宁夏陆地生态系统水分利用效率特征及其影响因子

生态系统水分利用效率(Water Use Efficiency, WUE)是表征生态系统碳水耦合程度的重要指标,能反映生态系统碳水循环规律及其相互作用关系。基于MODIS数据以及宁夏生态系统类型数据,分析2000—2017年宁夏不同生态系统WUE的变化特征,探讨了NPP和ET两种因子对WUE年际与年内变化的影响。结果表明:(1)全区陆地生态系统的年均WUE为1.03 g·C/kg·H_2O,值域在0.55—2.98 g·C/kg·H_2O之间,总体上呈现南北高、中部低的特征。(2)不同生态系统的WUE差异较大,由高到低为水体及湿地、森林、农田、草地、聚落、荒漠和其他生态系统,在同类生态系统中,植被生物量和盖度越高的亚类生态系统,其WUE也越高。(3)宁夏陆地生态系统WUE存在着每年0.0141 g·C/kg·H_2O的下降趋势,年内WUE呈典型的单峰形态,变化范围在0.02—2.16 g·C/kg·H_2O之间。(4)年际尺度上,宁夏陆地生态系统WUE与年蒸散(Evapotranspiration,ET)有极显著负相关性(P0.01),而与净初级生产力(Net Primary Production,NPP)没有相关性;年内尺度上,WUE变化与ET呈显著正相关(P0.05),与NPP呈极显著正相关(P0.01),这与植被的年内季节性生长过程有关。(5)根据ET强弱和WUE高低,可将宁夏陆地生态系统水分利用效率特征划分为4类,即低ET低WUE区、低ET高WUE区、高ET低WUE区和高ET高WUE区。宁夏的生态恢复工程在增强植被生产力的同时,也增强了区域水分消耗,致使陆地生态系统整体水分利用效率下降,这为宁夏未来水资源调控和生态重建提供了科学依据。     

2000-2015年宁夏草地净初级生产力时空特征及其气候响应

草地是宁夏陆地生态系统的重要组成部分,估算其净初级生产力（NPP）对宁夏草地可持续利用与管理至关重要。采用MODIS数据和CASA模型对2000-2015年间宁夏草地生态系统NPP进行了估算,通过一元线性回归趋势分析、Hurst指数等方法研究草地NPP的时空变化规律及未来演变趋势,并分析草地NPP与气象因子的相关性。结果表明：（1）基于CASA模型的宁夏草地NPP模拟精度高,其估算值与实测多年草地NPP均值具有良好的线性关系（R=0.93,P < 0.01）,与MOD17产品的草地NPP空间分布基本一致。（2）近16 a宁夏草地年均NPP为148.28 g C m^-2 a^-1,且存在波动上升的趋势,其线性增长率为3.84 g C m^-2 a^-1（P < 0.01）。（3）宁夏草地NPP整体处于上升趋势,草地NPP增长的草地面积达98%,且其增率自南向北递减;宁夏草地NPP的Hurst指数在0.27-0.81之间,均值为0.53,大部分草地的NPP变化趋势具有较强同向持续性。（4）在年时间尺度上,宁夏草地NPP主要受降水量的影响,与气温的相关性较弱;在月时间尺度上,生长季草地NPP与月总降水量的相关性高,且不存在时间滞后响应现象,而与月均温的响应则存在1个月的时间滞后性,宁夏大面积分布的干草原与荒漠草原NPP对气温响应滞后是导致这一现象发生的主要原因。     

松材线虫的天然毒素研究进展

概述了松材线虫病的现行防治措施及存在问题,介绍了植物源和真菌源天然毒素毒杀松材线虫的研究现状及研究中遇到的问题,指出天然毒素在未来松材线虫病生物防治中的研究方向。     

嗜热链球菌MGB80-7所产胞外多糖的表型结构及其抗氧化活性

【背景】胞外多糖（exopolysaccharide,EPS）是乳酸菌生长代谢过程中所产生的一种次级代谢产物,除了可以改善产品质构和品质外,其生理功能也是近年来研究人员追捧的热点。【目的】探究乳酸菌EPS的表征特性和分子结构,揭示其与EPS益生特性之间的联系。【方法】以产EPS的嗜热链球菌（Streptococcus thermophilus,S. thermophilus） MGB80-7为研究对象,利用苯酚-硫酸法测定菌株EPS产量。采用离子交换柱层析和凝胶分子筛层析对该菌株所产EPS进行分离纯化,结合凝胶色谱、红外光谱及高效液相色谱对EPS表型结构进行剖析。此外,为确定EPS表型特征对其抗氧化活性的影响,测定了EPS对超氧阴离子、羟自由基及DPPH自由基等的清除能力。【结果】S. thermophilus MGB80-7在M17培养基中EPS产量较高,为（268.25±5.36） mg/mL,分离纯化后共得到2种多糖组分,其中中性多糖（WPS-807）分子量为1.028×10⁵ Da,主要由葡萄糖、半乳糖和甘露糖组成,并含有少量的鼠李糖和阿拉伯糖,酸性多糖（...     

