气氮沉降如何影响土壤氮循环过程是一个目前尚未解决的问题。该研究在位于华北地区山西省右玉县境内的盐渍化草地建立了一个模拟氮沉降的试验平台, 设置8个氮添加水平, 分别为0、1、2、4、8、16、24、32 g·m^-2·a^-1 (N0、N1、N2、N4、N8、N16、N24、N32), 生长季5-9月, 每月月初以喷施的方式等量添加NH₄NO₃。从2017年5月到2019年10月, 运用顶盖PVC管法每月一次进行净氮矿化速率的测定同时计算了净氮矿化速率对不同水平氮添加的敏感性。主要结果表明: (1)高水平氮添加(N16、N24、N32)显著增加土壤无机氮库; (2)该盐渍化草地土壤氮矿化以硝化作用为主, 经过3年氮添加以后, 高氮添加(N24、N32)显著促进了土壤净硝化速率, 并且不同氮添加水平在不同的月份和年份中表现出差异性响应; (3)不同氮添加水平对土壤净氮矿化敏感性的影响在不同降水年份差异显著, 短期低水平氮添加提高了土壤净氮矿化的敏感性, 而高水平氮添加降低土壤净氮矿化敏感性; (4)盐渍化草地土壤净氮矿化速率与土壤温度和水分呈正相关关系, 与土壤pH呈负相关关系。因此, 在当前氮沉降增加的背景下, 北方盐渍化草地土壤氮矿化速率对低氮添加的敏感性较高, 结合氮沉降的特点, 未来模型预测应该同时考虑氮沉降对盐渍化草地的可能影响。     

Challenges for simultaneous nitrification, denitrification, and phosphorus removal in microbial aggregates: mass transfer limitation and nitrous oxide production

The microbial community composition and activity was investigated in aggregates from a lab-scale bioreactor, in which nitrification, denitrification and phosphorus removal occurred simultaneously. The biomass was highly enriched for polyphosphate accumulating organisms facilitating complete removal of phosphorus from the bulk liquid; however, some inorganic nitrogen still remained at the end of the reactor cycle. This was ascribed to incomplete coupling of nitrification and denitrification causing NO(3)(-) accumulation. After 2 h of aeration, denitrification was dependent on the activity of nitrifying bacteria facilitating the formation of anoxic zones in the aggregates; hence, denitrification could not occur without simultaneous nitrification towards the end of the reactor cycle. Nitrous oxide was identified as a product of denitrification, when based on stored PHA as carbon source. This observation is of critical importance to the outlook of applying PHA-driven denitrification in activated sludge processes.     

Annual nitrous oxide flux and soil nitrogen characteristics in sagebrush steppe ecosystems

Soil nitrogen transformations and nitrous oxide fluxes were measured in a range of sagebrush steppe ecosystems in south-central Wyoming. Net nitrate production, measured in laboratory incubations, was highest in the ecosystem type dominated by Artemisia tridentata ssp. vaseyana, especially early in the growing season. Fluxes of nitrous oxide, measured in closed chambers and analyzed by gas chromatography, also tended to be higher in the same type, but only for short periods in the spring. Thereafter, all nitrous oxide fluxes were low and did not differ consistently among types. Estimated average annual fluxes for three Artemisia ecosystem types (dominated by Artemisia tridentata ssp. vaseyana, Artemisia tridentata ssp. wyomingensis, and Artemisia nova) were 0.32, 0.23 and 0.13 kg N₂O-N ha^–1 y^–1 repsectively. Average annual flux, weighted by the areal extent of these and other vegetation types in the region, was approximately 0.21 kg N₂O-N ha^–1y^–1. Assuming this landscape is representative of sagebrush steppe, we calculate a flux of 9.5 × 10⁹ g y^–1 of N₂O-N from U.S. sagebrush steppe, and a flux of 1.1 × 10¹¹ g y^–1 of N₂0-N from analogous desert and semi-desert shrublands of the world.     

