How Kentish plovers,<Emphasis Type="Italic"> Charadrius alexandrinus</Emphasis>, cope with heat stress during incubation

Biparental incubation is frequent among shorebirds and is expected when the survival prospects of offspring increase relative to uniparental incubation. To understand why this occurs, it is important to identify the factors that constrain uniparental incubation. It is assumed that birds choose nesting sites that provide an appropriate microclimate for incubation. Many shorebirds nest in sites with no or little cover, where ambient temperatures at ground level might be >50°C during very hot days. Shorebirds nest in exposed sites because predation risk on incubating adults is higher in covered sites. In hot environments, incubating shorebirds might experience heat stress in exposed sites, and this may compromise nesting success if adults are unable to attend their nests continuously, limiting the possibilities of uniparental incubation and thus the expression of a sexual conflict over incubation. The operative temperatures of Kentish plovers (Charadrius alexandrinus) were recorded in exposed and covered sites, and the thermal behaviour and incubating tactics of pair members were studied in a hot environment. During the hottest part of the day, there was a difference of 10–15°C in the operative temperatures of plovers between covered and exposed sites. Plovers in covered sites did not exhibit any thermoregulatory behaviour indicative of thermal stress, probably because the thermal range encountered by them in such places during most of the daytime was close to the thermo-neutral zone. The frequency with which plovers in exposed sites exhibited thermoregulatory behaviour was related to ambient temperature. Under very hot conditions, incubating birds were probably unable to maintain homeostasis for long periods and pair members resorted to shortening incubation bouts. Female Kentish plovers mainly incubate in the daytime and males during the night. However, the probability of diurnal incubation by males increased with ambient temperature in exposed nests, but not in covered ones. In fact, the frequency of participation in diurnal incubation by males was greater in exposed than in covered sites, suggesting that the participation of males in diurnal incubation may be related to the inability of females to stay at the nest during long periods when the ambient temperature is high. Even after resorting to shortened incubation bouts, the plovers may be unable to attend their nests continuously during heat waves, and the nests may be deserted. The propensity of plovers to desert their nests was affected by proximity to water, with nests located close to water being deserted less frequently. It seems likely that susceptibility to thermal stress changed in relation to proximity to water because in sites close to water it was possible to belly-soak, which would allow a more continuous nest attendance. Therefore, despite the adoption of behavioural solutions to face heavy heat loads, nesting success was vulnerable to these solutions because heat stress during extended periods may constrain parental nest attendance, and this may limit the opportunities for sexual conflicts over incubation.Communicated by J. Graves     

五氯酚对鲫鱼肝脏的氧化损伤

将鲫鱼暴露于浓度分别为 0 .0 0 16、0 .0 16、0 .16mg·L-1的PCP溶液 15d ,同时做空白对照 ,测定鲫鱼肝脏的SOD、GSH、MDA以及NO、NOS等指标。试验结果表明 ,0 .16mg·L-1组处理的鲫鱼第 13天全部死亡。与对照相比 ,在 0 .0 0 16mg·L-1浓度下 ,PCP提高了鲫鱼肝脏MDA和NO含量 ,GSH含量降低 ,SOD活性被抑制 ,NOS活性有所升高。在 0 .0 16mg·L-1浓度组 ,PCP对几个指标的影响比 0 0 0 16mg·L-1组大 ,与对照相比 ,具有显著差异 ,说明PCP暴露可导致鲫鱼肝脏的氧化损伤     

茉莉酸甲酯(MeJA)对水稻幼苗的抗旱生理效应

茉莉酸类物质(Jas)是植物体内广泛存在的生长调节物质,它作为内源信号分子参与植物在机械伤害、病虫害、干旱、盐胁迫、低温等条件下的抗逆反应。选用抗旱性存在明显差异的两个水稻(Oryza sativa L.)品种中二欧六和丰华占作为实验材料,通过设置对照、干旱、干旱 茉莉酸甲酯(MeJA)三种处理研究了茉莉酸甲酯对水稻幼苗的抗旱生理效应。研究结果表明,干旱胁迫后两个水稻品种幼苗叶片水势均显著降低,而干旱后喷施茉莉酸甲酯能明显增加叶片的水势,改善叶片的水分状况,抗旱性强的品种水势增加幅度较大。干旱胁迫后水稻叶片的抗氧化酶活性,包括超氧化物歧化酶(SOD)、过氧化物酶(POD)及过氧化氢酶(CAT)和有机渗透调节物质,包括可溶性糖、脯氨酸及游离氨基酸含量均大幅度上升,而干旱 茉莉酸甲酯处理则能降低了这些物质的含量,两个水稻品种的变化趋势表现一致。研究结果表明外施茉莉酸甲酯在一定程度上能减缓干旱胁迫对水稻幼苗造成的伤害,有效地提高抗旱性,但这这种增强效应在不同水稻品种间存在一定差异。     

浅谈会计职业判断

随着我国市场经济的发展以及会计准则的日趋完善,会计职业判断在会计工作中的地位变得越来越重要.但是,在我国目前的实际会计工作中,很多问题却影响了会计职业判断作用的发挥.因此,本文主要分析了会计职业判断过程中存在的问题,并针对这些问题提出了相应的对策和建议.     

