Effect of infiltration rate on nitrogen dynamics in paddy soil after high-load nitrogen application containing N tracer

Flooded paddy fields perform many ecological and conservation functions and are also reported to facilitate livestock waste disposal. Paddy field infiltration rates are important for nitrogen dynamics. A laboratory study was conducted to compare the effects of infiltration rate on nitrogen dynamics including nitrogen leaching, soil adsorption, microorganism assimilation, plant uptake and denitrification. Two infiltration rates were applied to paddy soil: 18.6 ± 10.3 mm d⁻¹ (High Infiltration Columns: HIC) and 4.49 ± 3.15 mm d⁻¹ (Low Infiltration Columns: LIC). Total nitrogen load was 484 kg-N ha⁻¹, with the ammonium ion form including basal fertilizer and a double supplemental fertilizer application. A (¹⁵NH₄)₂SO₄ tracer was applied in each infiltration rate as supplemental fertilizer.Nitrification and denitrification, plant uptake, soil adsorption, and leaching differed between infiltration rates. Compared with high nitrate concentration in HIC soil water, little nitrate appeared in the LIC, and it maintained relatively higher soil water ammonium concentrations long after application. The ¹⁵N assimilated by rice and contained in the LIC soil was higher than in the HIC, suggesting that low infiltration is beneficial to nitrogen assimilation, adsorption and fixation. Although loss of nitrogen via leaching was higher in the HIC than the LIC, it accounted for only 3.94% of total ¹⁵N input. About 69.4% of total ¹⁵N input was unaccounted for in the HIC, whereas 38.3% of total ¹⁵N input was unaccounted for in the LIC. According to the denitrification rate calculated from changes in ²⁹N₂/²⁸N₂ and ³⁰N₂/²⁸N₂ ratios, the denitrification rate after HIC application was higher than the LIC, reaching a maximum rate of 2.9 g m⁻² d⁻¹. This suggests that high infiltration rate enhances nitrification and denitrification, with most of the unaccounted inputted ¹⁵N in the HIC was probably lost through nitrification and denitrification.     

A network analysis of plant–pollinator interactions in temperate rain forests of Chiloé Island, Chile

This study characterizes the structure of a plant–pollinator network in a temperate rain forest of Chiloé Island, southern Chile, where woody species are strongly dependent on biotic pollinators, and analyzes its robustness to the loss of participating species. Degree distribution, nestedness, and expected species persistence were evaluated. In addition, we assessed the roles of predefined subsets of plants (classified by life forms) and pollinators (grouped by taxonomic orders) in the network’s structure and dynamics. For this, we simulated the complete removal of each plant and pollinator subset and analyzed the resultant connectivity patterns, as well as the expected long-term species losses by running a stochastic model. Finally, we evaluated the sensitivity of the network structure to the loss of single species in order to identify potential targets for conservation. Our results show that the plant–pollinator network of this Chilean temperate rain forest exhibits a nested structure of interactions, with a degree distribution best described by a power law model. Model simulations revealed the importance of trees and hymenopterans as pivotal groups that maintain the core structure of the pollination network and guarantee overall species persistence. The hymenopterans Bombus dahlbomii and Diphaglossa gayi, the shrubs Tepualia stipularis and Ugni molinae, the vines Mitraria coccinea and Asteranthera ovata, and the entire set of tree species exerted a disproportionately large influence on the preservation of network structure and should be considered as focal species for conservation programs given current threats from selective logging and habitat loss.     

太湖地区稻田氮肥吸收及其利用的研究

The effects of different amounts and kinds of nitrogen fertilizer on rice yield and its nitrogen uptake and utiliza-tion were studied on a main paddy soil (Wushan soil) of Taihu area. The results indicated that the optimal amount of nitrogen fertilizer was about 180 kg N· hm^-2 for rice production. Applying ammonium sulfate was better than applying urea for increasing rice yield. The efficiency of nitrogen fertilizer in this experiment was about 41.8-48.5%, and its loss was 22.8-38.1% .     