Nitrous oxide production, its source and distribution in urine patches on grassland on peat soil

Urine patches are considered to be important sites for nitrous oxide (N₂O) production through nitrification and denitrification due to their high concentration of nitrogen (N). The aim of the present study was to determine the microbial source and size of production of N₂O in different zones of a urine patch on grassland on peat soil. Artificial urine was applied in elongated patches of 4.5 m. Four lateral zones were distinguished and sampled for four weeks using an intact soil core incubation method. Incubation of soil cores took place without any additions to the headspace to determine total N₂O production, with acetylene addition to determine total denitrification (N₂O+N₂), and with methyl fluoride to determine the N₂O produced through denitrification.Nitrous oxide production was largest in the centre and decreased towards the edge of the patch. Maximum N₂O production was about 50 mg N m^–2 d^–1 and maximum denitrification activity was 70 mg N m^–2 d^–1. Nitrification was the main N₂O producing process. Nitrous oxide production through denitrification was only of significance when denitrification activity was high. Total N loss through nitrification and denitrification over 31 days was 4.1 g N per patch which was 2.2% of the total applied urine-N.     

Role of nitrification and denitrification for NO metabolism in soil

Release and uptake of NO was measured in a slightly alkaline (pH 7.8) and an acidic (pH 4.7) cambisol. In the alkaline soil under aerobic conditions, NO release was stimulated by ammonium and inhibited by nitrapyrin. Nitrate accumulated simultaneously and was also inhibited by nitrapyrin.¹⁵NO was released after fertilization with¹⁵NH₄NO₃ but not with NH₄ ¹⁵NO₃. The results indicate that in aerobic alkaline cambisol NO was mainly produced during nitrification of ammonium. The results were different under anaerobic conditions and also in the acidic cambisol. There, NO release was stimulated by nitrate and not by ammonium, and was inhibited by chlorate and not by nitrapyrin indicating that NO production was exclusively due to reduction of nitrate. The results were confirmed by¹⁵NO being released mainly from NH₄ ¹⁵NO₃ rather than from¹⁵NH₄NO₃. The observed patterns of NO release were explained by the NO production processes being stimulated by either ammonium or nitrate in the two different soils, whereas the NO consumption processes being only stimulated by nitrate. NO release was larger than N₂O release, but both were small compared to changes in concentrations of soil ammonium or nitrate.(*request for offprints)     

Predicting in situ soil N2O emission using NOE algorithm and soil database

This paper presents a new algorithm, Nitrous Oxide Emission (NOE) for simulating the emission of the greenhouse gas N₂O from agricultural soils. N₂O fluxes are calculated as the result of production through denitrification and nitrification and reduction through the last step of denitrification. Actual denitrification and nitrification rates are calculated from biological parameters and soil water‐filled pore space, temperature and mineral nitrogen contents. New suggestions in NOE consisted in introducing (1) biological site‐specific parameters of soil N₂O reduction and (2) reduction of the N₂O produced through nitrification to N₂ through denitrification. This paper includes a database of 64 N₂O fluxes measured on the field scale with corresponding environmental parameters collected from five agricultural situations in France. This database was used to test the validity of this algorithm. Site per site comparison of simulated N₂O fluxes against observed data leads to mixed results. For 80% of the tested points, measured and simulated fluxes are in accordance whereas the others resulted in an important discrepancy. The origin of this discrepancy is discussed. On the other hand, mean annual fluxes measured on each site were strongly correlated to mean simulated annual fluxes. The biological site‐specific parameter of soil N₂O reduction introduced into NOE appeared particularly useful to discriminate the general level of N₂O emissions from site to site. Furthermore, the relevance of NOE was confirmed by comparing measured and simulated N₂O fluxes using some data from the US TRAGNET database. We suggest the use of NOE on a regional scale in order to predict mean annual N₂O emissions.     

四种温带森林土壤氮矿化与硝化时空格局

利用PVC管原位培养连续取样法测定了东北地区4种具有代表性的森林生态系统(硬阔叶林、蒙古栎林、红松林、落叶松林)土壤氮素矿化、硝化的时间动态及氮矿化的空间分布格局.结果表明:4种森林土壤氮素矿化存在明显的时空变异.蒙古栎和红松林土壤在6月份表现出强烈的氮矿化和硝化作用,而硬阔叶林及落叶松林7月份氮素矿化强烈.4种森林生态系统上层土壤的氮净矿(硝)化率显著高于下层土壤.4种林型土壤的硝化过程在氮矿化过程中占有重要地位,其NO-3-N在无机氮中的比例分别为:79.9%～91.1%(硬阔叶林)、50.7%～80.5%(蒙古栎林)、54.1%～92.0%(红松林)、63.7%～86.5%(落叶松林).生态系统构成决定了土壤氮素的矿化能力.阔叶林和针阔混交林生态系统矿化率大于纯针叶林生态系统.硬阔叶林、红松林、蒙古栎林、落叶松林的平均净矿化率分别为:(0.58±0.01) mg · kg-1 · d-1、(0.47±0.19) mg · kg-1 · d-1、(0.39±0.11) mg · kg-1 · d-1和(0.23±0.06) mg · kg-1 · d-1.4种林型氮素矿化作用与地下5 cm温度呈正相关,并受土壤表层 (0～10 cm)水分显著影响.土壤微生物量氮与土壤氮矿化呈显著正相关.     