广东省洪水资源化探讨

广东省多年平均人海水量4018亿m^2，并主要集中在汛期以洪水形式流人大海。文章根据广东省水资源与洪水特点，探讨了洪水资源化的途径及其安全保障措施：利用现有和新建水工程，采用科学合理的蓄、引、提、回灌与冲污等方式使洪水资源化；加强防洪调度与管理，以降低洪水资源化风险，确保安全利用洪水。该研究对解决广东省目前部分地区资源性和水质性缺水具有重要意义。     

Environmental Impact of Undular Tidal Bores in Tropical Rivers

A tidal bore impacts significantly on the estuarine ecosystem, although little is known on the flow field, mixing and sediment motion beneath tidal bores. In the absence of detailed systematic field measurements, a quasi-steady flow analogy was applied to investigate undular tidal bores with inflow Froude numbers between 1.25 and 1.6. Experimental results indicated that rapid flow redistributions occur beneath the free-surface undulations, with significant variations in bed shear stress between wave crests and troughs. Dynamic similarity was used to predict detailed flow characteristics of undular tidal bores. The effects of periodic loading on river sediments, scour of river bed and flow mixing behind the bore are discussed. A better understanding of these processes will contribute to better management practices in tidal bore affected rivers, including the Styx and Daly rivers in tropical Australia.     

Estimation of the surface stress from the streamwise pressure gradient: The Kármán Integral Momentum Equation revisited

A method is developed to estimate the stress at the surface in a portable wind tunnel for wind erosion studies. The boundary layer height and the pressure gradient are used in a simple expression from the Kármán Integral Momentum Equation. Values of friction velocity u _* are within 10% of experimental values obtained through correlation techniques, including measurements of differential pressures with the Murdoch Turbulence Probe MTP and the X-wire, hot-wire anemometer XWA. Wind velocity and stress profiles reveal logarithmic trends and a constant stress layer near the surface in the DAWA portable wind tunnel. Realignment of the statistics with the mean wind is essential.     

干热河谷主要造林树种光合作用光抑制的防御机制

比较研究了干热河谷8个造林树种气孔导度、光合色素、叶绿索荧光的日变化和季节变化，结果表明：①气孔导度雨季较高，多呈“午睡”现象的双峰曲线日进程，旱季气孔导度很低，全呈单峰曲线日进程；叶绿素荧光动力学参数Fv／Fm呈反正态分布曲线日进程，qP和φPsⅡ呈正态分布曲线日进程，白昼qNP随时间呈上升趋势，表明树种启动了过剩激发能耗散功能．②叶绿素总含量、叶绿素a／b值及类胡萝卜素／叶绿素值从雨季到旱季都呈下降趋势，减少了对光能的吸收．③旱季马占相思(Acacia mangium)、刺槐(Robinia pseudoacacia)的Fv／Fm值明显低于雨季值，差异显著，发生了严重的光抑制；qP和qNP值除赤桉(Eucalyptus dulebsis)变化不明显外，其余树种旱季qP值下降而qNP值上升．④对干旱、高光强、高温光保护的主动适应方式是保持较高的光化学猝灭、PSII线性电子传递效率和维持一定耗散过剩光能的能力，如降低光化学猝灭而增加非光化学猝灭来适应逆境，则是一种对生长不利的内损耗被动适应方式．图4表2参14     

薄壁管无芯推压缩径过程的应力应变分析

薄壁管无芯推压缩径成形过程比薄壁管拉拔成形过程复杂得多,迄今很少有这方面的文献报道。本文首次根据主应力法,比较详细地推导了薄壁管无芯推压过程的应力分布和壁厚变化的计算公式,并给出了计算实例。     

辽宁浑河断裂带及其邻近地区水系格局构造节理与构造应力场的研究

本文根据浑河断裂带及其邻近地区的水系格局、构造节理和地震震源机制解等资料研究该区新构造时期以来的构造应力场。本区在同一地质构造作用下,构造应力场相同,为NEE向。浑河断裂以抚顺市石门岭煤矿区为界,断裂的东南段最新活动时期为261.95±26.05ka.B.P,为中更新世活动断裂,而东北段断裂的最新活动时期为44.7±3.6ka.B.P,表明晚更新世以来仍有活动。在NEE向构造应力场的作用下,北东向的浑河断裂反映为右旋逆冲的运动性质。