铅对草坪植物生物量与叶绿素水平的影响

通过盆载模拟试验研究了铅对植物生物量、叶片叶缘素含量变化的影响，以及植物中毒后的症状。结果表明，铅对植物根系生长发育影响极大，可使根冠细胞有丝分裂减少、根量减少。铅进入叶肉组织后导致叶片失绿，严重时使叶片枯黄死亡。试验早期植物中毒症状表现为根冠膨大变黑，严重时根系腐烂。当营养液中Pb浓度达5.0mol／m^3时，试验后期引起植物死亡且不易恢复。     

Response of forest soil properties to urbanization gradients in three metropolitan areas

We investigated the effects of urban environments on the chemical properties of forest soils in the metropolitan areas of Baltimore, New York, and Budapest. We hypothesized that soils in forest patches in each city will exhibit changes in chemistry corresponding to urbanization gradients, but more strongly with various urban metrics than distance to the urban core. Moreover, differences in parent material and development patterns would differentially affect the soil chemical response in each metropolitan area. Results showed that soil chemical properties varied with measures of urban land use in all three cities, including distance to the urban core, which was an unexpected result. Moreover, the results showed that the spatial extent and amount of change was greater in New York than in Baltimore and Budapest for those elements that showed a relationship to the urbanization gradient (Pb, Cu, and to a lesser extent Ca). The spatial relationship of the soil chemical properties to distance varied from city to city. In New York, concentrations of Pb, Cu, and Ca decreased to approximately background concentrations at 75 km from the urban core. By contrast, concentrations of these elements decreased closer to the urban core in Baltimore and Budapest. Moreover, a threshold was reached at about 75% urban land use above which concentrations of Pb and Cu increased by more than twofold relative to concentrations below this threshold. Results of this study suggest that forest soils are responding to urbanization gradients in all three cities, though characteristics of each city (spatial pattern of development, parent material, and pollution sources) influenced the soil chemical response.     

Grouping strategies and lead factors for ration formulation in milking ewes of the Chios breed

The aim of this study was to develop an efficient strategy for ration formulation for milking ewes of the Chios breed in Greece. The strategy involved two and three groupings according to production level and challenge feeding using lead factors. Lead factors, that adjust upwards the average production of a flock or a group of ewes, were calculated for the 83rd and the 90th percentile, using 49,237 milk test-day records from 549 flock-test-days, referring to 64 flocks and 97 complete lactations. Lead factors were 1.25 for the single-group, 1.14 and 1.17 for the two-group, and 1.11, 1.07 and 1.15 for the three-group strategy for the 83rd percentile. Regarding the 90th percentile, these were: 1.33 for the single-group, 1.18 and 1.19 for the two-group, and 1.15, 1.09 and 1.16 for the three-group strategy. Analysis of variance was used to assess the influence of several effects on lead factors. Flock-year and mean and standard deviation milk yield were significant (P < 0.05) in nearly all cases, leading to calculation of different lead factors for high (> 250 kg of milk/ewe/year) and low (< 250 kg of milk/ewe/year) producing flocks. Higher producing flocks were associated with somewhat lower than average lead factors, while the opposite was true for lower producing flocks. In order to allow the sufficient expression of the genetic potential of the best ewes and accurately estimate their genetic value under Greek conditions, the 90th percentile strategy can be adopted for the higher producing groups and the 83rd for the lower ones.     

Dual Chamber Pacemaker Implantation in Dogs with Atrioventricular Block

Background: Pacemaker implantation is the treatment of choice for symptomatic bradyarrhythmias. In dogs, a single chamber system is commonly used. In human patients with high-grade 2nd- or 3rd-degree atrioventricular (AV) block, physiologic pacing is recommended, because it improves cardiac output, blood pressure, exercise tolerance, and quality of life. In dogs, this type of pacing is seldom used.
Hypothesis: The implantation of a dual chamber pacemaker in dogs with AV block is a feasible procedure for restoring AV synchrony.
Animals: Thirty-three privately owned dogs with high-grade 2nd- or 3rd-degree AV block were included.
Methods: Patient data of all dogs with AV block presented for pacemaker implantation between December 1997 and November 2004 were reviewed.
Results: Dual chamber pacemaker implantation with AV synchronous stimulation was successfully performed in 33/33 dogs (100%). In 9/33 (27%) major and in 12/33 (36%) minor complications were observed. Mean survival time for the patients discharged from hospital (n = 32) was 33.6 ± 20.4 months (range, 3.9–83.5 months).
Conclusion and Clinical Importance: Dual chamber pacing is a feasible procedure in dogs with 2nd- or 3rd-degree AV block and is not associated with a higher complication rate compared with single chamber pacemaker systems. A major advantage over ventricular demand pacemaker systems is the restoration of AV synchrony for a substantial period of time.     

