A revision of the Peruvian species of Nasa ser. Alatae (Loasaceae)

The Nasa series Alatae is revised for Peru. Species limits in this group are re-investigated on the basis of modern collections, all types and extensive field studies. A total of 12 species are recognized, seven of them- N. dillonii, N. driesslet, N. nubicolorum, N. pascoensis, N. sagasteguii, N, anderssonii and N. urentivelutina -are described as new to science. All new, and two of the previously recognized species are illustrated by line drawings. The species of this group are from Andean habitats, mostly cloud forests, and nearly all of them are narrow endemics.     

A comparison of snRNP-associated Sm-autoantigens: human N, rat N and human B/B''.

N is a tissue-specific, Sm-epitope bearing, snRNP-associated protein found predominantly in brain. The cDNA sequence encoding human N is compared to those for rat N and human B/B'. The amino acid sequences of human and rat N are 100% conserved. Although the amino acid sequences of N and B/B' are very similar to each other, B/B' contains 50 amino acids which are not present in N. On Northern blots the cDNAs encoding N and B/B' recognize two different RNA species. A comparison of the codon usage, as specified by the open reading frames of N and B/B' as well as results from Southern blots, show that N and B/B' are derived from different genes.     

Immobilizing nitrogen to control plant invasion

Increased soil N availability may often facilitate plant invasions. Therefore, lowering N availability might reduce these invasions and favor desired species. Here, we review the potential efficacy of several commonly proposed management approaches for lowering N availability to control invasion, including soil C addition, burning, grazing, topsoil removal, and biomass removal, as well as a less frequently proposed management approach for lowering N availability, establishment of plant species adapted to low N availability. We conclude that many of these approaches may be promising for lowering N availability by stimulating N immobilization, even though most are generally ineffective for removing N from ecosystems (excepting topsoil removal). C addition and topsoil removal are the most reliable approaches for lowering N availability, and often favor desired species over invasive species, but are too expensive or destructive, respectively, for most management applications. Less intensive approaches, such as establishing low-N plant species, burning, grazing and biomass removal, are less expensive than C addition and may lower N availability if they favor plant species that are adapted to low N availability, produce high C:N tissue, and thus stimulate N immobilization. Regardless of the method used, lowering N availability sufficiently to reduce invasion will be difficult, particularly in sites with high atmospheric N deposition or agricultural runoff. Therefore, where feasible, the disturbances that result in high N availability should be limited in order to reduce invasions by nitrophilic weeds.     

Relieving substrate limitation-soil moisture and temperature determine gross N transformation rates

A field experiment was designed with the objective to reveal the interactions between soil moisture, temperature, total, dissolved, and phosphate buffer extractable C and N, and microbial activity in the control of in situ gross N mineralization and immobilization rates in a deciduous forest. We had three alternative hypotheses to explain variations of the gross N transformations: 1) microorganisms are C limited, 2) microorganisms are N limited, or 3) neither C nor N limit the microorganisms but moisture and temperature conditions. Each hypothesis had specific criteria to be fulfilled for its acceptance. The results demonstrated that gross N transformation rates were more dependent on and variable with soil moisture and temperature than the size of the different C and N pools. The immobilization of N was dependent on the gross mineralization rate, suggesting that the production of enzymes for mineralization of organic N and the immobilization of N from the surrounding soil is disconfirmed when the intracellular N content of the microorganisms is sufficiently high. If the microorganisms are starved for N, enzyme systems involved in both the assimilation and mineralization of N are activated. The mean in situ gross N mineralization rate was two orders of magnitude higher than the natural N deposition in the area and the N addition in the NITREX experiments, meaning that a reduction in the gross N mineralization rate of about 1% would be enough to compensate for the addition of inorganic N. This decrease would hardly be detectable given the great spatial and temporal variability of N transformation rates.     

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.     

Revision of the Natada fusca complex and description of six new neotropical species (Lepidoptera: Limacodidae)

Six new species in the genus Natada, which have been hidden under Natada fusca Druce, are described and defined primarily by genitalia. New species include N. burnsi, N. truncata, N. singulara, N. chaconi, N. covelli, and N. confusa. Five of eight species in the Natada fusca complex, which also includes N. fuscodivisa Dognin, occur in Costa Rica. Distribution of the complex ranges from Mexico to the upper Amazon Basin and Guianas. Detailed geographic information and multiple genitalic drawings of males of one species, N. confusa, are provided to help define and separate species. The lectotype and paralectotype of N. fusca are designated.     

