Relative concentrations of N15 in urinary ammonia N and urea N after feeding N15-labeled compounds

Available data on the isotopic ratio See PDF for Equation of ammonia (r_a) and that of urea (r_u) after a single feeding of glycine, aspartic acid, and ammonium citrate are analyzed. From this analysis the following conclusions are drawn. 1. The isotopic ratio See PDF for Equation of ammonia (r_a) is always higher than that of urea (r_u) in the initial period after a single feeding of isotopic glycine or aspartic acid, but the relation is reversed later. A similar relation probably holds after feeding isotopic ammonia. 2. It is pointed out that the ratio of average r_a to average r_u depends on the time interval for which urine is collected, on the schedule of feeding, and probably also on the amount taken at each feeding. When the amount fed and the feeding schedule are unknown, theoretical interpretation of the ratio of average r_u to average r_u is impossible. 3. At the point of maximum isotopic ratio of urea, it is very probably equal to the isotopic ratio of ammonia. A possible explanation is suggested.     

N deposition, N transformation and N leaching in acid forest soils

Nitrogen deposition, mineralisation, uptake and leaching were measured on a monthly basis in the field during 2 years in six forested stands on acidic soils under mountainous climate. Studies were conducted in three Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] plantations (D20: 20 year; D40: 40 yr; D60: 60 yr) on abandoned croplands in the Beaujolais Mounts; and two spruce (Picea abies Karst.) plantations (S45: 45 yr; S90: 90 yr) and an old beech (Fagus sylvatica L.) stand (B150: 150 yr) on ancient forest soils in a small catchment in the Vosges Mountains. N deposition in throughfall varied between 7–8 kg ha^–1 year^–1 (D20, B150, S45) and 15–21 kg ha^–1 yr^–1 (S90, D40, D60). N in annual litterfall varied between 20–29 kg ha^–1 (D40, D60, S90), and 36–43 kg ha^–1 (D20, S45, B150). N leaching below root depth varied among stands within a much larger range, between 1–9 kg ha^–1 yr^–1 (B150, S45, D60) and 28–66 kg ha^–1 yr^–1 (D40, S90, D20), with no simple relationship with N deposition, or N deposition minus N storage in stand biomass. N mineralisation was between 57–121 kg ha^–1 yr^–1 (S45, D40, S90) and between 176–209 kg ha^–1 yr^–1 in (B150, D60 and D20). The amounts of nitrogen annually mineralised and nitrified were positively related. Neither general soil parameters, such as pH, soil type, base saturation and C:N ratio, nor deposition in throughfall or litterfall were simply related to the intensity of mineralisation and/or nitrification. When root uptake was not allowed, nitrate leaching increased by 11 kg ha^–1 yr^–1 at S45, 36 kg ha^–1 yr^–1 at S90 and between 69 and 91 kg ha^–1 yr^–1 at D20, D40, B150 and D60, in relation to the nitrification rates of each plot. From this data set and recent data from the literature, we suggest that: high nitrification and nitrate leaching in Douglas-fir soils was likely related to the former agricultural land use. High nitrification rate but very low nitrate leaching in the old beech soil was related to intense recycling of mineralised N by beech roots. Medium nitrification and nitrate leaching in the old spruce stand was related to the average level of N deposition and to the deposition and declining health of the stand. Very low nitrification and N leaching in the young spruce stand were considered representative of fast growing spruce plantations receiving low N deposition on acidic soils of ancient coniferous forests. Consequently, we suggest that past land use and fine root cycling (which is dependent on to tree species and health) should be taken into account to explain the variability in the relation between N deposition and leaching in forests.     

Neotyphodium coenophialum和N.lolii的PCR检测

以N·coenophialum和N·lolii及其近似种N·huerfanum、N·chisosum、N·aotearoae、N·sp·共6个种18个菌株及苇状羊茅和多年生黑麦草8个品种的供试种子,通过对Tub-2基因引物IS1~IS3和NC25基因引物F1~R1进行扩增,设计了种子中Neotyphodium属内生真菌套式扩增的通用引物Tub-2-F~Tub-2-R,设计了N·coenophialum和N·lolii的特异引物F3~R3,建立了N·coenophialum和N·lolii的菌丝常规PCR和单粒种子套式PCR检测方法,使N·coenophialum和N·lolii的检测达到了单粒种子的水平,缩短了检测时间。建立的N·coenophialum和N·loliiPCR检测方法特异性强,结果可靠,检测速度快。     