铅胁迫对4种木本植物酶保护系统的影响

随着工业化、城市化进程的加速，城市铅污染日益严峻。通过植物酶保护系统对铅胁迫的响应研究，可以有效缓解城市铅污染问题。为此，本实验以红檀木（Loropetalum chinese（R．Rr．）Oliv．）、侧柏（Platycladus orientalis（L．）End]1）、金合欢（Acacia famesiana（Linn．）Wind）、杨树（Populusdeltoides×Populus nigara）为材料，采用盆栽试验，分别设置CK（不加Pb）、T1（300mg·kg-1，干土）、T2（450mg·kg-1干土）、T3（600mg·kg-1干土）4个Pb处理浓度，研究了4树种酶保护系统对铅胁迫的响应机理。在铅胁迫下，各树种SOD、POD活性变化显著（P〈0．05），杨树、侧柏、红檀木的POD、SOD均高于对照，其中又以杨树的SOD、POD活性最高，分别为800U·g-1，103U·g-1·min-1，金合欢的酶活性在处理浓度超过300mg·kg-1，后迅速降低。CAT活性在杨树中显著上升（P〈0．05），侧柏中的CAT活性未发生显著变化，金合欢、红檀木中的CAT活性则显著下降（P〈0．05）。木本植物酶保护系统对铅胁迫的响应存在显著的种间差异，其抗铅污染能力依次表现为杨树〉红檀木〉侧柏〉金合欢。     

北京地区城乡街尘中铅污染分异特征研究

城乡环境背景与管理的显著差异,对街尘污染的影响日益突显。通过对北京中心城区、卫星城区、乡镇、村庄以及中心城区中的城中村共162个点位的街尘颗粒物与Pb浓度调查和分析,结果表明:城乡之间街尘中颗粒分布及其Pb含量存在较大差异。其中,中心城区以及卫星城区的街尘中Pb浓度显著高于村庄,而单位面积的Pb质量低于缺乏管理的城中村和村庄;街尘中颗粒物在各粒径段浓度总体存在着城区高于村庄的现象,且研究区域存在街尘中颗粒物随着粒径的减小Pb浓度增加的趋势,但大于150μm的颗粒物浓度波动较大;城市道路的细粒径污染负荷贡献率高于村庄道路,细粒径的污染负荷贡献率存在"溢价现象",而粗粒径则反之。研究结果建议对街尘污染控制应城乡并重,因地适宜,并特别关注街尘的粒径效应所带来的影响。     

铅胁迫对金盏银盘生长及生理生化的影响

通过水培模拟试验,研究不同处理时间和不同浓度铅胁迫下金盏银盘生物量及生理生化指标。结果表明,低浓度铅对金盏银盘生长有促进、高浓度有抑制作用;低浓度铅处理(Pb2+≤20 mg/L)对叶绿素合成有促进、高浓度抑制作用,而随处理时间的延长,各处理浓度最终均引起叶绿素含量的下降;在铅胁迫处理2~8 d内,各浓度处理脯氨酸含量都高于对照,在处理10~12 d内,低浓度铅处理(Pb2+≤10 mg/L)脯氨酸含量高于对照,随处理时间的延长变化不规律;在铅胁迫12 d内,丙二醛含量基本均随着铅浓度的升高而增加,且均高于对照,随时间增加表现为先升高后降低再升高的趋势;在铅处理8 d内,POD活性随着铅浓度的增加基本表现为先升高后降低再升高的趋势,而在处理8 d后,基本表现为先降低后升高的趋势;铅胁迫对SOD活性有一定抑制作用,各铅浓度处理在相同处理时间对SOD活性的抑制无明显的规律。POD活性波动较大,而SOD活性最终都会增加。     

教师应当成为学生坚固的"防火墙"

本文从实际出发,探讨了教师应如何引导学生充分利用网络资源进行学习,同时远离“网毒”的侵噬。     

Improved line weighting reduces seabird bycatch without affecting fish catch in the Brazilian pelagic longline fishery

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