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。     

冬玉米对氮肥的吸收利用和需求

在不同施氮量下 ,研究了冬玉米对氮肥的吸收利用 ,结果表明 :(1 )冬玉米地上各部分中氮的累积随着用氮量的增加而增加 ,花丝期前的吸收量均多于后期 ,但高氮区的前期吸氮比大于低氮区 ;(2 )营养体氮的转移率随施氮量的增加而降低 ,但绝对量依然是高氮处理大于低氮处理 ,其中雄穗的转移率最高 ,叶的转移量最大 ;(3 )氮肥利用率随施氮量的增加而提高 ,但氮的生产力下降。根据试验结果 ,在肥力好的土地上种植冬玉米以 1 80～ 2 70 kg N/hm2比较适宜     

陕西关中小麦-玉米轮作区协调作物产量和环境效应的农田适宜氮肥用量

为了确定陕西关中小麦-玉米轮作区兼顾作物产量和环境效应的农田适宜氮肥用量,通过玉米-小麦-玉米连续3季田间试验研究了作物产量、氮肥利用效率、氮肥表观损失和土壤氮素平衡等对施氮量的响应。结果表明,随着氮肥用量的增加,不同年份作物产量和3季作物累计产量均表现为先增加后降低的趋势,而累计氮肥农学效率、氮肥表观利用率、氮肥吸收效率和氮肥偏生产力均表现为显著的降低趋势。土壤氮素平衡结果表明,随着施氮量的增加,低量施氮时(小麦施N150 kg/hm2,玉米施N180 kg/hm2),氮肥残留显著增加,表观损失和损失率变化不明显,而高量施氮时(小麦施N150 kg/hm2,玉米施N180 kg/hm2),氮肥残留变化不明显,表观损失和损失率却显著增加。回归和相关分析显示,矿质氮在土壤较深层次(100—200cm土层)大量累积是氮肥表观损失的重要途径之一。小麦施N 150 kg/hm2、玉米施N 180 kg/hm2时,作物即可获得相对较高的产量和氮肥利用率,且能保持作物收获前后土壤无机氮库的基本稳定,同时也可将氮肥表观损失降至较低水平。     

氮素添加对黄土高原典型草原长芒草氮磷重吸收率及C:N:P化学计量特征的影响

 为了解氮素沉降对草地群落的影响, 通过人工氮肥添加模拟试验, 研究了黄土高原天然草地优势植物长芒草(Stipa bungeana)在不同施氮水平下叶片和立枯物碳(C)、氮(N)、磷(P)元素含量的变化特征, 探讨了N素增加对N、P重吸收率和C : N : P化学计量比的影响及其内在联系。结果表明: 氮素添加显著增加了长芒草叶片的C、N和立枯物的N、P含量, 对叶片P和立枯物C含量无显著影响; 氮素添加显著降低了长芒草的N、P重吸收率, 对照处理的N、P重吸收率最高, 分别为60.35%和
71.75%, 并且, 在相同氮素处理条件下P的重吸收率显著大于N重吸收率; 随着氮素添加量的增大, 叶片的C : N降低, N : P和C : P增加, N : P为18.25–29.01。研究表明, 黄土高原天然草地群落主要受P限制, 随氮素沉降增加, P限制进一步加剧; 长芒草较高的N、P重吸收率是保证其在贫瘠的土壤中生存的重要机制。     

懒猴属的核糖体DNA变异及其种间分化关系

用１５种限制性内切酶和人２８Ｓ、１８ＳｒＤＮＡ探针构建了懒猴属各物种核糖体ＤＮＡ重复单位的限制性内切酶图谱。在进化速率较高的非转录间隔区,在大、中、小懒猴中分别定位了２３、２４、２４个酶切位点。大懒猴与中懒猴有１２个位点不同,与小懒猴有１４个位点不同,而中、小懒猴间则只有一个位点的差异。经过计算,大懒猴与中懒猴的遗传距离值为１２．６５％,与小懒猴的差异为１４．２４％,中、小懒猴间的差异则仅为０．７     