不同海拔生境条件下水稻叶片及茎鞘氮素含量的变化

本文报道生长在不同海拔生境条件下(云南省元江、玉溪、昆明、大理、丽江)的水稻叶片及茎鞘氮素含量的变化。所获得的主要结果如下: 1.自然生境条件下,水稻叶片和茎鞘的氮素含量随着生育期的进展而变化,有一个由高到低的下降趋势。而前期低海拔地区的含量比高海拔地区的高,成熟期则是海拔越高其叶片含氮量也越高,茎鞘含氮量的情形与叶片相反。 2.穗肥施用时期不同,对叶片和茎鞘氮素含量的影响不同,在低和较低海拔地区施用时期越晚,成熟期残存于叶片及茎鞘的氮素就越多;而且海拔高的地区的含量也高。在冷凉的高海拔地区丽江以颖花分化期追肥比幼穗分化和减数分裂期施用则黄熟期保持较高的含氮量。     

互惠共生微生物：新资源，新技术，新机遇，新挑战

2020年9月联合国环境规划署发布《全球生物多样性展望-5》(GBO-5)报告,助力世界实现协商一致的愿景——到2050年“与自然和谐相处”。其实,原本地球上的所有生物都是相互依存、互惠共生于地球村的,尽管存在少数“坏分子”。但由于人类的贪婪,过度扩张才导致地球“千疮百孔”的面貌,严重威胁到人类文明可持续发展。通过最近20年的研究,互惠共生微生物(mutualistic symbiotic microbes,MSM)从其丰富的群落多样性到种质新资源、从多种多样的生理生态功能到作用机制、从基础探究到新技术研发,为实现人与自然和谐相处的愿景提供了新机遇,同时也面临新挑战。令人可喜的是,中国在MSM研究领域取得了令世人瞩目的成果。《微生物学通报》于2020年11期特别推出了“互惠共生微生物专栏”,旨在展现中国MSM研究的最新进展和成果,促进生物共生学的发展壮大。     

互惠共生微生物多样性研究概况

所谓互惠共生微生物(mutualistic symbiotic microbes,MSM)是指能定殖其他生物构建互惠共生体系的微生物,主要包括互惠共生细菌、互惠共生放线菌和互惠共生真菌等.MSM种类繁多、分布广泛、物种多样性丰富,涉及原核生物界和真菌界等.MSM定殖人体、动物、植物、藻类或其他真菌,可构建各自相应的互惠...     

Cellular interaction through LewisX cluster: theoretical studies

It is well known that cell surface carbohydrates play a role in cell–cell adhesion and communication. LewisX glycosphingolipids form microdomains on cell surfaces. Homotypic and calcium-mediated LewisX–LewisX (LeX-LeX) interactions were proposed to be responsible for the initial steps of cell adhesion, and to mediate embryogenesis and metastasis. Various techniques have been used to investigate such interactions, but little information is available on the geometry and the mechanism of dimerisation. To better understand these interactions, a new molecular model was developed to simulate homotypic interactions in explicit solvent with and without calcium ions. Accurate analysis of both trajectories yielded valuable information about the energetics of LeX-LeX dimerisation. Detailed interpretation of the hydrogen bond network and the presence of calcium ions along the trajectory provide valuable insights into the role of calcium ions in this carbohydrate–carbohydrate interaction. Figure Calcium population density around the LewisX carbohydrate (after the trajectory has been fitted to the primary unit cell). All central dimer coordinates are fitted along the time axis, whereas calcium ion positions are recorded and represented as points. The clouds of points indicate that the ions are not randomly placed around the dimer but take up preferred positions     

