青海保护性耕作农田杂草群落组成及生物多样性

采用倒置“W”9点取样法对青海保护性耕作农田杂草种类进行了调查,以明确田间杂草的种类组成及群落结构.结果表明,青海省保护性耕作农田杂草有67种,隶属于25科,其中优势杂草有密花香薷(Elsholtzia densa Benth)、猪殃殃(Galium maborasense Masamune)、野燕麦(Avena fatua Linn.)、藜(Chenopodium album L.)、苣荬菜(Sonhus arvensis Linn.)、大刺儿菜(Cephalanoplos setosum(Willd.) Kitam.)6种,是构成青海各地区保护性耕作农田杂草群落的主要优势种,区域性优势杂草有5种,常见杂草有17种,一般杂草有39种.湟中地区主要形成猪殃殃+密花香薷+藜+野燕麦+大刺儿菜+芦苇+尼泊尔蓼为主的杂草群落;民和地区为狗尾草+藜+扁蓄+野燕麦+田旋花+荞麦蔓+大刺儿菜,平安地区为野燕麦+猪殃殃+苣荬菜+大刺儿菜+赖草+荞麦蔓+密花香薷+扁蓄+泽漆,化隆地区为薄蒴草+猪殃殃+野燕麦+荞麦蔓+苣荬菜+密花香薷,大通地区为野燕麦+猪殃殃+藜+大刺儿菜+问荆+密花香薷,刚察地区为密花香薷+西伯利亚蓼+薄蒴草+藜+微孔草+旱雀麦+苣荬菜+野胡萝卜.湟中和大通地区保护性耕作农田杂草群落的物种丰富度、多样性及均匀度较其它地区高,而优势度较低.从群落相似性来看,湟中和大通群落结构最为相似.地理环境、气候条件及控草措施的不同,可能是导致保护性耕作农田杂草发生及群落组成产生差异的原因.     

Development of arable weed seedbanks during the 6 years after the change from conventional to organic farming

All of the arable land of a farm in southern Germany was investigated during an 8-year period, starting 2 years before and ending 6 years after the change to organic farming. The first 3 years after the conversion, the total seed number in the soil increased from 4050 to 17 320 m⁻². From the fourth to the sixth year, it dropped back to 10 220 m⁻². The number of seeds increased particularly at sites with a low crop cover and a high density of weed plants at the soil surface. The increase predominantly occurring on the more fertile soils may have been caused by the rotation commencing with less competitive crops. Crops which increased the seedbank by 30–40% were winter cereals, sunflowers and lupins. Potatoes and sown fallow caused no significant change and grass–clover mixtures even reduced the number of seeds by 39%. Among 44 species occurring frequently enough for statistical analysis, 31 increased and only 3 decreased. The change of management particularly increased summer annual, perennial and dicotyledonous weeds. This can be attributed to both operations which are characteristic of organic farming (e.g. replacing herbicide applications by mechanical weed control) and to general modifications of the management practice which may also occur in non-organic farming systems (increasing the percentage of broad leaved and spring sown crops in crop rotation). The present study confirms investigations into the aboveground vegetation that indicate that arable organic farming favours plant species diversity and provides evidence that the conversion need not encourage the dominance of a few noxious weeds.     

Influence of reward level on vertical distribution and growthof rainbow trout Oncorhynchus mykiss fed on demand with self-feeders

ABSTRACT:   The influence of reward level on vertical distribution and growthwas examined in rainbow trout fed on demand with self-feeders. Groupsof 15 trout with initial body weight of 140 g were maintainedat 14°C and feed access was restricted to a 12-h photophase.The trout received three reward levels with triplicates: 0.051 (low),0.089 (medium) and 0.267 g/kg fish/triggeractuation (high). Vertical distribution in the higher reward groupswas generally more even than that in the lower-reward groups, butthe behavioral characteristics of some individuals in a group couldplay an important role in determining vertical distribution. Moreover,no fish including the individuals responsible for trigger actuation,occupied the vicinity of a trigger. The small groups of 15 troutreceiving the medium-reward level obtained as much feed and grewas fast as the high-reward groups, but this was not the case forthe low-reward groups.     