Studies on the availability of Azolla N and urea N for rice growth using 15N

Field experiments (20 m² plots) were conducted to compare Azolla and urea as N sources for rice (Oryza sativa L.) in both the wet and dry seasons. Parallel microplot (1 m²) experiments were conducted using ¹⁵N. A total of approximately 60 kg N ha^-1 was applied as urea, Azolla, or urea plus Azolla. Urea or Azolla applied with equal applications of 30 kg N ha^-1 at transplanting (T) and at maximum tillering (MT) were equally effective for increasing rice grain yields in both seasons. Urea at 30 kg N ha^-1 at T and Azolla 30 kg N ha^-1 at MT was also equally effective. Urea applied by the locally recommended best split (40 kg at T and 20 kg at MT) gave a higher yield in the wet season, but an equal yield in the dry season. The average yield increase was 23% in the wet season, and 95% in the dry season. The proportion of the N taken up by the rice plants which was derived from urea (%NdfU) or Azolla (%NdfAz) was essentially identical for the treatments receiving the same N split. Recovery of ¹⁵N in the grain plus straw was also very similar. Positive yield responses to residual N were observed in the succeeding rice crop following both the wet and dry seasons, but the increases were not always statistically significant. Recovery of residual ¹⁵N ranged from 5.5 to 8.9% for both crops in succeeding seasons. Residual recovery from the urea applications was significantly higher than from Azolla in the crop succeeding the dry season crop. Azolla was equally effective as urea as an N source for rice production on a per kg N basis.     

Effects of N fertilization on N2 fixation and N balances of soybean grown after lowland rice

We report a study in northern Thailand to examine the effects of fertilizer N, applied both to paddy rice and to a subsequent soybean crop on symbiotic and yield characteristics of soybean and on the differences between inputs of fixed N₂ and the removal of N as harvested product. Treatments were a factorial arrangement of 0, 100 and 300 kg N ha^-1 applied to the rice (designated R0, R100 and R300, respectively), and 0,25 and 50 kg N ha^-1, applied as starter fertilizer to the soybean (S0, S25 and S50, respectively).Nitrogen applied to the rice increased rice yields by up to 74% but proportions recovered by the rice were low (45% [R100] and 14% [R300]). The rice N treatments had only marginal effects on soybean nodulation (up to 17% reduction in early growth) and above-ground dry matter (up to 9% increase). Effects on soybean seed yield and total N₂ fixed were insignificant. Starter N, applied to the soybean at sowing, also marginally reduced nodulation and enhanced above-ground dry matter. Total N₂ fixed was unaffected but seed yield was increased by up to 6%. For all treatments, total above-ground N ranged from 145 to 179 kg ha^-1 with 72 to 85% (122 and 140 kg ha^-1) derived from N₂ fixation. When harvested product consisted of seed only, differences between inputs of fixed N₂ and removals of seed N were close to zero (-10 to+9 kg N ha^-1) with little effect of fertilizer N. The N balances were reduced by an average of 18 kg N ha^-1 when straw was included as harvested product. We concluded that N applied to the rice and to the following soybean was inefficiently used by those crops and had only marginal effects of symbiotic activity of the soybean. Furthermore, the benefit of the N₂ fixing soybean in this system was to slow the decline of, rather than enhance, the N fertility of the soil     

灌溉方式和施氮量对棉田氮肥利用率及损失的影响

在田间条件下,研究不同灌溉方式(滴灌和漫灌)和不同施氮水平(0、240、360、480kg N·hm-2)对棉田氮肥利用率及损失的影响,并定量分析了氮肥被植株吸收、土壤硝态氮残留,以及氨挥发、硝态氮淋溶损失、硝化反硝化损失等氮素循环转化途径.结果表明:滴灌棉花籽棉产量、植株吸氮量和氮肥利用率均显著大于漫灌.漫灌土壤硝态氮残留量显著高于滴灌;在不同施氮量处理中滴灌土壤氨挥发损失量占肥料氮施用量的比例为0.06％～0.14％,且显著高于漫灌;滴灌和漫灌硝态氮淋溶损失量占肥料氮施用量的比例分别为4.4％和8.8％,与漫灌相比,滴灌能显著降低淋溶水中硝态氮淋失量;滴灌和漫灌肥料氮的硝化-反硝化损失量分别占肥料氮施用量的17.9％和16.8％.硝态氮淋溶和硝化-反硝化损失是新疆棉田氮素损失的主要途径.     