猪粪堆肥化处理过程中的氮素转变及腐熟度研究

经过63d堆肥化处理后,猪粪与木屑混合堆肥及猪粪,木屑与树叶混合堆肥的T－N分别从开始的1．57％和1．78％增加到2．0％和2．11％;水溶性NO3－N／水溶性T－N均从接近于0的水平增加到3％左右;水溶性有机N／水溶性T－N分别增加到70％和76％;水溶性NH4－N／水溶性T－N则分别从开始52％和61％下降至堆肥结束时的30％和24％。种子发芽系数的测定结果表明,加入树叶有利于猪粪的腐熟化,可使猪粪堆肥化处理所城的时间从42d缩短至35d。化学指标与种子发芽系数的相关分析结果表明,水溶性NH4－N／水溶性T－N,水溶性NO3－N／水溶性T－N和水溶性有机N／水溶性T－N均与种子发芽系数呈显著相关,可作为堆肥的腐熟度评价指标。     

秸秆在土壤内分解初期氮素矿化与固持的模拟测定

利用模拟软件Modelmaker对3种作物秸秆在土壤内分解初期氮素循环转化过程进行了模拟,取得了土壤铵态氮、硝态氮、微生物氮及其¹⁵N丰度等个变量模拟值和测定值的良好一致性.模型模拟对氮转化速率测定的结果表明,土壤微生物主要固持铵态氮,对硝态氮固持非常微弱.氮矿化主要发生于作物秸秆,腐殖质氮的矿化极其微弱.一级动力学方程对秸秆氮素矿化过程的描述优于零级动力学方程.微生物固持氮的再矿化过程落后于氮固持过程,假定再矿化不发生或认为再矿化与固持化同时进行可导致氮矿化与固持速率测定的严重误差.忽略氮硝化过程和挥发损失将导致氮矿化和固持速率的测定值偏低.净固持或净矿化的产生不仅与秸秆碳氮比有关,而且与秸秆在土壤内分解时间有关.     

减量施氮对冬小麦-夏玉米种植体系中氮利用与平衡的影响

研究了冬小麦-夏玉米种植体系中减量施N对作物N利用与平衡的影响,结果表明,与原有高量施N处理(N240和N360)相比,在冬小麦季减半施N未引起产量和吸N量的变化。但在原有低量施N处理(N120)下减半施N显著降低了小麦产量和吸N量;在夏玉米季,在上季减半施N的基础上停止施N后作物产量和吸N量均比原固定施N处理显著下降,N平衡计算结果表明,减量施N条件下0～1m土壤N残留和表观损失的数量均显著低于原有施N量处理,作物N利用率显著提高,但在1～2m层次中累积的硝态氮却不因减量施N而下降,说明这一土层的硝态氮可能难以被作物吸收利用,由此可见,在前茬高施N量下减少氮肥用量有利于提高作物的氮肥利用率、减少N残留与表观损失。     

Functional analysis of individual oligosaccharide chains of Sendai virus hemagglutinin-neuraminidase protein

The roles of N-linked glycosylation in the intracellular transport and biological activities of the Sendai virus hemagglutinin-neuraminidase (HN) protein were studied. The protein contains four potential N-glycosylation sites: N77, N448, N499, and N511. By site-directed mutagenesis of these positions, the mature protein contained three N-linked oligosaccharides attached to N77, N499, and N511. The role of each added oligosaccharide in the structure and functions of the protein was identified by characterization of surface expression, hemadsorption, and neuraminidase activities of the corresponding mutant proteins. Elimination of the sites of N499 and N511 had the most detrimental effect, decreasing surface expression and hemadsorption. Elimination of the sites of N77 and N448 had similar but weaker effects. Mutants missing the sites of N499 and N511 were not able to induce syncytia formation in cells expressing mutant HN proteins and the fusion protein. Therefore, the N-linked oligosaccharides attached to N499 and N511 were important for intracellular transport and for the fusion promotion.     

模拟氮沉降对克氏针茅草原土壤有机碳的短期影响

为更好地了解天然草地土壤有机碳对氮沉降增加的响应,2011年在内蒙古太仆寺旗的克氏针茅(Stipa krylovii)草原上开展了模拟氮沉降的控制实验,设置对照(CK)和5个模拟氮沉降(NO-3)处理,分别为2(N1)、5(N2)、10(N3)、25(N4)和50 g N m-2a-1(N5)。生长季末,采集每个样地中0—2 cm和2—10 cm深度土壤进行有机碳含量及组成的分析,并进行实验室矿化培养。结果表明,土壤颗粒态有机碳(POC)对氮添加响应敏感,N1和N2处理下的POC含量高于CK,N3、N4和N5处理则低于CK。5个模拟氮沉降处理下的矿质结合态有机碳(MOC)含量均高于对照,但差别不显著。不同氮沉降水平下0—2 cm土层的碳矿化潜势为N2N1N4N3CKN5,且N1,N2,N3和N4处理均显著高于CK和N5;2—10 cm土层的碳矿化潜势为N2N1N3CKN4N5,N1、N2和N3显著高于CK、N4及N5。不同施氮处理对群落净第一性生产力有明显影响,N5的净第一性生产力和地上生物量显著低于对照和其它施氮处理,N1的0—10 cm地下生物量显著高于对照和其它处理,N5的凋落物量显著高于对照。模拟氮沉降短期内对土壤总有机碳(SOC)含量无显著影响。     

