Fungal control of nitrous oxide production in semiarid grassland

Fungi are capable of both nitrification and denitrification and dominate the microbial biomass in many soils. Recent work suggests that fungal rather than bacterial pathways dominate N transformation in desert soils. We evaluated this hypothesis by comparing the contributions of bacteria and fungi to N₂O production at control and N fertilized sites within a semiarid grassland in central New Mexico (USA). Soil samples were taken from the rhizosphere of blue grama (B. gracilus) and the microbiotic crusts that grow in open areas between the bunch grasses. Soils incubated at 30% or 70% water holding capacity, were exposed to one of three biocide treatments (control, cycloheximide or streptomycin). After 48 h, N₂O and CO₂ production were quantified along with the activities of several extracellular enzymes. N₂O production from N fertilized soils was higher than that of control soils (165 vs. 41 pmol h⁻¹ g⁻¹), was higher for crust soil than for rhizosphere soil (108 vs. 97 pmol h⁻¹ g⁻¹), and increased with soil water content (146 vs. 60 pmol h⁻¹ g⁻¹). On average, fungicide (cycloheximide) addition reduced N₂O production by 85% while increasing CO₂ production by 69%; bactericide (streptomycin) reduced N₂O by 53% with mixed effects on CO₂ production. N₂O production was significantly correlated with C and N mineralization potential as measured by assays for glycosidic and proteolytic enzymes, and with extractable nitrate and ammonium. Our data indicate that fungal nitrifier denitrification and bacterial autotrophic nitrification dominate N transformation in this ecosystem and that N₂O production is highly sensitive to soil cover, N deposition and moisture.     

植物释放氧化亚氮的研究

氧化亚氮(N_2O)是大气的微量成分之一。多年的测定表明,它在大气中的浓度正以0.2％左右的年增长率在增加。N_2O具有“温室效应”并能催化大气同温层中臭氧保护层的破坏,从而可能带来全球性生态环境的重大变化而受到世人的极大关注。各国科     

Carbon fluxes and species diversity in grazed and fenced typical steppe grassland of Inner Mongolia,China

Aim Grasslands are dominant vegetation of China, support outstanding biodiversity and sequester bulk amount of atmospheric CO₂. These grasslands are highly degraded and fragmented due to remarkable anthropogenic and grazing loads. Chinese Government has made great attempt to restore by grazing exclusion. The relations of carbon fluxes with species composition and diversity in the communities sensitive to grazing by large herbivores are needed to be analysed under the global climate change scenario. The objective of present study was to comprehend the effects of grazing and fencing on the ecosystem structure and function of the typical steppe grassland.     

Identifying sources of nitrous oxide emission in anoxic/aerobic sequencing batch reactors (A/O SBRs) acclimated in different aeration rates

Both long term and batch experiments were carried out to identify the sources of the N₂O emission in anoxic/aerobic sequencing batch reactors (A/O SBRs) under different aeration rates. The obtained results showed that aeration rate has an important effect on the N₂O emission of A/O SBR and most of the N₂O was emitted during the aerobic phase. During the anoxic phase, nitrate ammonification was the major source of N₂O emission while denitrification performed as a sink of N₂O, in all three bioreactors. The N₂O emission mechanisms during the aerobic phase differed with the aeration rate. At low and high aeration rates (Run 1 and Run 3), both coupled-denitrification and nitrifier denitrification were ascribed to be the source of N₂O emission. At mild aeration rate (Run 2), nitrifier denitrification by Nitrosomonas-like ammonia oxidizing-bacterial (AOB) was responsible for N₂O emission while coupled-denitrification turned out to be a sink of N₂O because of the presence of inner anaerobic region in sludge flocs.     

