辽东栎的繁殖体及其与种群更新的关系

就辽东栎的种子雨及其传播动力、种子传播后的命运、种子萌发、幼苗建立、实生更新对动物捕食的适应和萌生特性等方面进行了简要综述,并对未来研究的发展方向进行了展望。辽东栎种子是多种脊椎动物和鸟类的食物资源,种子萌发和幼苗形成期间的捕食压力导致其实生更新困难,但捕食动物对种子的搬运和埋藏对辽东栎种群更新和扩散具有重要意义;光照和水分对辽东栎的种子萌发和幼苗建立都具有重要影响,在森林管理工作中,适当干扰 (例如择伐) 对辽东栎的种子萌发、幼苗生长与存活以及种群更新都是有利的。较强的萌生能力对维持辽东栎的遗传多样性和种群活力具有重要的生态学意义;在强干扰条件下,萌生作为辽东栎通过从种子、幼苗、幼树到成年植株过程中的更新瓶颈的途径,是辽东栎实现种群更新的主要对策。     

小型啮齿动物对小兴安岭5种林木种子扩散的影响

在小兴安岭地区研究了林鼠对胡桃楸(Juglans mandshurica)、毛榛(Corylus mandshurica)、平榛(Cory-lus heterophylla)、红松(Pinus koraiensis)、樱桃(Cerasus pseudocerasus)5种具有不同特征的林木种子扩散的影响.结果表明:大林...     

Attosecond synchronization of high-harmonic soft x-rays

Subfemtosecond light pulses can be obtained by superposing several high harmonics of an intense laser pulse. Provided that the harmonics are emitted simultaneously, increasing their number should result in shorter pulses. However, we found that the high harmonics were not synchronized on an attosecond time scale, thus setting a lower limit to the achievable x-ray pulse duration. We showed that the synchronization could be improved considerably by controlling the underlying ultrafast electron dynamics, to provide pulses of 130 attoseconds in duration. We discuss the possibility of achieving even shorter pulses, which would allow us to track fast electron processes in matter.     

种薯大小对整薯播种马铃薯生长发育与产量的影响

对采用整薯播种的种薯大小对马铃薯生长发育与产量的影响进行研究的结果表明:在10～90g大小的种薯范围内,随种薯增大,马铃薯生物量呈递增趋势,种薯大于30g时,块茎产量明显提高,平均比使用30g以下的种薯增产8.64%～40.21%.但种薯越大,用种量越大,种薯成本也越高.从节本增效的角度分析,生产上应选用50～70g的种薯为宜.     

Effects of pulse shaping in laser spectroscopy and nuclear magnetic resonance

Pulsed excitation fields are routinely used in most laser and nuclear magnetic resonance (NMR) experiments. In the NMR case, constant amplitude (rectangular) pulses have traditionally been used; in laser spectroscopy the exact pulse shape is often unknown or changes from shot to shot. This article is an overview of the effects of radio-frequency and laser pulse shapes and the instrumental requirements for pulse shaping. NMR applications to selective excitation, solvent suppression, elimination of phase roll, and reduced power dissipation are discussed, as are optical applications to soliton generation, velocity selective excitation, and quantitative population transfer.     

樟子松优良采种林分划分方法的研究

本文将林木树种单株选优原则和方法运用到林木群体选择和划分上。注意林木单株的数量指标(生长量指标)和质量指标(形质指标)的结合;把对林木生长量有直接关系的形质指标,作为单株评价的一部分,考虑在单株选择之中,作为提高单株选优质量和准确性的根据。由此将林分树木划分为4级,再根据4级林木的比例而对林分进行分级。进而划分了种子林分,这对当前采种基地的划分和建立有着重要参考价值。     

兴安落叶松鞘蛾种群密度的自然调节及意义

鞘蛾种群数量不可能无限制增长,其原因是多方面因素综合作用的结果。风、食物、天敌及鞘蛾的自身密度等对鞘蛾的数量增长都有明显的抑制作用。春风能使树冠上27％左右的鞘蛾幼虫落地;早霜、晚霜、松毛虫、叶蜂及落叶松早期落叶病等都能直接影响鞘蛾食物的质量和数量,进而间接地使鞘蛾种群密度降低。捕食鞘蛾的天敌主要有鸟类、蚂蚁和蜘蛛;寄生性天敌多属于金小蜂科(Pteromalidae)、姬小蜂科(Eulophidae)、姬蜂科(Ichneumonidae)及茧蜂科(Braconidae)等。由鞘蛾自身密度所引起的自我调节是促使种群进化发展的重要因素之一,但是,这种因素的作用只有在密度大的时候方能显现出来。     

Impact of El Nino and logging on canopy tree recruitment in borneo

Dipterocarpaceae, the dominant family of Bornean canopy trees, display the unusual reproductive strategy of strict interspecific mast-fruiting. During 1986-99, more than 50 dipterocarp species dispersed seed only within a 1- to 2-month period every 3 to 4 years during El Nino-Southern Oscillation events. Synchronous seed production occurred across extensive areas and was essential for satiating seed predators. Logging of dipterocarps reduced the extent and intensity of these reproductive episodes and exacerbated local El Nino conditions. Viable seed and seedling establishment have declined as a result of climate, logging, and predators. Since 1991, dipterocarps have experienced recruitment failure within a national park, now surrounded by logged forest.     