沙拐枣群落特征与生态学特性的研究

本文通过定量定性分析，对沙拐枣群落的组成成分及种的多样性、群落的外貌特征、垂直结构、分布格局和种间联结以及群落的演替等方面进行了研究，结果表明：沙拐枣群落Ｓｈａｎｎｏｎ－Ｗｉｅｎｅｒ指数为２．５１９７、均匀度为０．８００４，个体密度为８．８９株／１００ｍ￣２，群落盖度约１％；沙拐枣种群王泊松分布，天然更新能力强，呈入侵状态；群落演替表现为初期种的多样性较高而向顶极方向趋于减少；并根据群落密度提出了治沙栽植密度为７４－１１１株／亩和封沙育草中对沙拐枣群落的利用途径。     

番茄多茸毛基因Ln的遗传研究

研究番茄多茸毛基因Ln的遗传模式，按孟德尔质量性状遗传研究设计，以栽培番茄多茸毛品系LS1369与普通品系强力62配制的六世代遗传研究群体，研究番茄多茸毛形态突变基因Ln的遗传机理，通过研究分析各世代的表现型和基因型的关系，提出控制多茸毛性状的Ln基因为单基因不完全显性遗传模式。     

Vertical distributions of two herbivorous cichlid fishes of the genus Tropheus in Lake Tanganyika, Africa

The vertical distributions of two herbivorous cichlid fishes, Tropheus moorii and Tropheus duboisi, were studied on the rocky slope at Luhanga and Bemba, 12 km apart, in Lake Tanganyika, Zaire, Africa. At Luhanga, where T duboisi were not present, T. moorii ranged from the shoreline to a site 30 m deep. At Bemba, T moorii occupied areas less than 18 m and T duboisi areas between 5 and 30 m. In the overlapping zone, 5–18 m depth, each fish held an intra- and interspecific feeding territory, involving size-dependent dominance relationship between neighbors irrespective of species. We indicate that the vertical distributions of these species are restricted by competitive interactions.     

Changes in landscape patterns in Georgia,USA

The objectives of this study were to determine how landscape patterns in Georgia, USA have changed through time and whether the spatial patterns varied by physiographic region. Historical aerial photography was used to analyze spatial patterns of land use from the 1930's to the 1980's. Land use patterns were quantified by: (1) mean number and size of patches; (2) fractal dimension of patches; (3) amount of edge between land uses; and (4) indices of diversity, dominance, and contagion. Forest cover increased in aerial extent and in mean patch size. The mean size of agricultural patches increased in the coastal plain and decreased in the mountains and piedmont. Edges between land uses decreased through time, indicating less dissection of the landscape. Fractal dimensions also decreased, indicating simpler patch shapes. Indices of diversity and dominance differed through time but not among regions; the contagion index differed among regions but not through time. A geographic trend of decreasing diversity and increasing dominance and contagion was observed from the mountains to the lower coastal plain. Landscape patterns exhibited the greatest changes in the piedmont region. Overall, the Georgia landscape has become less fragmented and more connected during the past 50 years. Changing patterns in the landscape may have implications for many ecological processes and resources.     

植物干细胞研究进展

该研究从植物干细胞的概念、茎端分生组织与根端分生组织特征及其各自调控的分子基础等方面综述了当前植物干细胞研究的新进展,同时,阐述了植物干细胞发生与分化受到内源性信号和外源性信号的共同调节,分析了内源基因以及外源调控分子的相互作用,并对植物干细胞的研究进行了展望。     

Magnetic resonance imaging of the ligamentous structures of the occipitoatlantoaxial region in the dog

Our objectives were to establish a magnetic resonance (MR) protocol for the examination of, and then describe, the normal ligaments and the supporting structures of the occipitoatlantoaxial region. This was done in 10 cadaver dogs. In addition, MR images of three patients with cervical pain localized to the occipitoatlantoaxial region are included to provide examples of ligamentous abnormalities. All ligaments were hypointense in all pulse sequences. The apical, dorsal atlantoaxial, and dorsal longitudinal vertebral ligaments were seen best in the sagittal T1W and PD-weighted images. The transverse ligament was best visualized in the transverse plane in all pulse sequences and appeared to be confluent with the dorsal longitudinal vertebral ligament dorsal to the dens in the sagittal plane. A 20° dorsal plane reconstructed image in 0.6-mm slice thickness was necessary to visualize the alar ligaments, which were visible in 9/10 dogs. The dorsal longitudinal vertebral ligament appeared continuous with the apical ligament and tectorial membrane. Abnormalities in clinically affected dogs included thickening of the alar ligaments, absence of transverse ligament and elongation, and irregularity of the apical ligament.     

Observations on the attachment of a piscine gill parasitic ergasilid (Crustacea: Copepoda)

The attachment of the piscine gill parasite, Ergasilus mirabilis Oldewage & van As, 1987 is described by means of scanning electron microscopy and light microscopy. A variety of sensory structures occur on and around the host contact surface of the parasite and proliferation of gill tissue occurs at the site of attachment. It would appear that this proliferation of host tissue results from the feeding behaviour of the parasite rather than the actual attachment thereof.