半干旱区生态恢复关键生态系统识别——以内蒙古自治区和林县为例

我国土地退化严重,且大部分发生在干旱半干旱地区.恢复为何种生态系统类型是生态学研究的重要课题.采用生态功能区划,根据各个生态功能区主体生态系统功能,推导发挥此功能的生态系统类型的方法,识别关键生态系统类型.以内蒙古自治区和林县为例,采用文献调研、实地调查、3S技术等方法,在评价该县生态敏感性、生态服务功能重要性的基础上,将该县划分为3个一级生态区,11个二级生态功能区.根据各个生态功能区的主体生态系统服务功能,分析发挥该功能的可能生态系统类型.再根据全国自然植被区划、气候变化趋势模型以及现状植被类型,识别各个生态功能区的关键生态系统类型.     

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.     

Antagonism of nitrous oxide antinociception in mice by intrathecally administered antisera to endogenous opioid peptides

Previously it was demonstrated that nitrous oxide antinociception in the mouse abdominal constriction test is mediated by kappa-opioid receptors. Since nitrous oxide is thought to cause the neuronal release of endogenous opioid peptide to stimulate opioid receptors, this study was designed to identify the opioid peptides involved, especially in the spinal cord, by determining whether nitrous oxide antinociception can be differentially inhibited by intrathecally (i. t.) administered antisera to different opioid peptides. Male NIH Swiss mice were pretreated i.t. with rabbit antisera to opioid peptides then exposed 24 h later to one of three different concentrations of nitrous oxide in oxygen. Dose-response curves constructed from the data indicated that the antinociceptive effect of nitrous oxide was significantly antagonized by antisera to various dynorphins (DYNs) and methionine-enkephalin (ME), but not by antiserum to beta-endorphin (beta-EP). The AD(50) values for nitrous oxide antinociception were significantly elevated by antisera to DYNs and ME but not beta-EP. These findings of this study support the hypothesis that nitrous oxide antinociception in the mouse abdominal constriction test involves the neuronal release of DYN and ME in the spinal cord.     

寒温带兴安落叶松林土壤温室气体通量的时间变异

采用静态箱/气相色谱(GC)法,对寒温带兴安落叶松林区6-9月生长季土壤CO2、CH4和N2O通量进行原位测定,研究了土壤温室气体通量的季节和昼夜变化及其与环境因子的关系.结果表明:在生长季,兴安落叶松林土壤为大气CH4的汇,吸收通量为22.3～107.8 μg CH4-C·m-2·h-1,6-9月月均甲烷吸收通量为(34.0±7.1)、(71.4±9.4)、(86.3±7.9)和(40.7-±6.2) μg·m-2·h-1;不同季节土壤CH4昼夜通量的变化规律相同,一天中均在10:00达到最大吸收高峰.土壤CO2日通量呈明显的双峰曲线,月均CO2通量大小顺序为7月＞8月＞6月＞9月.土壤N2O通量变异较大,在-9.1 ～31.7μg·m-2·h-1之间.土壤温度和湿度是影响CO2和CH4通量的重要因子,N2O通量主要受温度的影响.在兴安落叶松林区,10:00左右观测获得的温室气体地-气交换通量,经矫正后可以代表当日气体通量.     

Mechanism of nitrite reduction to nitrous oxide in a photodenitrifier,Rhodopseudomonas sphaeroide forma sp. denitrificans