Influence of intra-tree variation in time of budburst of white spruce on herbivory and the behaviour and survivorship of Zeiraphera canadensis

Abstract.

• 1 Field studies were carried out to determine the effects of intra-tree variation in the time of budburst of white spruce, Picea glauca Moench (Voss.), on the behaviour and survivorship of, and herbivory by, the spruce bud moth, Zeiraphera canadensis Mutt. & Free.
• 2 There was significant variation in the time of budburst among whorls, shoots and buds. Budburst was acropetal, with buds in the interior of the lower crown bursting first and terminal buds on terminal shoots in the upper crown bursting last.
• 3 Bud moths laid the greatest proportion of their eggs in the middle of the crown and egg hatch was usually best synchronized to budburst in this region. Many eggs hatched before terminal buds on terminal shoots in the upper crown had burst and thus intra-tree variation in budburst decreased the probability that first-instar larvae would colonize the most important plant parts for growth.
• 4 However, many later instars dispersed upwards and outwards in the crown and colonized the late bursting buds in the upper crown. Such dispersal reduces the effectiveness of intra-plant variation in budburst to reduce herbivory and permits Z.canadensis to eat young nutritious buds for a longer period of time.
• 5 Intra-tree variance in the date of budburst was greater than that between trees but there were no consistent differences between the intra-tree variance of trees in half-sib families with high or low susceptibility to Z.canadensis. Differences between trees in herbivory, bud moth density and survivorship were not related to the amount of intra-tree variation in budburst.

     

El Niño and tree growth near Jerusalem over the last 20 years

A strong correlation is observed between an El Niño index (anomalies in tropical Pacific sea surface temperature) and rainfall in the Judean foothills near Jerusalem over the past 20 years. These relationships clearly influenced the growth of local pine trees, as reflected in the width of their annual tree rings. The ability to predict El Niño events about a year in advance lend a special significance to relationships reported here for ecology, agriculture and water management in this climatic transition zone. To help explain the observed, long-range teleconnection we propose a possible mechanism based on a newly identified direct cloud connection between equatorial Africa (more directly affected by El Niño) and the Southeastern Mediterranean shoreland. The penetration and contribution of the moisture current from equatorial Africa to this region may depend on a shift in the usual rain generating moisture currents to southwesterly trajectories (passing over north Africa). The occurrence of such shifts is supported by the observed decrease in the mean ¹⁸O content of the local precipitation during El Nino winters.     

Studies on Unequal Cleavage in Sea Urchins II. Surface Differentiation and the Direction of Nuclear Migration

Cortical features of the meso- and macromeres differ from those of the micromeres in sea urchins. At the end of the 8-cell stage, the four animal cells have a continuous row of vesicles lining the free surface of the cell by transmission electron microscopy (TEM) and the nuclei and the resulting mitotic apparatuses (MA) remain at the cell centers and eventually divide equally into eight mesomeres. In the four vegetal cells, narrow gaps can be seen in the vesicular rows near the vegetal pole. The resting nuclei migrate to these gaps and on forming the spindles, they point directly to the gaps. The result is formation of vesicle-free micromeres and vesicle-covered macromeres by unequal divisions.     