中国萝潜蝇属分类研究 (双翅目: 潜蝇科)

研究了中国萝潜蝇属Napomyza Westwood,确认该属在我国现知下列6种：环萝潜蝇Napomyza annulipes (Meigen),角萝潜蝇N.hirticornis(Hendel),菊茎萝潜蝇N.lateralis (Fallen),拟土萝潜蝇N.paratripolii sp. Nov.,毛萝潜蝇N. plumea Spencer和西藏萝潜蝇N. xizangensis sp. Nov.。除描述二新种并附特征图外, 还提供中国已知种类的鉴别特征和分种检索表。     

delta(15)N as an integrator of the nitrogen cycle

Natural abundances of the rare stable isotope of nitrogen, 15N, are now being used widely in research on N cycling in organisms and ecosystems. 15N natural abundances are used in fundamentally different ways from traditional 15N tracers by integrating N cycle processes via N isotope fractionations and the mixing of various N-containing pools. This approach of using 15N natural abundances still requires certain technical and conceptual advances before it can be used routinely in ecological research. Here, the basis of the natural abundance 15N approach and opportunities for applying it in ecology are reviewed, and recent progress towards overcoming some of the key technical problems and in revealing large-scale patterns in N cycle processes is discussed.     

Nitrogen binding to deoxyhemoglobin at high pressures and its relation to changes in hemoglobin-oxygen affinity

The stoichiometric and thermodynamic properties of nitrogen (N2) binding to human deoxyhemoglobin (Hb) at N2 saturation pressures up to 400 atm were derived from measured N2 solubilities in protein-free buffers (pH 7.1) and in corresponding buffer + Hb (6.5% w/w) solutions at 20.0, 25.0, and 37.0 degrees C. At each temperature, approximately 3 N2 molecules bind per Hb tetramer at N2 pressures of 100 atm, while about 7 N2 molecules bind per tetramer at 400 atm N2 pressure, where available binding sites are still not fully saturated. Calculated N2-Hb binding isotherms are well described by a simple binding model with 12 independent and equivalent binding sites/Hb tetramer. N2 binding at each of the sites is hydrophobic, exhibiting the typical increase of the dissociation enthalpy with temperature. Enthalpies of dissociation are slightly more negative, while corresponding unitary entropies are somewhat less negative than those for the transfer of N2 from olive oil to water. Calculated partial molar volumes of N2 in Hb are positive but less than the corresponding partial molar volumes of N2 in buffer. Results indicate that N2 binding to Hb is accompanied by only small protein conformational changes which entail slight structural destabilization and loss of free volume in the protein that partially accommodates the volume of the N2 ligand. Results are related to previously reported effects of high pressure and high-pressure N2 on HbO2 affinity, illuminating essential features of the molecular mechanisms for these effects.     

Global pollution of surface waters from point and nonpoint sources of nitrogen

Global 0.5- by 0.5-degree resolution estimates are presented on the fate of nitrogen (N) stemming from point and nonpoint sources, including plant uptake, denitrification, leaching from the rooting zone, rapid flow through shallow groundwater, and slow flow through deep groundwater to riverine systems. Historical N inputs are used to describe the N flows in groundwater. For nonpoint N sources (agricultural and natural ecosystems), calculations are based on local hydrology, climate, geology, soils, climate and land use combined with data for 1995 on crop production, N inputs from N fertilizers and animal manure, and estimates for ammonia emissions, biological N fixation, and N deposition. For point sources, our estimates are based on population densities and human N emissions, sanitation, and treatment. The results provide a first insight into the magnitude of the N losses from soil-plant systems and point sources in various parts of the world, and the fate of N during transport in atmosphere, groundwater, and surface water. The contribution to the river N load by anthropogenic N pollution is dominant in many river basins in Europe, Asia, and North Africa. Our model results explain much of the variation in measured N export from different world river basins.     

新疆菱形藻属和细齿藻属(硅藻门)中国新记录植物

2001年7月至8月、2007年7月分别两次在新疆各地采集硅藻标本,经显微观察,共鉴定出菱形藻属和细齿藻属(硅藻门)中国新记录植物11种1变种,其中菱形藻属9种:额雷菱形藻(Nitzschia eglei Lange-Bertalot)、弯曲菱形藻(N.flexa Schumann)、多样菱形藻(N.diversa Hustedt)、化石菱形藻[N.fossilis (Grunow) Grunow]、吉斯纳菱形藻(N.gessneri Hustedt)、平庸菱形藻(N.inconspicua Grunow)、辐射菱形藻(N.radicula Hustedt)、常见菱形藻(N.solita Hustedt)和粗肋菱形藻(N.valdecostata Lange-Bertalot & Simonsen);细齿藻属2种1变种:科瑞提细齿藻[Denticula creticola (strup) Lange-Bertalot & Krammer]、库津细齿藻汝牧变种(D.kuetzingii var.rumrichae Krammer)和强壮细齿藻[D.valida (Pedicino) Grunow].并对其12种新记录植物的分类学特征进行了详细的描述.     