The mechanism of anaerobic reduction of NO₂^? to N₂O in a photodenitrifier, Rhodopseudomonas sphaeroides forma sp. denitrificans, was investigated. With ascorbate-reduced phenazine methosulfate (PMS) as the electron donor, the nitrite reductase of this photodenitrifier reduced NO₂^? to NO and a trace amount of N₂O. With dithionite-reduced benzyl viologen as the electron donor, the major product of NO₂^? reduction was NH₂OH, and a trace amount of N₂O was also produced. The nitrate reductase itself had no NO reductase activity with ascorbate-reduced PMS. It was concluded that the essential product of NO₂^? reduction by the purified nitrite reductase is NO. Chromatophore membranes stoichiometrically produced N₂O from NO₂^? with any electron donor, such as dithionite-redduced benzyl viologen, ascorbate-reduced PMS or NADH/FMN. The membranes also contrained activity of NO reduction of N₂O with either ascorbate-reduced PMS or duroquinol. The NO reductase activity with duroquinol was inhibited by antimycin A. Stoichiometric production of N₂O from N₂^? also was observed in the reconstituted NO₂^? reduction system which contained the cytochrome bc₁ complex, cytochrome c₂, the nitrite reductase and duroquinol as the electron donor. The preparation of the cytochrome bc₁ complex itself contianed NO reductase activity. From these results the mechanism of NO₂^? reduction to N₂O in this photodenitrifier was determined as the nitrite reductase reducing NO₂^? to NO with electrons from the cytochrome bc₁ complex, and NO subsequently being reduced, without release, to N₂O with electrons from the cytochrome bc₁ complex by the NO reductase, which is closely associated with the complex.     

Copper-sulfur complexes supported by N-donor ligands: Towards models of the CuZ site in nitrous oxide reductase

The distinctive structure of the [(his)₇Cu₄(μ-S)]ⁿ⁺ cluster in the “Cu_Z” active site of nitrous oxide reductase and the intriguing mechanistic hypotheses for its catalytic reactivity provide inspiration for synthetic model studies aimed at characterizing relevant copper-sulfur compounds and obtaining fundamental insights into structure and bonding. In this brief review, we summarize such studies that have focused on the synthesis and characterization of a range of copper-sulfur complexes supported by N-donor ligands. Compounds with variable nuclearities and sulfur redox levels have been isolated, with the nature of the species obtained being dependent on the supporting ligand, sulfur source, and the reaction conditions. Spectroscopic data and theoretical calculations, often performed with a view toward drawing comparisons to oxygen analogs, have provided insight into the nature of the copper-sulfur bonding interactions in the complexes.     

基于变分方法的内蒙古典型草原水热通量估算

利用内蒙古典型草原生长季(2004年8月13～18日、2005年5月21～26日)和非生长季(2004年12月10～15日)共18 d的涡动相关系统观测资料(10 Hz输出1次)和小气候梯度系统在线输出资料(0.5 h输出1次),分析了变分方法对草原陆气通量估算的准确性.结果表明,变分法估算的感热与潜热通量与涡动相关法观测结果的变化趋势较为一致,且能量闭合程度更高.变分法计算的感热通量在白天明显地较涡动相关法得到的通量值高,12:00前后两者通量都达到峰值,两者之差也达到峰值,而夜间则较为接近;变分法计算的潜热通量曲线的相位略微落后于涡动相关法的通量曲线,且夜间的涡动相关法测得的潜热通量负值极少,负值通量的绝对值也很小.这表明夜间大气稳定导致涡动相关法存在一定程度的通量低估现象.变分法与波文比能量平衡法对陆气通量的估算比较表明,变分法可避免能量平衡法计算不稳定导致的虚假峰值现象,计算结果较为稳定.     

Effect of carbon source and competition for electrons on nitrous oxide reduction in a mixed denitrifying microbial community

The competition for electrons has been recently demonstrated to affect the reduction rates of the nitrogen oxides in a methanol enriched denitrifying community. The aim of this study was to test if electron competition also occurred when other substrates were used for denitrification and if that could have an effect on the potential nitrous oxide (N₂O) production and subsequent consumption. A denitrifying culture was developed in a sequencing batch reactor using nitrate as electron acceptor and a combination of acetate, ethanol and methanol as carbon sources. Four sets of batch tests were conducted using acetate, ethanol, methanol and a combination of the three carbon sources respectively. For each set the effect of nitrate, nitrite and nitrous oxide on each other reduction rates when present individually or in combination was assessed. Results show that reduction rates are affected by the type of substrate added, probably due to different microbial populations specialized with consuming a particular substrate. Also, N₂O reduction rate is the most reduced under the different electron competition scenarios tested, which results in N₂O accumulation in some cases. The effect of substrate limitation on N₂O reduction was also assessed.     