Body Form and Locomotion in Sharks

A revised interpretation of the mode of action of the heterocercaltail in sharks shows that the upturned tail axis tends to producea thrust directed downwards behind the centre of balance ofthe fish and thus gives a moment turning the head upwards. Thisis countered in two ways—by the rotation of the tail alongits longitudinal axis during each lateral beat, and throughthe action of the ventral hypochordal lobe. The shape of thetail and the mode of action of the tail in all sharks so farconsidered reflects a balance between these three factors, inall of them the net effect being the production of a forwardthrust from the tail that passes directly through the centreof balance of the fiish. There is normally therefore no tendencyfor the fish to turn around the centre of balance in a sagittalplane but there is a net sinking effect that is countered bythe planning effect of the pectoral fins and the ventral surfaceof the head. A study of 56 species of sharks shows that the tail is constructedaccording to a remarkably consistent common plan, the extremesbeing the high angled rather symmetrical tail of pelagic sharkssuch as hums, Lamna and Rhincodon and the straight tails ofbenthic sharks such as Ginglymostoma in which a ventral hypochordallobe is absent. When the general body shape of sharks, includingthe position of insertion of the median and paired fins andthe pattern of growth of fin surface areas is considered, theuniformity of the shark body plan and locomolor function isfurther emphasised. Four patterns of body form in sharks are recognised: 1) Thefast swimming pelagic sharks and the whale sharks have a tailwith a high aspect ratio, a conical head, a lateral fluke onthe caudal peduncle. 2) The generalised sharks typified by theCarcharhinidae, have lower heterocercal angles, a flattenedventral surface on the head and lack the caudal fluke. 3) Thedemersal sharks typified by the catsharks (Scyliorhinidae) havea very low, almost straight tail. The ventral hypochordal lobeis absent and the first dorsal fin is posterior in position.4) The squalomorph sharks are distinct in the absence of theanal fin, presence of a marked epicaudal lobe in the tail andoften an elevated insertion of the pectorals. The anal and second dorsal fins are always the smallest finsand the pectorals grow at the fastest rate. In general thereis an inverse relationship between size and rale of growth ofall fins and the ventral surface of the head. In hammerheadsthe growth data confirms that the head has a significant planingaction in swimming. The pectoral, second dorsal and anal finsshow an extreme constancy of position of insertion in all sharksstudied. The locomotor mechanism of sharks is adapted for anefficient cruising swimming but at the same time, the potentialinstability in the sagittal plan allows for the production ofturning moments that are used in attack and feeding.     

Studies on Unequal Cleavage in Sea Urchins III. Micromere Formation under Compression

When sea urchin embryos at 2-cell stage are flattered between agar plates, the direction of cleavage is rotated by 90° in each division in reference to the preceding cleavage and no micromere is formed. But under this condition, micromeres are formed in 2 cases; 1) When the egg axis is parallel to the plane of flattening, 2 micromeres are formed on one side of a square 16-cell stage. 2) when the egg axis is perpendicular to the plane, 4 micromeres are formed at the center of the square.
When put into a groove, a string of 4 cells is formed showing that the spindle direction is further deflected by the groove. In the following 16-cell stage in the groove, which consists of 2 layers of 8 cells, cases with 2 micromeres on one side and 4 micromeres at the center are still found. If the 2-cell stage is introduced into a groove after the formation of mitotic apparatus, the spindle direction can no longer be changed and the 4-cell stage becomes like 4 pancakes stuck in 2 layers, indicating that 2 asters are holding the ends of a spindle in fixed positions.     

SPERMIOGENESIS IN THE PULMONATE SNAIL,EUHADRA HICKONIS III. FLAGELLUM FORMATION*

The formation of the flagellum in the spermatid of the Japanese land snail, Euhadra hickonis, is introduced by the appearance of a central indentation in the differentiated posterior side of the spherical nucleus early in spermiogenesis. One centriole moves to this part of the cell, changes in several structural respects and acquires a short-lived “centriole adjunct”. At first it lies tangential to the nuclear surface as it begins to induce formation of the flagellar axoneme; then it turns so that its proximal end fits into the deepening nuclear indentation (“implantation fossa”). Cytoplasmic tubules appear to mediate this shift in direction. Internal changes in the centriolar components begin as it initiates formation of the axoneme, and continue throughout spermiogenesis. First, a dense “cap” forms at its proximal end, the microtubular triplets become doublets and a pair of singlets occupies the center of the complex. All these microtubules extend from the dense cap and are continuous with those of the axoneme. As the basal body (modified centriole) becomes set in the implantation fossa, the material of the centriole adjunct forms 9 strands, which are continuous with the peripheral coarse fibers when these develop. The microtubular doublets of the basal body are visible for a short time between the fiber strands; in the mature spermatozoon they are found embedded in the basal body portions of the coarse fibers in a degenerated form. Posterior to the basal body, however, they separate from the inner sides of the striated coarse fibers and become the doublets of the axoneme. The proximal part of the elongating axoneme lies in a posterior extension of the cell, in which glycogen particles and mitochondria are conspicuous. As the mitochondria unite into a sheath tightly surrounding the axoneme, the structure of their cristae changes to form a paracrystal-line “mitochondria derivative”, which consists of many layers close to the nucleus and progressively fewer posteriorly. Outside of this “primary sheath”, more modified mitochondria unite to form a “secondary sheath” of paracrystalline lamellae which encloses a compartment, filled with glycogen particles, that extends in a low-pitched helix nearly to the end of the flagellum. In the late spermatid, microtubules become arranged at regular intervals around the nucleus and secondary sheath of the flagellum for a short period while the remaining cytoplasm and spermatid organelles such as the Golgi complex are being discarded. The flagellum of the mature spermatozoon is 250–300 μm in length, tapering gradually from a diameter of ca 1 μm just behind the nucleus to less than 0.3 μm at its tip, as the result of reduction in the amount of stored glycogen, the number of paracrystalline lamellae and the diameter of the peripheral fibers.