氮和钙交互作用对番茄氮素吸收的影响

以沈阳草甸土为栽培基质,采用二次D-饱和最优设计,进行番茄N、Ca两因素效应的盆栽试验,结果表明,在本试验条件下,番茄茎、叶、果实中氮素含量随生育期的进展而下降,氮肥对番茄果实中NO3^--N含量影响呈直线正效应,但各处理番茄果实中NO3^--N含量均不超过可生食标准．适量施用钙肥有利于控制果实中NO3^--N含量,氮肥对番茄植株地上部分和果实中N含量影响均符合报酬递减律．氮肥和钙肥对番茄N素积累符合报酬递减律;番茄从开花期到果实膨大期属N素最大效应期．番茄叶片硝酸还原酶活性受氮素影响较大．N、Ca配合施用,有利于提高番茄叶片硝酸还原酶活性,钙素可降低硝酸还原酶活性,土壤中NO3^--N含量和电导率EC值均随氮肥施用增加而提高。     

脲酶／硝化抑制剂对土壤有效态氮、微生物量氮和小麦氮吸收的影响

研究了脲酶抑制剂(NBPT)、硝化抑制剂(DCD)及二者组合在草甸棕壤上施用对尿素态N转化及土壤总有效态N、微生物量N的影响．结果表明,尿素配施NBPT、DCD及抑制剂组合能够增加尿素水解后土壤NH4^+含量2％-53％。显著降低了氧化态N的浓度,抑制了土壤中铵态N的氧化,增加土壤总有效N34％-44％,小麦吸N量增加0．26％-6．79％。其中以脲酶抑制剂与硝化抑制剂组合的效果最明显．抑制剂施用增加了微生物在小麦生长初期对有效态N固持,有利于后期土壤有效态N的矿化．     

Bacterial immobilization and remineralization of N at different growth rates and N concentrations

An experiment was designed to resolve two largely unaddressed questions about the turnover of N in soils. One is the influence of microbial growth rate on mobilization and remineralization of cellular N. The other is to what extent heterotrophic immobilization of NO(3)(-) is controlled by the soil concentration of NH(4)(+). Bacteria were extracted from a deciduous forest soil and inoculated into an aqueous medium. Various N pool dilution/enrichment experiments were carried out to: (1) calculate the gross N immobilization and remineralization rates; (2) investigate their dependence on NH(4)(+)and NO(3)(-) concentrations; (3) establish the microbial preference for NH(4)(+)and NO(3)(-) depending on the NH(4)(+)/NO(3)(-) concentration ratio. Remineralization of microbial N occurred mainly at high growth rates and NH(4)(+) concentrations. There was a positive correlation between NH(4)(+) immobilization and remineralization rates, and intracellular recycling of N seemed to be an efficient way for bacteria to withstand low inorganic N concentrations. Thus, extensive remineralization of microbial N is likely to occur only when environmental conditions promote high growth rates. The results support previous observations of high NO(3)(-) immobilization rates, especially at low NH(4)(+) concentrations, but NO(3)(-) was also immobilized at high NH(4) concentrations. The latter can be understood if part of the microbial community has a preference for NO(3)(-) over NH(4)(+).     

Synthesis and conformational study of poly(N delta-carbobenzoxy, N delta-benzyl-L-ornithine) and poly(N delta-benzyl-L-ornithine)

Poly(N^δ-carbobenzoxy, N^δ-benzyl-L -ornithine) (PCBLO) was prepared by the standard NCA method. PCBLO was converted into poly(N^δ-benzyl-L -ornithine) (PBLO) through decarbobenzoxylation with hydrogen bromide. The monomer N^δ-benzyl-L -ornithine was synthesized by reacting L -ornithine with benzaldehyde, followed by hydrogenation. The conformation of the two polypeptides was studied by optical rotatory dispersion and circular dichroism. PCBLO forms a right-handed helix in helix-promoting solvents. In mixed solvents of chloroform and dichloroacetic acid (DCA) it undergoes a sharp helix–coil transition at 12% (v/v) DCA at 25°C, as compared with 36% for poly(N^δ-carbobenzoxy-L -ornithine) (PCLO). Like PCLO, the helix–coil transition is “inverse,” that is, high temperature favors the helical form. PBLO is soluble in water at pH below 7 and has a “coiled” conformation. In 88% (v/v) 1-propanol above pH (apparent) 9.6 it is completely helical. In 50% 1-propanol the transition pH (apparent) is about 7.4; this compares with a pH_tr of about 10 for poly-L -ornithine in the same solvent.     