吡虫啉悬浮种衣剂对玉米田节肢动物群落及主要非靶标害虫的影响

【目的】明确吡虫啉种衣剂对玉米田节肢动物群落及主要非靶标害虫的影响,为种衣剂的科学使用及玉米害虫防控提供理论依据。【方法】分别于2015年和2016年6—9月,在河南农业大学许昌校区试验田,设置600 g·L-1吡虫啉悬浮种衣剂推荐最高使用剂量及其2倍和4倍剂量进行种子包衣,以清水为对照,每个处理重复4次,随机区组排列。每小区采用5点取样方法,每点连续标记10株玉米,分别在玉米苗期、喇叭口期、孕穗期、灌浆初期和灌浆中期调查样点内玉米植株上全部节肢动物的种类及其数量,分析不同处理区节肢动物的群落特征。在玉米灌浆期,调查样点内玉米穗部害虫种类及数量;玉米成熟时每小区收获两行,每行连续收取50株,调查雌穗上和茎秆中的鳞翅目幼虫种类和数量,分析吡虫啉种衣剂对主要非靶标害虫的影响。【结果】种衣剂处理不影响玉米田节肢动物群落物种种类,处理区与对照区的物种丰富度随时间的变化趋势基本相似,同一时间内不同处理区物种丰富度的差异与有些物种的密度低而在调查样点内的分布不均匀有关。吡虫啉种衣剂处理不会造成玉米田节肢动物群落多样性和均匀度下降,在靶标害虫玉米蚜发生量大时还能通过抑制玉米蚜的数量而使多样性和均匀度增加。种衣剂处理对玉米田节肢动物优势种的影响不仅年份间有差异而且不同玉米生育期间也有差异,在靶标害虫玉米蚜种群数量较高的2015年,玉米生长前期种衣剂处理区的植食性昆虫和捕食性天敌优势种与空白对照区基本一致,灌浆期黏虫和草间小黑蛛分别成为种衣剂2倍和4倍剂量处理区的植食性昆虫和捕食性天敌的优势种;在玉米蚜种群数量较小的2016年,孕穗期以后亚洲玉米螟和棉铃虫为各处理区植食性昆虫优势种,龟纹瓢虫和异色瓢虫成为捕食性天敌优势种。玉米不同生育期各处理区优势种的优势度指标与其优势集中度指标变化趋势相似。种衣剂处理对穗部鳞翅目幼虫的影响程度较复杂,如玉米灌浆初期和灌浆中期种衣剂处理区亚洲玉米螟幼虫种群数量均高于或显著高于对照区;灌浆初期种衣剂处理区桃蛀螟幼虫种群数量均显著高于对照,灌浆中期则低于或显著低于对照;灌浆中期种衣剂处理区黏虫幼虫种群密度均高于对照;种衣剂处理区棉铃虫幼虫密度与对照区虽有不同,但差异不显著。综合两年的调查结果,玉米灌浆期种衣剂处理区亚洲玉米螟、桃蛀螟和黏虫幼虫种群密度有增加的现象,但其种群密度与600 g·L-1吡虫啉悬浮种衣剂处理剂量没有明显的相关性。【结论】建议吡虫啉种衣剂处理玉米田应注意防控鳞翅目穗部害虫。     

Biomass, size, and trophic status of top predators in the Pacific Ocean

Fisheries have removed at least 50 million tons of tuna and other top-level predators from the Pacific Ocean pelagic ecosystem since 1950, leading to concerns about a catastrophic reduction in population biomass and the collapse of oceanic food chains. We analyzed all available data from Pacific tuna fisheries for 1950-2004 to provide comprehensive estimates of fishery impacts on population biomass and size structure. Current biomass ranges among species from 36 to 91% of the biomass predicted in the absence of fishing, a level consistent with or higher than standard fisheries management targets. Fish larger than 175 centimeters fork length have decreased from 5% to approximately 1% of the total population. The trophic level of the catch has decreased slightly, but there is no detectable decrease in the trophic level of the population. These results indicate substantial, though not catastrophic, impacts of fisheries on these top-level predators and minor impacts on the ecosystem in the Pacific Ocean.     