Improved simultaneous nitrification and denitrification in a single reactor by using two different immobilization carriers with specific oxygen transfer characteristics

To maximize nitrogen utilization rates during nitrification and denitrification in a simultaneous reaction for direct nitrogen removal from ammonia–nitrogen in a single reactor, two different carriers were applied that immobilized nitrifiers and denitrifiers separately. With the optimized DO concentration and mixing ratio of immobilization carriers, ammonium–nitrogen was successfully removed as designed until the middle phase of treatment where nitrogen removal rate was higher than 83% of the theoretical value, although an imbalance between nitrification and denitrification occurred at a later phase of treatment where residual nitrate–nitrogen concentration was less than 2 mg/l. The new approach using two different carriers to immobilize nitrifiers and denitrifiers separately was proved useful for controlling both nitrification and denitrification rates, enabling the utilization of maximum treatment ability of both nitrifiers and denitrifiers in a single reactor for direct nitrogen removal from ammonium–nitrogen.     

Effect of sludge age on simultaneous nitrification and denitrification in membrane bioreactor

This study evaluated the effect of sludge age on simultaneous nitrification and denitrification in a membrane bioreactor treating black water. A membrane bioreactor with no separate anoxic volume was operated at a sludge age of 20 days under low dissolved oxygen concentration of 0.1-0.2 mg/L. Its performance was compared with the period when the sludge age was adjusted to 60 days. Floc size distribution, apparent viscosity, and nitrogen removal differed significantly, together with different biomass concentrations: nitrification was reduced to 40% while denitrification was almost complete. Modelling indicated that both nitrification and denitrification kinetics varied as a function of the sludge age. Calibrated values of half saturation coefficients were reduced when the sludge age was lowered to 20 days. Model simulation confirmed the validity of variable process kinetics for nitrogen removal, specifically set by the selected sludge age.     

Effect of oxic and anoxic conditions on nitrous oxide emissions from nitrification and denitrification processes

A lab-scale sequencing batch reactor fed with real municipal wastewater was used to study nitrous oxide (N(2)O) emissions from simulated wastewater treatment processes. The experiments were performed under four different controlled conditions as follows: (1) fully aerobic, (2) anoxic-aerobic with high dissolved oxygen (DO) concentration, (3) anoxic-aerobic with low DO concentration, and 4) intermittent aeration. The results indicated that N(2)O production can occur from both incomplete nitrification and incomplete denitrification. N(2)O production from denitrification was observed in both aerobic and anoxic phases. However, N(2)O production from aerobic conditions occurred only when both low DO concentrations and high nitrite concentration existed simultaneously. The magnitude of N(2) O produced via anoxic denitrification was lower than via oxic denitrification and required the presence of nitrite. Changes in DO, ammonium, and nitrite concentrations influenced the magnitude of N(2)O production through denitrification. The results also suggested that N(2)O can be produced from incomplete denitrification and then released to the atmosphere during aeration phase due to air stripping. Therefore, biological nitrogen removal systems should be optimized to promote complete nitrification and denitrification to minimize N(2)O emissions.     

不同林龄杉木人工林土壤硝化和反硝化作用

对不同林龄杉木人工林(5、8、21、27和40年生)土壤硝化与反硝化过程及功能微生物丰度进行研究。结果表明: 土壤净硝化速率随林龄的增加波动变化,8、27年生杉木人工林土壤净硝化速率显著低于5、21和40年生。27年生杉木人工林土壤氨氧化古菌(AOA) amoA基因丰度显著低于40年生,其他林龄AOA amoA基因丰度之间无显著差异。不同林龄杉木人工林的氨氧化细菌(AOB) amoA基因丰度、反硝化功能基因丰度以及反硝化潜势均无显著差异。逐步回归分析表明,土壤氨氧化微生物AOA amoA基因丰度受土壤理化性质的影响不显著,土壤总碳和土壤pH是影响AOB丰度的重要因子。反硝化功能基因narG、nirK及nosZ随土壤pH的增加而增加,编码亚硝酸盐还原酶(NIR)的功能基因(nirK、nirS)受土壤总碳的影响。林龄可通过影响AOA amoA基因丰度影响土壤净硝化速率。林龄直接作用于反硝化潜势,或间接影响土壤微生物生物量碳、土壤pH及反硝化功能基因丰度(narG和nirK),进而影响反硝化潜势。相较于反硝化过程,土壤硝化作用及AOA amoA基因丰度对杉木林分发育更加敏感,可适当延长轮伐期以降低土壤硝化作用造成的氮流失风险。     