Prevalence of nitrous oxide reducing capacity in denitrifiers from a variety of habitats

Summary A total of 81 strains isolated by T. N. Gamble from soils from eight countries, fresh water lake sediments and nitrified poultry manure were examined for their ability to grow on N₂O as their electron acceptor, as well as for their tendency to produce N₂O from NO ₃ ⁻ in the absence and presence of acetylene. Seventy-seven of the 81 strains were confirmed as denitrifiers. Fifty-nine of the 77 strains grew on N₂O, while 12 strains produced N₂O but could not utilize it. Six strains reduced NO ₃ ⁻ to N₂ but could not grow on N₂O, suggesting that even if N₂O is always an intermediate product of denitrification, it is not always a freely diffusible intermediate. The organisms, however, would consume N₂O that accumulated early in growth and accumulated N₂O in the presence of acetylene. Thus the total number of N₂O users was 65 strains or 83% of the total tested. This implies that the N₂O reducing capacity of denitrifiers occur widely in nature. A high proportion ofPseudomonas fluorescens biotype II reduced N₂O. The accumulation of N₂O from NO ₃ ⁻ in the presence of acetylene provides strong evidence that N₂O is generally an intermediate in denitrification as well as provides additional support for the usefulness of this chemical as a general inhibitor of N₂O reduction.     

内蒙古温带荒漠草原生态系统水热通量动态

基于2008年全年内蒙古温带荒漠草原的水热通量观测数据,对荒漠草原水、热通量的日、季动态进行了分析.结果表明：温带荒漠草原感热通量和潜热通量的日动态均呈单峰型曲线,在12:00-13:30左右达最大值,其与地表净辐射的日变化趋势基本一致,但感热和潜热的峰值出现时间较地表净辐射峰值出现时间滞后约1 h;温带荒漠草原感热通量和潜热通量的日累积最大值分别为319.01和425.37 W·m^-2,分别出现在5月30日和6月2日;月均感热通量与潜热通量的最大值分别出现在5月和6月,最小值分别出现在1月和12月.研究区土壤含水量与降水的相关性较好,表层土壤含水量对降水的反应最敏感,深层土壤水分对降水的反应存在位相滞后.感热通量和潜热通量的季节动态与地表净辐射基本一致,均受降水影响.感热通量受地表净辐射的影响明显,而潜热通量对降水的反应较敏感,且土壤含水量在潜热通量中起主要作用.     

内蒙古典型草原作物系数的动态模拟与确定

作物系数是计算作物需水量必不可少的参数。利用2008年野外水分试验和4个气象站近26年的土壤水分和气象等常规观测资料, 以相关分析和回归分析等统计学方法为基础, 根据水量平衡原理计算了内蒙古典型草原区的作物系数, 分析了其在生长期和不同站点间的变化规律; 建立了典型草原标准作物系数与返青后年日数和大于0 ℃积温的模拟方程, 相关指数在0.94以上。在分析湿润指数、叶面积指数和盖度与作物系数关系的基础上, 提出标准作物系数的气候修正方法和胁迫条件下作物系数的修正方法。同时, 与修正后的联合国粮农组织(FAO)推荐值比较后得出, 生长季标准作物系数的平均值为0.60, 最大值为1.02; 不同生长阶段作物系数的典型值分别为: 初始生长期0.40, 生长中期0.93, 生长后期0.80, 相应的阈值范围为0.35-0.45、0.85-1.00和0.70-0.90。通过旬蒸散量的模拟计算值与蒸渗仪实测结果的比较, 平均相对误差在20%-24%之间, 生长旺盛期大多低于10%, 从而初步证明该文提出的方法在内蒙古典型草原区有较好的适用性。     