土壤动物与N素循环及对N沉降的响应

以主要的生态过程之一——N循环为对象,论述了土壤动物不仅对凋落物的分解有重要影响,而且在N素矿化和植物对N的吸收过程中也起着重要作用。同时,日益严重的全球变化问题之一——N沉降对土壤动物的多样性及其在生态系统中的功能构成了极大的威胁。另还对土壤动物与N循环研究的方法、土壤动物在N循环过程中的作用机制、热带地区的需求及N沉降下土壤动物的响应作了探讨,并提出,开展大尺度的专类研究及长期定位研究成为下一步研究的需要。     

Determination of alpha-helix N1 energies after addition of N1, N2, and N3 preferences to helix/coil theory

Surveys of protein crystal structures have revealed that amino acids show unique structural preferences for the N1, N2, and N3 positions in the first turn of the alpha-helix. We have therefore extended helix-coil theory to include statistical weights for these locations. The helix content of a peptide in this model is a function of N-cap, C-cap, N1, N2, N3, C1, and helix interior (N4 to C2) preferences. The partition function for the system is calculated using a matrix incorporating the weights of the fourth residue in a hexamer of amino acids and is implemented using a FORTRAN program. We have applied the model to calculate the N1 preferences of Gln, Val, Ile, Ala, Met, Pro, Leu, Thr, Gly, Ser, and Asn, using our previous data on helix contents of peptides Ac-XAKAAAAKAAGY-CONH2. We find that Ala has the highest preference for the N1 position. Asn is the most unfavorable, destabilizing a helix at N1 by at least 1.4 kcal mol(-1) compared to Ala. The remaining amino acids all have similar preferences, 0.5 kcal mol(-1) less than Ala. Gln, Asn, and Ser, therefore, do not stabilize the helix when at N1.     

Natural 15N abundance of soil N pools and N2O reflect the nitrogen dynamics of forest soils

Natural ¹⁵N abundance measurements of ecosystem nitrogen (N) pools and ¹⁵N pool dilution assays of gross N transformation rates were applied to investigate the potential of δ¹⁵N signatures of soil N pools to reflect the dynamics in the forest soil N cycle. Intact soil cores were collected from pure spruce (Picea abies (L.) Karst.) and mixed spruce-beech (Fagus sylvatica L.) stands on stagnic gleysol in Austria. Soil δ¹⁵N values of both forest sites increased with depth to 50 cm, but then decreased below this zone. δ¹⁵N values of microbial biomass (mixed stand: 4.7 ± 0.8‰, spruce stand: 5.9 ± 0.9‰) and of dissolved organic N (DON; mixed stand: 5.3 ± 1.7‰, spruce stand: 2.6 ± 3.3‰) were not significantly different; these pools were most enriched in ¹⁵N of all soil N pools. Denitrification represented the main N₂O-producing process in the mixed forest stand as we detected a significant ¹⁵N enrichment of its substrate NO₃⁻ (3.6 ± 4.5‰) compared to NH₄⁺ (−4.6 ± 2.6‰) and its product N₂O (−11.8 ± 3.2‰). In a ¹⁵N-labelling experiment in the spruce stand, nitrification contributed more to N₂O production than denitrification. Moreover, in natural abundance measurements the NH₄⁺ pool was slightly ¹⁵N-enriched (−0.4 ± 2.0 ‰) compared to NO₃⁻ (−3.0 ± 0.6 ‰) and N₂O (−2.1 ± 1.1 ‰) in the spruce stand, indicating nitrification and denitrification operated in parallel to produce N₂O. The more positive δ¹⁵N values of N₂O in the spruce stand than in the mixed stand point to extensive microbial N₂O reduction in the spruce stand. Combining natural ¹⁵N abundance and ¹⁵N tracer experiments provided a more complete picture of soil N dynamics than possible with either measurement done separately.     