火烧对草地土壤氮总矿化、硝化及无机氮消耗速率的影响

采用同位素^15N库稀释技术结合扰动较小的管型取样法,测定了羊草草地火烧区与未烧区不同季节土壤氮的总矿化速率、总硝化速率、无机氮消耗速率．结果表明,火烧地的氮总矿化与硝化速率在牧草返青后的4、5月份均高于未烧地,7月份差异不显著,到生长季末的9月份又低于未烧地;火烧地NH^4-N的消耗速率7月份以前均高于未烧地,9月份低于未烧地,N03^--N的消耗4、5份火烧地要高于未烧地,7、9月份又低于未烧地;火烧地土壤NH4^ -N含量在4、5和7月份均高于未烧地,9月份基本没有差别,而N03^--N在4、5月份无大差别,7、9月份高于未烧地．     

Simultaneous nitrification,denitrification, and phosphorus removal in a lab-scale sequencing batch reactor

Simultaneous nitrification and denitrification (SND) via the nitrite pathway and anaerobic-anoxic-enhanced biological phosphorus removal (EBPR) are two processes that can significantly reduce the energy and COD demand for nitrogen and phosphorus removal. The combination of these two processes has the potential of achieving simultaneous nitrogen and phosphorus removal with a minimal requirement for COD. A lab-scale sequencing batch reactor (SBR) was operated in alternating anaerobic-aerobic mode with a low dissolved oxygen (DO) concentration (0.5 mg/L) during the aerobic period, and was demonstrated to accomplish nitrification, denitrification, and phosphorus removal. Under anaerobic conditions, COD was taken up and converted to polyhydroxyalkanoates (PHAs), accompanied by phosphorus release. In the subsequent aerobic stage, PHA was oxidized and phosphorus was taken up to <0.5 mg/L by the end of the cycle. Ammonia was also oxidized during the aerobic period, but without accumulation of nitrite or nitrate in the system, indicating the occurrence of simultaneous nitrification and denitrification. However, off-gas analysis showed that the final denitrification product was mainly nitrous oxide (N(2)O), not N(2). Further experimental results demonstrated that nitrogen removal was via nitrite, not nitrate. These experiments also showed that denitrifying glycogen-accumulating organisms (DGAOs), rather than denitrifying polyphosphate-accumulating organisms (DPAOs), were responsible for the denitrification activity.     

海岸带地区的固氮、氨化、硝化与反硝化特征

海岸带是海洋环境中受人类活动影响最大、生物地球化学循环最为活跃的地区。这一地区氮的生物地球化学循环包括 :生物固氮、有机氮的氨化、氮的硝化、反硝化等 4个主要过程。概括性地介绍了有关这四个过程的发生机制、环境影响因素及研究方法等方面的研究动态、进展、存在的科学问题与今后的研究方向。过去十几年来 ,固氮主要集中在对束毛藻属的研究上 ,其间有两个重要发现 ,一是生物固氮在海洋氮循环中的作用远比人们以前的想象要重要得多 ;二是蓝细菌已经在海洋中存在了 2 0亿年 ,它们有可能调节大气中的 CO2 ,进而影响全球气候。由于有机物的结构千差万别 ,含氮有机物的氨化过程可能是一个简单的矿化反应 ,也有可能是一系列复杂的代谢过程 ,在水解酶的作用下含氮有机物降解为下一级化合物。硝化过程分两步进行 ,氨的硝化为反硝化细菌提供了重要的硝酸盐来源 ,通常采用同位素方法来研究硝化过程。发生在沉积物中的反硝化过程是氮循环的关键步骤 ,反硝化过程一方面减少了海水中初级生产者可利用的氮 ,另一方面产生了终结产物 N2 和 N2 O,而 N2 O是一种温室气体 ,可能影响全球气候变化