腾冲红花油茶自然和人工种群种实性状变异研究

为了选择改良腾冲红花油茶的种实经济性状,对面积较大的3个天然种群和6个人工种群样株的12个种实性状和指标的变异进行了分析。结果显示:除果径在起源间无显著差异外,其余性状在起源间、起源内种群间及种群内单株间的变异均达到极显著水平,其方差分量为单株间起源内种源间起源间,不同性状相对变异程度有所不同。果实性状中果型与种子性状、产量性状呈显著或极显著负相关,其他性状与种子性状、产量性状呈显著或极显著正相关;种子性状与产量性状呈极显著正相关;果型、单果籽质量、出籽率、仁油率、籽油率及果油量是主要的遗传变异性状;果型、海拔与单位面积产油量呈显著负相关。提出了腾冲红花油茶群体和优株选择的主要指标和策略,为其可持续改良提供了科学依据。     

Ultrafast X-ray Pulses from Laser-Produced Plasmas

A high-temperature plasma is created when an intense laser pulse is focused onto the surface of a solid. An ultrafast pulse of x-ray radiation is emitted from such a plasma when the laser pulse length is less than a picosecond. A high-speed streak camera detector was used to determine the duration of these x-ray pulses, and computer simulations of the plasmas agree with the experimental results. Scaling laws predict that brighter and more efficient x-ray sources will be obtained by the use of more intense laser pulses. These sources can be used for time-resolved x-ray scattering studies and for the development of x-ray lasers.     

Periodical cicadas as resource pulses in North American forests

Resource pulses are occasional events of ephemeral resource superabundance that occur in many ecosystems. Aboveground consumers in diverse communities often respond strongly to resource pulses, but few studies have investigated the belowground consequences of resource pulses in natural ecosystems. This study shows that resource pulses of 17-year periodical cicadas (Magicicada spp.) directly increase microbial biomass and nitrogen availability in forest soils, with indirect effects on growth and reproduction in forest plants. These findings suggest that pulses of periodical cicadas create "bottom-up cascades," resulting in strong and reciprocal links between the aboveground and belowground components of a North American forest ecosystem.     

食物链长度远因与近因研究进展综述

食物链长度是生态系统的基本属性,其变化决定着群落结构和生态系统功能。稳定同位素分析技术的进步推进了生态系统中食物链长度决定因子相关研究的开展。尽管近期的研究证明了食物链长度与资源可利用性、生态系统大小、干扰等远因之间的关系,但是对于食物网内部结构变化这一近因对食物链长度的影响作用关注较少。综述了边界明确和开放类型淡水生态系统中食物链长度的相关研究进展;探讨了远因和近因机制在决定食物链长度中的作用;给出了判断不同层次和尺度上决定食物链长度机制的概念框架;为今后更好的开展不同生态系统间食物链长度的比较研究提出了建议。     

Dialects in elephatn seals

Threat vocalizations of male elephant seals Mirounga angustirostris vary among four populations on islands off the coast of California and Baja California, Mexico. Males at San Nicolas Island in Southern California emit sound pulses at more than double the rate of males at A?o Nuevo Island, 528 kilometers north. Mean pulse rates at San Miguel Island and Isla de Guadalupe (408 and 944 kilometers south of A?o Nuevo, respectively) are intermediate to these two. Pulse rate is homogeneous within each population and consistent in the same individual. Other properties of the calls which separate populations are pulse duration and embellishment of the initial or terminal pulse in a series. These geographical differences in vocal behavior resemble local dialects in birds and humans.     

连香树种子大小分布及其变异研究

研究了茂县山地生态系统定位研究站人工连香树种群个体种子大小分布及变异。结果表明,连香树种子大小分布呈正态分布,种子大小为(0.4±0.1)mg,其变化范围为0.1~1.2 mg;连香树个体间种子大小存在明显的差异,变异幅度较大,变异系数为31.8%;种子大小变异可能来源于个体间。     

Enhanced optical emission during Crab giant radio pulses

We detected a correlation between optical and giant radio pulse emission from the Crab pulsar. Optical pulses coincident with the giant radio pulses were on average 3% brighter than those coincident with normal radio pulses. Combined with the lack of any other pulse profile changes, this result indicates that both the giant radio pulses and the increased optical emission are linked to an increase in the electron-positron plasma density.     

Paleolithic population growth pulses evidenced by small animal exploitation

Variations in small game hunting along the northern and eastern rims of the Mediterranean Sea and results from predator-prey simulation modeling indicate that human population densities increased abruptly during the late Middle Paleolithic and again during the Upper and Epi-Paleolithic periods. The demographic pulses are evidenced by increasing reliance on agile, fast-reproducing partridges, hares, and rabbits at the expense of slow-reproducing but easily caught tortoises and marine shellfish and, concurrently, climate-independent size diminution in tortoises and shellfish. The results indicate that human populations of the early Middle Paleolithic were exceptionally small and highly dispersed.     

Pulse structure of four pulsars

The pulse structure of the four known pulsars is given. The pulse is about 38 milliseconds for the two pulsars of longest period, and within the pulsewidth three subpulses typically appear. The pulsar of next longest period typically radiates two pulses separated about 23 milliseconds in time. The one short-period pulsar emits single pulses of constant shape. The first subpulses of all pulsars have nearly the same shape. The shape of the first subpulse agrees well with the pulse shape expected from a radio-emitting sphere which is excited by a spherically expanding disturbance, and in which the radio emission, once excited, decays exponentially.