氮磷添加对荒漠草原植物-凋落物-土壤生态化学计量特征的影响

为明确植物、凋落物和土壤养分含量及化学计量比对土壤中添加多种限制性养分的响应,阐明“植物-凋落物-土壤”连续体化学计量动态及各组分之间的协同作用,以宁夏荒漠草原为研究对象,于2018年开始进行氮(N)、磷(P)养分添加控制试验。试验处理包括对照(CK)、N添加、P添加、NP共同添加4个处理。结果表明：(1)NP共同添加显著增加了荒漠草原植物N和P含量、以及凋落物和土壤P含量,显著降低了荒漠草原植物C∶N和C∶P、以及土壤和凋落物C∶P和N∶P。P添加显著增加了荒漠草原植物、凋落物和土壤P含量,显著降低了植物、凋落物、土壤C∶P和N∶P。N添加分别增加了植物、凋落物N含量和N∶P,但对植物N含量影响未达到显著水平。(2)C、N、P含量和N∶P大小均表现为植物>凋落物>土壤,C∶N和C∶P均表现为凋落物>植物。(3)N添加提高了荒漠草原植物对P再吸收效率,降低了荒漠草原植物对N利用效率;P添加提高荒漠草原植物对N再吸收效率,降低荒漠草原对P的利用效率;NP共同添加提高了荒漠草原植物对N和P再吸收效率,降低了荒漠草原植物对N和P利用效率。(4)植物-凋落物-土壤的N、P含量...     

高肥力土壤条件下不同基因型花生对氮素利用的差异

在桶栽条件下,利用¹⁵N示踪技术,选用20个基因型花生为供试材料,研究了高肥力土壤条件下不同基因型花生对氮素利用的差异.结果表明:高肥力土壤条件下花生氮素营养以土壤氮为主,根瘤固氮次之,肥料氮最低.不同基因型间花生对全氮、肥料氮、土壤氮和根瘤固氮的吸收和积累均存在显著差异,基因型间遗传变异以根瘤固氮最大,肥料氮和土壤氮相当.氮素荚果生产效率和氮肥利用率基因型间差异显著,最高值分别为最低值的3.6和2.1倍.全氮、肥料氮、土壤氮和根瘤固氮的氮素收获指数基因型间均存在显著遗传变异,且以根瘤固氮的氮素收获指数基因型间遗传变异最大.花生荚果产量与不同氮源氮素积累量及氮素收获指数、氮素荚果生产效率和氮肥利用率呈显著或极显著正相关.依据花生对不同氮源氮素吸收积累和荚果产量筛选出全氮高积累高产型、肥料氮高积累高产型、土壤氮高积累高产型和根瘤固氮高积累高产型四大类型花生,其中四大类型特征兼有的有4个花生基因型.     

Short-term immobilisation and crop uptake of fertiliser nitrogen applied to winter wheat: effect of date of application in spring

Previous studies on the fate of fertiliser nitrogen applied to winter wheat in temperate climates have shown that nitrogen (N) applied early, at tillering for wheat, was less efficiently taken up than N applied later in the growth cycle. We examined the extent to which the soil microbial N immobilisation varied during the wheat spring growth cycle and how microbial immobilisation and plant uptake competed for nitrogen. We set up a pulse-15N labelled field experiment in which N was applied at eight development stages from tillering (beginning of March) to anthesis (mid-June). Each application was 50 kg N ha-1 as 15N labelled urea except for the first application which was 25 kg N ha-1. The distribution of fertiliser 15N in shoots, roots, mineral and organic soil N was examined by destructive sampling 7 and 14 days after each 15N pulse. The inorganic 15N pool was almost depleted by day 14. The N uptake efficiency increased with later applications from 45% at tillering to 65% at flowering. N immobilisation was rather constant at 13–16% of N applied, whatever the date of application. The increase in plant 15N uptake resulted in an increase in the total 15N recovery in the plant-soil system (15N in soil +15N in plant), suggesting that gaseous losses were lower at the later application dates.     