采伐和火烧对森林氮动态的影响

森林是重要的陆地生态系统类型,它通过特有的养分循环机制维持其结构和功能.其中氮素对林木生长和发育十分重要,而且常是森林生产力的限制因素.另一方面,森林氮动态又常受到人类活动干扰的影响.根据国内外研究结果综述了采伐和火烧对森林氮动态的影响.结果表明采伐后环境因素的变化将影响森林N动态,其中最为关注的是采伐后一系列因素引起的N损失,如:N淋溶增加、伴随生物量的N迁移以及因径流或侵蚀增加造成的枯枝落叶层和土壤层N流失.这些N损失又将影响更新林分的生长和生产力.此外,采伐后N吸收速率一般下降,但随着植被快速生长N吸收速率将不断增加.采伐后氨化和硝化过程增强,但因短期内同化作用较弱,生态系统中大部分N将发生损失.火烧对森林N动态的短期影响主要包括:第一,火烧时N直接挥发损失;第二,火烧后N有效性增加,这主要由灰分沉积、根和微生物死亡及有机质N矿化增强等综合造成.随着时间延长,N有效性逐渐降低,这可能与火烧引起的有机质损失、植物N吸收增加、淋溶或侵蚀损失有关.然而,目前关于火烧造成的长期生态影响,如火烧后地上植被恢复与地下生物地球化学过程变化有何联系仍不太清楚.未来研究应着重于探讨氮素对森林采伐和火烧作出的短期响应将如何长期影响森林的结构和功能.此外,建议在实施营林方案时需考虑采伐和火烧对生态系统氮的影响.     

Antler hyphae and the physical properties of the peridiole wall in the genus Nidula

Several physical properties of the peridiole wall of the four species of Nidula are shown to be related to the presence of thick–walled pigmented antler hyphae. The peridiole wall of N. emodensis and N. niveotomentosa is strongly hydrophobic and markedly frangible: in these species antler hyphae form the outermost layer of peridioles. In N. Candida and N. macrocarpa , antler hyphae are located beneath an outer bounding layer of undifferentiated and unpigmented hyphae and the peridioles of these species are hydrophilic and their walls are not frangible. Splash experiments indicate that the fruit bodies of N. emodensis and N. niveotomentosa are more efficient in splash dispersal of peridioles than fruit bodies of N. Candida.     

A revision of Neomegalotomus (Hemiptera: Alydidae)

We recognize two species in Neomegalotomus, N. parvus (Westwood), the type species; and N. rufipes (Westwood). The two species are redescribed from type specimens, and are keyed. We synonymize the following species with Neomegalotomus parvus: N. simplex (Westwood), N. latifascia (Berg), and N. pallescens (St?l) (all new synonymies). We synonymize N. jamaicensis (Westwood) with N. rufipes (new synonymy). The type specimens of all species hitherto placed in the genus are also redescribed, except those of N. debilis (Walker) and N. vicinus (Westwood). N. parvus occurs from México through Central America into northern Argentina and east into Venezuela and adjacent Caribbean islands. N. rufipes is widespread in the Caribbean south towards Venezuela. The two species overlap in distribution: N. parvus is found on St. Vincent and Tobago, whereas N. rufipes occurs on Grenada, which lies between those two islands.     

The participation of cytochromes in the reduction of N20 to N2 by a denitryfying bacterium.

The oxidation of cytochromes during the reduction of N2O to N2 by a denitrifying bacterium was studied spectrophotometrically. The reduced b- and c-type cytochromes are partially oxidized when N2O is added to intact cells reduced with lactate under anaerobic conditions. The oxidation of cytochromes is inhibited non-competitively by azide, cyanide, 2,4-dinitrophenol and CuSO4, which inhibit the reduction of N2O to N2. In the presence of each inhibitor at a high concentration, at which the reduction of N2O to N2 is perfectly inhibited, cytochromes are not oxidized by N2O, while when an adequate, low concentration of inhibitor is added, b-type cytochrome is partially oxidized but c-type cytochrome is apparently not oxidized. In cell-free extracts, prepared by the sonic disruption of cells, that have entirely lost their activity in the reduction of N2O to N2, cytochromes are not oxidized by N2O. From the above results, it was concluded that b-type and c-type cytochromes should participate in the electron transport mechanism of the reduction of N2O to N2.     

Two-dimensional fast transforms applied to memory limited disk operating computers.

Two-dimensional transform algorithms are usually impractical to small machines which cannot handle N2 real (or complex) data points in core when N is large. Storing the input data in N disk records and computing two sequential one-dimensional transforms requires N(N + 3) disk access and 2 N applications of the one-dimensional procedure. Expanding the fast one-dimensional algorithm it is suggested that only 2 N log2N disk accesses are needed whereas the one-dimensional procedure is activated only N times.     

Use of the spot, plate and suspension test systems for the detection of the mutagenicity of environmental agents and chemical carcinogens in Neurospora crassa.

N23 and N24, selected from hundreds of ad-3 mutants, have been used as testers for the spot, plate and suspension tests in Neurospora crassa. These two testers are highly sensitive to mutagens and are revertible by a specific group of chemicals. N23 can be reverted from an adenine-dependence to adenine-independence by agents which cause base-pair substitutions whereas N24 can be reverted by frameshift mutagens. Studies described here show that spot, plate and suspension tests using testers N23 and N24 are satisfactory substitutes for the ad-3 forward-mutation system for screening the mutagenic activity of environmental agents and chemical carcinogens in N. crassa.     

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