锡林郭勒生物圈保护区草原生态系统服务间接价值动态评估

草地是我国面积最大的陆地生态系统类型,对于维持我国北方的生态安全具有重要价值。北方草原的大面积退化已引起人们的极大关注。以内蒙古锡林郭勒生物圈保护区为研究区域．利用2个年份的遥感数据,结合地面样方调查,在GIS的支持下,绘制出草原退化空间分布图。选取草原生态系统在控制土壤侵蚀、减少土壤肥力流失、营养物质循环、CO2储存和O2释放方面的功能指标,对草原生态系统服务间接价值进行了动态评估。1985年和1999年草原退化面积分别为7190．9和7689．3km^2,占研究区总面积的67．19％和71．86％。2个年份草原生态系统间接服务总价值分别为28．24和26．75亿元．下降了5．28％,单位面积间接服务价值分别为2990和2830元。下降了5．35％。人类的过度放牧是导致草原大面积退化,生态系统功能降低和服务价值下降的主要原因。     

Effects of sulfide and low redox potential on the inhibition of nitrous oxide reduction by acetylene in Pseudomonas nautica

Membrane introduction mass spectrometry was used to investigate the inhibitory effect of acetylene on the nitrous oxide reductase activity of intact cells of Pseudomonas nautica. We studied the effects of the concentrations of nitrate and sulfide, and the redox potential, which have all been implicated in causing a decrease in the inhibitory effects of acetylene during measurements of denitrification in natural environments. There was no evidence that the concentration of nitrate influenced the effect of acetylene. Lowering the redox potential with the reductant Ti(III)-nitrilotriacetate caused a slight alleviation of acetylene inhibition. Much greater effects at the same redox potential were obtained with concentrations of sulfide in the range 1-10 microM.     

放牧和刈割对内蒙古典型草原大型土壤动物的影响

采用连续3年全季节放牧、3种季节性轮牧、秋季刈割和不利用对照6种处理, 研究了内蒙古典型草原大型土壤动物群落特征.调查在春、夏和秋3个季节进行,共捕获大型土壤动物597只,隶属于2门4纲11目,49个类群.结果表明: 全季节放牧导致土壤动物的个体密度、生物量和多样性降低;而刈割的影响相对较轻,土壤动物的个体密度、生物量和多样性甚至有提高趋势.3种季节性轮牧处理中,夏季和秋季放牧2次处理对土壤动物群落个体密度、生物量和多样性等指标的负面影响较轻.刈割管理对退化典型草原大型土壤动物群落的恢复较为有利;夏季和秋季放牧2次处理对大型土壤动物群落的负面影响较轻,是较理想的草地可持续管理措施.     

新疆天山高寒草原不同放牧管理下的CO_2,CH_4和N_2O通量特征

以中国科学院新疆巴音布鲁克草原生态站为依托,于2010年5月—2011年10月利用静态箱-气相色谱法对短期禁牧(2005年围封)、长期禁牧(1984年围封)和自由放牧(冬季放牧)3种草地的CO2、CH4、N2O气体通量进行了野外连续试验研究。结果表明:新疆天山高寒草原对CO2,CH4和N2O通量表现出明显的季节排放特点。在植物的生长季(5—10月),新疆天山高寒短期禁牧、长期禁牧和自由放牧草原的CO2通量平均值分别为:(89.8±49.3)、(52.8±28.7)、(57.0±30.7)mg·m-2·h-1,CH4通量平均值分别为:(-66.3±21.3)、(-104.5±32.8)、(-103.0±39.0)μg·m-2·h-1,N2O通量平均值分别为:(21.2±11.8)、(13.6±6.9)、(13.2±6.2)μg·m-2·h-1;短期禁牧草原与长期禁牧和自由放牧草原CH4平均通量具有显著性差异(P0.05),但CO2和N2O差异不显著(P0.05)。在植物的非生长季(11月—翌年4月),新疆天山高寒短期禁牧、长期禁牧以及自由放牧草原的3种温室气体的通量较低且差异均不显著。