Differences in carbon and nutrient fractions among arctic growth forms

Summary In a survey of 28 plant species of 6 major growth forms from Alaskan tundra, we found no consistent difference among growth forms in the chemical nature of stored reserves except for lichens and mosses (which stored C primarily as polysaccharides) and shrubs (which tended to store C more as sugars than as polysaccharides). Forbs and graminoids showed particularly great diversity in the chemical nature of stored reserves. In contrast, C, N, and P chemistry of leaves was strikingly similar among all species and growth forms. Concentrations of stored reserves of C, N, and P were highest and showed greatest seasonal fluctuations in forbs and graminoids but were relatively constant in evergreen shrubs. From this information, we draw three general conclusions: (1) the photosynthetic function of leaves strongly constrains leaf chemistry so that similar chemical composition is found in all species and growth forms: (2) the chemical nature of storage reserves is highly variable, both within and among growth forms; (3) the concentration and seasonal pattern of storage reserves are closely linked to growth-form and reflect growth-form differences in woodiness, phenology, and relative dependence upon concurrent uptake vs. storage in support of growth.     

The utility of residual dipolar couplings in detecting motion in carbohydrates: application to sucrose

The solution structure and dynamics of sucrose are examined using a combination of NMR residual dipolar coupling and molecular mechanics force fields. It is found that the alignment tensors of the individual rings are different, and that fitting 35 measured residual dipolar couplings to structures with specific phi, psi values indicates the presence of three major conformations: phi, psi=(120 degrees ,270 degrees), (45 degrees, 300 degrees) and (90 degrees ,180 degrees). Furthermore, fitting two structures simultaneously to the 35 residual dipolar couplings results in a substantial improvement in the fits. The existence of multiple conformations having similar stabilities is a strong indication of motion, due to the interconversion among these states. Results from four molecular mechanics force fields are in general agreement with the experimental results. However, there are major disagreements between force fields. Because fits of residual dipolar couplings to structures are dependent on the force field used to calculate the structures, multiple force fields were used to interpret NMR data. It is demonstrated that the pucker of the fructofuranosyl ring affects the calculated potential energy surface, and the fit to the residual dipolar couplings data. Previously published 13C nuclear relaxation results suggesting that sucrose is rigid are not inconsistent with the present results when motional timescales are considered.     

CONDORR—CONstrained Dynamics of Rigid Residues: a molecular dynamics program for constrained molecules

A computer program CONDORR (CONstrained Dynamics of Rigid Residues) was developed for molecular dynamics simulations of large and/or constrained molecular systems, particularly carbohydrates. CONDORR efficiently calculates molecular trajectories on the basis of 2D or 3D potential energy maps, and can generate such maps based on a simple force field. The simulations involve three translational and three rotational degrees of freedom for each rigid, asymmetrical residue in the model. Total energy and angular momentum are conserved when no stochastic or external forces are applied to the model, if the time step is kept sufficiently short. Application of Langevin dynamics allows longer time steps, providing efficient exploration of conformational space. The utility of CONDORR was demonstrated by application to a constrained polysaccharide model and to the calculation of residual dipolar couplings for a disaccharide.Figure Molecular models (bottom) are created by cloning rigid residue archetypes (top) and joining them together. As defined here, the archetypes AX, HM and BG respectively correspond to an -d-Xylp residue, a hydroxymethyl group, and a -d-Glcp residue lacking O6, H6a and H6b. Each archetype contains atoms (indicated by boxes) that can be shared with other archetypes to form a linked structure. For example, the glycosidic link between the two d-Glcp residues is established by specifying that O1 of the nonreducing -d-Glcp (BG) residue (2) is identical to O4 of the reducing Glcp (BG) residue (1). The coordinates of the two residues are adjusted so as to superimpose these two (nominally distinct) atoms. Flexible hydroxymethyl (HM) groups (3 and 4) are treated as separate residues, and the torsional angles (normally indicated by the symbol ) that define their geometric relationships to the pyranosyl rings of the BG residues are specified as ₃ and ₄, respectively. The torsional angles ₃ and ₄, defined solely to maintain the orientation of the geminal H-atoms of the hydroxymethyl group, are not shown. (See text.) The illustrated trisaccharide is thus specified as a collection of 5 residues which are represented by 3 archetypes. Models of the disaccharide cellobiose (-d-Glcp-(14)-d-Glcp) must include residues 1 and 2, but the hydroxymethyl groups (residues 3 and 4) can also be explicitly included in this model     

