连作、迎茬和轮作大豆对田间杂草群落变化的影响

采用定位试验方法研究了大豆长期(10—13年)连作、豆麦豆迎茬、豆米豆迎茬、麦米豆轮作、麦豆豆和麦豆豆豆短期连作条件下大豆田杂草密度、杂草种群和杂草地上鲜重变化。试验结果表明：田间杂草密度以豆麦豆迎茬最大，且明显高于其它茬口，豆米豆迎茬田间杂草密度最小，杂草密度在不同年际间存在着差异；北方大豆田杂草主要有藜、鸭趾草、苋、稗、龙葵、野苏、卷茎蓼、鬼针等；藜、鸭趾草、苋、稗为所有茬口所共有；随着连作年限的增加，使连作区一些杂草种类增加，这种差别主要是在双子叶杂草之间，单子叶杂草种类没有变化；豆麦豆迎茬田间杂草鲜重最大，但干旱年份各茬口杂草鲜重普遍减少。     

2个玉米优势群体穗粒性状的密度效应分析

对Reid和非Reid 2个玉米优势群体在2种密度条件下6个穗粒性状的分析结果表明,各穗粒性状都是由多基因控制的复杂数量性状;高密度使除非Reid群体穗粗外的其余性状变劣,使非Reid群体的百粒重外的其余各性状的变异系数增大,高密度更有利于对性状实施表型选择,穗粒重和穗长更适宜作为穗粒性状耐密性的选择指标;Reid群体的耐密性优于非Reid群体;穗粒重同时由多个穗粒性状所决定,在利用Reid群体进行自交系选育过程中,更应注重协调各穗粒性状间的关系。     

重要林木害虫松幽天牛危害特点的研究

文章简要报道了松幽天牛Asemum amurenseKraatz在河北丰宁的发生和危害状况,讨论了该虫成灾的主要原因,并提出防治建议和对策。该虫在河北丰宁造成的灾害十分严重,主要危害油松,成灾区有虫株率50%以上,虫口密度126头/株;造成严重危害的主要原因是油松生存环境恶劣,连续干旱,对该虫生物生态学特性缺乏了解以及缺少有效监控技术。     

Analysis and comparison on population dynamics betweenAdenophora lobophylla andAdenophora potaninii by leslie matrix

The population dynamic tendency ofAdenophora lobophylla Hong as an endangered species andAdenophora potaninii Korsh as widespread species, has been predicted by the Leslie matrix. And the comparison and analysis on the age structures between two species have been carried out in this paper. The results demonstrate theA. lobophylla populations which have the reasonable age structures perform slowly negative or positive increment at altitude 2300–3400 m. Especially. below altitude 2700 m. there are many populations performing seriously declining tendency. Contrary.A potaninii populations could adapt to environment perfectly at the corresponding condition without finding the population which performs the seriously declining tendency. The differences in developing tendency of population between the two species demonstrate thatA. lobophylla populations have the weaker ability to adapt to the external unfavorable conditions. The project was supported by Chinese Natural Science Foundation. (No. 3939150) The experiment carried out at the Botanical Department of University Federal Sao Carols in Brazil (Responsible Editor: Zhu Hong)     

论居群观念与花卉分类的关系

该文对居群观念的产生与发展及其对传统植物分类学所带来的影响进行了简要的回顾与分析．以蜡梅属（Ｃｈｉｍｏｎａｎｔｈｕｓ）等花卉植物为例,从居群观念与花卉植物种、品种的形态分类,以及与花粉粒微观形态、同工酶、ＤＮＡ分析等研究手段的关系进行了全方位的探讨,指出了我国花卉植物在系统与进化植物学研究领域存在的主要问题     

福建寿宁县兽害猖獗的成因及对策初探

1998～2006年,以寿宁县为调查对象,运用机械抽样法调查样带69条,运用访问调查法调查猎户农户100余户,运用点面互换法调查全县范围内农田作物受害程度。结果表明,全县近半数的村,15%的耕地存在兽害,99%的兽害及其损失源于野猪的活动。分析表明,兽害的成因有种群爆发、物种灭绝和生态系统衰败诸多因素,而人为干扰是各种现象的起因。最后提出治理山区兽害的对策,尤其应加强生态系统恢复和自然保护区建设。     