Elastic Properties of Zinc-blende G a N,A l N and I n N from Molecular Dynamics

Molecular dynamics calculations of the adiabatic elastic constants of group III-Nitrides for temperatures ranging from 300 to 900 K have been performed. The results show good agreement with first-principles calculations. The moduli decreased with increasing temperature. The structural properties of zinc-blende GaN, AlN and InN are reported. Good agreement between the calculated and experimental values of the lattice constant, the cohesion energy, and the bulk modulus and its derivative are obtained.     

15N natural abundances and N use by tundra plants

Plant species collected from tundra ecosystems located along a north-south transect from central Alaska to the north coast of Alaska showed large and consistent differences in ¹⁵N natural abundances. Foliar ¹⁵N values varied by about 10% among species within each of two moist tussock tundra sites. Differences in ¹⁵N contents among species or plant groups were consistent across moist tussock tundra at several other sites and across five other tundra types at a single site. Ericaceous species had the lowest ¹⁵N values, ranging between about –8 to –6. Foliar ¹⁵N contents increased progressively in birch, willows and sedges to maximum ¹⁵N values of about +2 in sedges. Soil ¹⁵N contents in tundra ecosystems at our two most intensively studied sites increased with depth and ¹⁵N values were usually higher for soils than for plants. Isotopic fractionations during soil N transformations and possibly during plant N uptake could lead to observed differences in ¹⁵N contents among plant species and between plants and soils. Patterns of variation in ¹⁵N content among species indicate that tundra plants acquire nitrogen in extremely nutrient-poor environments by competitive partitioning of the overall N pool. Differences in plant N sources, rooting depth, mycorrhizal associations, forms of N taken up, and other factors controlling plant N uptake are possible causes of variations in ¹⁵N values of tundra plant species.     

N,N,N-三甲基壳聚糖甲基硫酸盐的合成及理化性质的测定

壳聚糖与甲醛、甲酸反应得到N,N-二甲基壳聚糖,然后以硫酸二甲酯为季铵化试剂反应得到N,N,N-三甲基壳聚糖甲基硫酸盐(TMCMS),用IR1、H NMR和元素分析对其结构进行了表征。元素分析结果表明其季铵化度为74.6%,差示扫描量热法和热重分析法结果表明其热稳定性比壳聚糖差,但其水溶性明显优于壳聚糖,25℃时在水中的溶解度可达20 mg/mL,浓度为2 mg/mL时在pH 3～12范围内无沉淀产生。     

Dynamics of biomass and N accumulation of alfalfa under three N fertilization rates

The dynamics of biomass and N accumulation following defoliation of alfalfa and the application of N fertilization has rarely been studied under field conditions, particularly in the seeding year. Our objectives were to determine the effect of N fertilization on the dynamics of biomass and N accumulation during the first regrowth of alfalfa in the seeding year, and to determine if a model describing critical N concentration developed for established stands could be used in the seeding year. In two separate experiments conducted in 1992 and 1993, the biomass and N accumulation of alfalfa grown with three N rates (0, 40 and 80 kg N ha^-1) were determined weekly. Maximum shoot growth was reached with 40 kg N ha^-1 in 1992, and maximum shoot growth was not reached with the highest N fertilization rate in 1993. Nitrogen fixation, root N reserves and soil inorganic N uptake when no N was applied were, therefore, not sufficient to ensure non-limiting N conditions, particularly when growth rates were the highest between 14 to 21 d after defoliation. Nitrogen fertilization increased shoot biomass accumulation in the first 21 d of regrowth, biomass partitioning to the shoots and shoot and taproot N concentrations. The model parameters of critical N concentration developed by Lemaire et al. (1985) for established stands of alfalfa were not adequate in the seeding year. The N requirements per unit of shoot biomass produced are greater in the seeding year than on established stands, and this was attributed to a greater proportion of leaves in the seeding year.     

The Synthesis of RNA Containing the Modified Nucleotides N 2-Methylguanosine and N 6, N 6-Dimethyladenosine

Abstract

The phosphoramidites of the naturally occurring modified nucleotides N ²-methylguanosine and N ⁶,N ⁶-dimethyladenosine were synthesized and incorporated into short oligoribonucleotides. Described are the syntheses of the phosphoramidites and the procedures used to deprotect oligoribonucleotides in which the O ⁶ of m²G is protected with a 2-(p-nitrophenyl)ethyl group.