Habitat destruction in mutualistic metacommunities

We investigate a mutualistic metacommunity where the strength of the mutualistic interaction between species is measured by the extent to which the presence of one species on a patch either reduces the extinction rate of the others present on the same patch or increases their ability to colonize other patches. In both cases, a strong enough mutualism enables all species to persist at habitat densities where they would all be extinct in the absence of the interaction. However, a mutualistic interaction that enhances colonization enables the species to persist at lower habitat density than one that suppresses extinction. All species abruptly go extinct (catastrophe) when the habitat density is decreased infinitesimally below a critical value. A comparison of the mean field or spatially implicit case with unrestricted dispersal and colonization to all patches in the system with a spatially explicit case where dispersal is restricted to the immediate neighbours of the original patch leads to the intriguing conclusion that restricted dispersal can be favourable for species that have a beneficial effect on each other when habitat conditions are adverse. When the mutualistic interaction is strong enough, the extinction threshold or critical amount of habitat required for the persistence of all species is lower when the dispersal is locally restricted than when unrestricted ! The persistence advantage for all species created by the mutualistic interaction increases substantially with the number of species in the metacommunity, as does the advantage for restricted dispersal over global dispersal.     

Nitrogen transformation processes in relation to improved cultural practices for lowland rice

Summary Inappropriate method and timing of N fertilizer application was found to result in 50–60% N losses. Recent nitrogen transformation studies indicate that NH₃ volatilization in lowland rice soils is an important loss mechanism, causing a 5–47% loss of applied fertilizer under field conditions. Estimated denitrification losses were between 28 and 33%. Ammonia volatilization losses from lowland rice can be controlled by i) placement of fertilizer in the reduced layer and proper timing of application, ii) using phenylphosphorodiamidate (PPD) to delay urease activity in flooded soils, and iii) using algicides to help stabilize changes in floodwater pH. Appropriate fertilizer placement and timing is probably the most effective technique in controlling denitrification at the farm level. The effectivity of nitrification inhibitors as another method is still being evaluated. With 60–80% of N absorbed by the crop derived from the native N pool, substantial yield gains in lowland rice are highly possible with resources already in the land. Extensive studies on soil N and its management, and an understanding of soil N dynamics will greatly facilitate the decrease in immobilization and ammonium fixation in the soil and the increase in N availability to the rice crop. Critical research needs include greater emphasis on N transformation processes in rainfed lowland rice which is grown under more harsh and variable environmental regimes than irrigated lowland rice.     

开放式空气CO2浓度增高对水稻N素吸收利用的影响

在大田栽培条件下 ,研究空气中CO2 浓度增高 (FACE) 2 0 0 μmol·mol-1对水稻N素吸收及其利用效率的影响 .结果表明 ,FACE处理使水稻不同生育时期的植株含N率显著下降 ;由于干物质生产量显著增大 ,FACE处理使水稻不同生育时期的N素累积量有所提高 ,但无显著影响 ;FACE处理能够显著提高移栽后 2 8d、抽穗期以及成熟期单位N素的干物质生产效率、单位N素的籽粒生产效率和显著提高水稻的N素收获指数 .高N处理的植株含N率、N素累积量均有所增加 ,但使N素生产效率呈现下降趋势 .     

虫生真菌蝉拟青霉的研究

观察了蝉拟青霉的无性世代,在24℃下载片培养结果,分生孢子经8hr萌发,24hr普遍形成菌丝,36hr出现产孢结构和产生次代分生孢子。该菌生长合适温度24—26℃,分生孢子萌芽要求相对湿度在90%以上。pH4—12范围均见生长,但以5—6为佳。对10种碳源和9种无机氮源利用检测结果,用葡萄糖作碳源孢子产量高,用果糖作碳源菌丝体产量高。不利用菊糖、L-山梨糖、L-鼠李糖。对KNO_3利用佳,但不能利用NaNO_2,和硫脲。该菌能较强抗紫外辐射。