人口城镇化与土地城镇化协调关系实证分析--以湖北省为例

选取湖北省为研究对象,在深入理解城镇化内涵的基础上,分别构建了人口城镇化与土地城镇化评价指标体系,运用SPSS17．0统计分析软件的主成分分析法确定了各指标权重值,并分别计算了湖北省1995～2012年的人口城镇化指数与土地城镇化指数,利用协调度模型逐年计算了湖北省人口城镇化与土地城镇化协调度,比照协调类型评价标准,揭示了湖北省人口城镇化与土地城镇化协调发展的时间演变特征及趋势。     

Genetic structure of the migratory catfish Pseudoplatystoma corruscans (Siluriformes: Pimelodidae) suggests homing behaviour

Abstract –  Pseudoplatystoma corruscans is distributed widely in the La Plata Basin in Brazil, where it is a very important species because of its high commercial value and ecological role as a voracious predator. This species undertakes long migrations during the dry and rainy seasons to feed and reproduce, respectively. In this study, we analysed seven microsatellite loci to test the hypotheses of the existence of a single panmictic population of P. corruscans in the La Plata Basin. All microsatellites analysed were highly polymorphic with the number of alleles per locus ranging from seven (Pcor28) to 30 (Pcor10). Across all samples, 107 alleles were detected. Thirty alleles were private, i.e., found in only one sample. Highly significant genetic differentiation was observed among samples in three of the four analyses performed: F _ST (from 0.03435 to 0.16349, P  < 0.05), Analysis of molecular variance (amova) F _ST = 8.25% ( P  < 0.0001) and amova R _ST = 9.72% ( P  < 0.0001). A microsatellite multilocus Bayesian assignment test with the programme structure confirmed the division of the fishes into six groups largely concurrent with main branches on a population neighbour-joining tree. The obtained results rejected the panmixia hypothesis. On the other hand, the documented long-distance movements of P. corruscans and the geographical scale of genetic differentiation found in this study indicate a strong tendency for fish of this species to utilise their natal nursery regions for reproduction, which represents the first demonstrated example of homing in a freshwater catfish in South America.     

Influences of human activity and climate on the stock-recruitment dynamics of whitefish, Coregonus lavaretus, in Lake Geneva

Abstract  Analysis of long-term catches from the deep peri-alpine Lake Geneva, showed a shift in the stock-recruitment relationship of Coregonus lavaretus (L.), a target species of commercial fishing. This change was mainly related to large-scale meteorological factors. Higher spring water temperatures may have improved larval survival and hence recruitment of whitefish via: (1) a better match between the hatching date of whitefish larvae and development of their zooplankton prey; and (2) the positive temperature effect on larval growth. In Lake Geneva, changes in regulatory mechanisms coupled with stocking and improved water-quality have led to an explosion in the C. lavaretus population in recent years. These results highlight the relevance of long-term changes in the stock-recruitment relationship for management of aquatic ecosystems that are sensitive to climate forcing.     

Evaluation of the intrinsic competitiveness and saprophytic competence of Rhizobium tropici IIB strains

Inoculation of beans (Phaseolus vulgaris L.) with strains of R. tropici IIB and R. etli resulted in the disappearance of the R. tropici IIB stains from the nodule population and their replacement by other (non R. tropici IIB) bean symbionts (Vlassak et al. 1996). Coinoculation studies in monoxenic conditions and in soil core microcosms with plants harvested at two different growth stages indicated that the inoculated R. tropici IIB strains CIAT899 and F98.5 possess a good intrinsic competitiveness which declines, however, at a later plant growth stage and in soil conditions. The poor saprophytic competence of R. tropici IIB strain CIAT899 was further demonstrated by its poor survival in soil core microcosms after bean harvest. Strains were isolated from the field plots with a 3-year bean-planting history, characterized and evaluated for their competitiveness against R. tropici IIB strain CIAT899. Isolates from field plots, which had been repeatedly inoculated with R. tropici IIB strain CIAT899, showed a higher nodule occupancy compared to R. tropici IIB strain CIAT899, and this higher competitiveness exhibited by the field isolates might be an additional reason for the poor performance of R. tropici IIB strain CIAT899 in the field study. Plots with and without a history of bean production revealed after 3-year bean cultivation an almost totally different population that also significantly differed in competitiveness. Received: 12 February 1996