冬枣对不同形态氮素的吸收与利用

以2年生盆栽鲁北冬枣为试材,研究了其对尿素、甘氨酸（Gly）和谷氨酸（Glu）的吸收利用与响应特性．结果表明：3种形态氮均可被冬枣吸收利用,与尿素相比,氨基酸态氮吸收的量较少．若尿素的吸收量以100％计,则叶片对Gly和Glu的相对吸收量分别为28．88％和11．73％,吸收到的氮素主要分配到叶片和枣头枝中;而根对Gly和Glu的相对吸收量则分别为50．48％和42．72％．冬枣吸收尿素、Gly和Glu后,叶片中的谷草转氨酶（GOT）和谷丙转氨酶（GPT）活性提高,可溶性蛋白质含量增加;但不同形态氮素处理对硝酸还原酶（NR）活性的影响存在差异,尿素可显著提高NR活性,Glu对NR活性影响不大,Gly降低了NR活性．与尿素相比,氨基酸态氮能明显提高冬枣果实的着色个数、着色面积以及果实中可溶性固形物含量．     

Accumulation characteristics of biomass and nitrogen and critical nitrogen concentration dilution model of cotton reproductive organ

Several nitrogen (N) field experiments were carried out in Nanjing and Anyang, China, to study the dynamic characteristics of biomass accumulation and N uptake, and to define the dilution curve for critical N concentration in cotton reproductive organ over the growth period. The results show that the total biomass and N accumulation were affected significantly by the rate of N application, exhibiting a sigmoid curve over time. The beginning time of fast N accumulation was 1–5 d earlier than that of biomass accumulation. The cotton lint yield was correlated with N concentration in the reproductive organ and fluctuated with varying N concentration, indicating the existence of luxurious N consumption in the cotton reproductive organ. The N concentration increased with increasing N application rates, and decreased gradually during the growth period. The relationship between biomass and N concentration can be described with a power equation. The patterns of the N concentration dilution model were consistent at both experimental sites, but the model parameter values of a differed. The results presented in this paper indicate that a critical N concentration dilution curve for cotton reproductive organ is independent of ecological region and can be described with a power equation.     

喀斯特区不同退化程度植被群落植物-凋落物-土壤-微生物生态化学计量特征

为摸清喀斯特植被退化对群落各组分C、N、P生态化学计量特征及内稳态特征的影响,为喀斯特退化生态系统植被恢复与重建提供科学依据,以桂西北喀斯特地区5种退化程度植被群落为研究对象,测定了不同退化程度植被群落植物叶片、凋落物、土壤和微生物生物量的C、N、P含量,分析其化学计量比特征、相互关系及植物内稳性特征。结果表明：(1)随着退化程度加剧,叶片C、N、P含量、N∶P和凋落物N∶P、微生物量C显著下降,而叶片C∶N、C∶P则显著增加,且植物叶片N∶P<14;随退化程度加剧,凋落物N、P含量、土壤C、N、P含量、微生物量N、P呈先略有增后显著降低的趋势,且不同退化程度群落土壤N∶P和微生物量C∶N无显著差异。(2)叶片N、P含量与土壤N、P含量,叶片C∶P与土壤C∶N、C∶P、N∶P,叶片N∶P与凋落物N、N∶P,叶片C、N、P含量与微生物量C呈显著或极显著正相关关系;叶片C∶N与土壤C、N,叶片C∶P与土壤N、P,叶片N∶P与土壤P呈显著或极显著负相关关系。(3)喀斯特地区植物叶片N、P元素的内稳性指数(H)平均值分别为2.74和2.31,属于弱稳态型,叶片N∶P的H值为5.14,为稳...     

Nitrogen 15 tracer studies on the pathway of denitrification in Pseudomonas aeruginosa.

The pathway of anaerobic reduction of nitrite to nitrogen gas (N2) by cell suspensions of the denitrifier, Pseudomonas aeruginosa, was studied using the techniques of gas chromatography and mass spectrometry. While release of nitrous oxide (N2O) is not normally detected during the reduction of nitrite to N2 by this organism, 15N from [15N]nitrite nevertheless can be trapped quantitatively as 15N2O in a pool of added N2O. In such experiments the abundance of 15N in N2O always exceeds that in product N2, consistent with the absence of a major reductive route from nitrite to N2 which by-passes N2O. During the reduction of a mixture of [15N]nitrite and nitric oxide (NO), 15NO produced at most only in trace amounts. The final products are chiefly 15N2 and 14N2 with only a small fraction of the scrambled product, 14N15N. Much of the 14N15N can be accounted for as an artifact caused by traces of molecular oxygen, which promote the conversion of NO to nitrite by autooxidation and thereby degrade slightly the isotopic purity of [15N]nitrite. Nitrous oxide shows all the properties of a free obligatory intermediate during the denitrification of nitrite to N2 by P. aeruginosa, whereas NO does not. The inability to trap 15NO in a pool of NO indicates that NO is not a free obligatory intermediate in the reduction of nitrite. The small mole fractions of 14N15N produced from a mixture of [15N]nitrite and NO require that the main reductive pathways for these nitrogen oxides cannot share any freely diffusible mono-nitrogen intermediate in common. The simplest interpretation is that nitrite and NO are denitrified by separate pathways, at least prior to the formation of the first bi-nitrogen compound.     

Side-chain structures in the first turn of the alpha-helix

The first three residues at the N terminus of the alpha-helix are called N1, N2 and N3. We surveyed 2102 alpha-helix N termini in 298 high-resolution, non-homologous protein crystal structures for N1, N2 and N3 amino acid and side-chain rotamer propensities and hydrogen-bonding patterns. We find strong structural preferences that are unique to these sites. The rotamer distributions as a function of amino acid identity and position in the helix are often explained in terms of hydrogen-bonding interactions to the free N1, N2 and N3 backbone NH groups. Notably, the "good N2" amino acid residues Gln, Glu, Asp, Asn, Ser, Thr and His preferentially form i, i or i,i+1 hydrogen bonds to the backbone, though this is hindered by good N-caps (Asp, Asn, Ser, Thr and Cys) that compete for these hydrogen bond donors. We find a number of specific side-chain to side-chain interactions between N1 and N2 or between the N-cap and N2 or N3, such as Arg(N-cap) to Asp(N2). The strong energetic and structural preferences found for N1, N2 and N3, which differ greatly from positions within helix interiors, suggest that these sites should be treated explicitly in any consideration of helical structure in peptides or proteins.     

棉花蕾花铃生物量、氮累积特征及临界氮浓度稀释模型

在大田栽培条件下,于河南安阳（黄河流域黄淮棉区）和江苏南京（长江流域下游棉区）设置了棉花氮素水平试验,对不同氮素水平条件下棉花蕾花铃的生物量、氮素累积及氮浓度的动态变化进行分析,并依据Justes的临界氮浓度稀释模型确定方法,研究棉花蕾花铃临界氮浓度稀释模型。结果表明：棉花蕾花铃的生物量增长和氮吸收累积均受氮素水平的影响,其动态变化符合S型曲线,氮累积的快速起始时间较生物量早1～5d;氮浓度过高或过低均不利于产量形成,蕾花铃等器官存在氮奢侈消费现象;氮浓度随施氮量的增加而升高、随生育进程的推移而降低,其生物量累积量与氮浓度间符合幂函数关系,两试点蕾花铃氮稀释曲线模型形式相同,但模型参数a不同,不同生态区存在独立的临界氮稀释曲线模型。由于临界稀释模型具有明确的生物学意义,可以作为定量诊断蕾花铃氮营养动态变化的指标之一。     

Nitrogen management in a maize-groundnut crop rotation of humid tropics: effect on N2O emission

Development of appropriate land management techniques to attain sustainability and increase the N use efficiency of crops in the tropics has been gaining momentum. The nitrous oxides (N2Os) affect global climate change and its contribution from N and C management systems is of great significance. Thus, N transformations and N2O emission during maize-groundnut crop rotation managed with various N sources were studied. Accumulation of nitrate (NO3- ) and its disappearance happened immediately after addition of various N sources, showing liming effect. The mineral N retained for 2-4 weeks depending on the type and amount of N application. The chicken manure showed rapid nitrification in the first week after application during the fallow period, leading to a maximum N2O flux of 9889 g N2O-N m(-2) day(-1). The same plots showed a residual effect by emitting the highest N2O (4053 microg N2O-N m(-2) day(-1)) during maize cultivation supplied with a half-rate of N fertilizer. Application of N fertilizer only or in combination with crop residues exhibited either lowered fluxes or caused a sink during the groundnut and fallow periods due to small availability of substrates and/or low water-filled pore space (<40%). The annual N2O emission ranged from 1.41 to 3.94 kg N2O-N ha(-1); the highest was estimated from the chicken manure plus crop residues and half-rate of inorganic N-amended plots. Results indicates a greater influence of chicken manure on the N transformations and thereby N2O emission.