农业生产的生态管理

一、引言自50年代起,我国开始从传统农业向现代常规农业转变。随着这一转变的深化,农业生产力水平有了迅速的提高。然而,迅速增长的人口压力,使我国农业一直面临着一些严峻的问题。众多的人口,使我国人均自然资源占有量处于极低的水平。土地资源、水资源及矿产资源的短缺,已成为我国农业发展的基本限制     

松嫩平原羊草草场中羊草枯枝落叶形成过程的初步研究

枯枝落叶是草原生态系统中净第一性产量的一个重要组成部分。植物光合作用的产物,其中大部分以枯枝落叶的形式贮存在地面,是一个巨大的物质库。它对调节物质循环,维持草原生态平衡起着重要的作用。另一方     

Sun-compass orientation in the characidCheirodon pulcher

Synopsis Small microcharacidsCheirodon pulcher were netted during the dry season in pools of the savanna llanos at a considerable distance from the main river channel. Fish could have moved from the river to these pools using sun-compass orientation. Orientation responses of these fish were tested in a four-armed experimental device, exposed to direct sunlight or to azimuth-inverted sunlight reflected by a mirror. Groups of 20 fish were placed in a central area, released and then counted in the arm traps. When exposed to direct sunlight, fish oriented south, both in the morning and afternoon. Nevertheless, when the sun azimuth was inverted they oriented north, indicating that they use a sun-compass and that they compensate for sun-azimuth inversion at noon in a way that geographic headings remain constant throughout the day. These results reinforce previous laboratory interpretations which suggested that these flood plain species migrate inland during the high-water period and return to the main river channels before the dry season begins.     

Découverte d’une nouvelle faune d’âge cénomanien dans la région de Forthassa (Atlas saharien occidental,Algérie) : Implications biostratigraphiques et paléoenvironnementales

The upper Cretaceous of the eastern part of the Ksour Mountains (Western Saharan Atlas, Algeria) is classically subdivided into three fossiliferous lithostratigraphic formations: El Rhelida (lower Cenomanian), Mdaouer (lower-middle Cenomanian) and Rhoundjaïa (upper Cenomanian-lower Turonian). The western part of the Ksour Mountains, which is less documented and poorly known, is here the subject of a detailed sedimentological and palaeontological study. Near Hassi Djeifa locality (Forthassa) the upper Cretaceous is represented by the upper part of Mdaouer Formation and by the lowermost part of Rhoundjaïa Formation. The deposits attributed to the Mdaouer Formation are composed of reddish or green marlstone intercalated by biolaminated limestone, bioclastic limestone with gastropods and bivalves, and sandstone. The selachians (Mafdetia tibniensis, Baharipristis bastetiae), pycnodontiform fishes, and ostracod fauna (Damonella spp., Ilyocypris? sp., Cypridea sp., Paracypria? sp.) coming from marly beds are studied in detail. The two selachian species (Order of Rajiformes) were so far restricted to the Early Cenomanian of Egypt. Our sedimentological and palaeontological data support a probable Early Cenomanian age of the studied deposits and indicate a coastal plain palaeoenvironment continually influenced by the action of tide.     

Tardigrade Fauna of the Region between Oka and Volga Rivers (Russia) and Patterns of their Distribution in Substrates and Habitats

The region between the Oka and Volga rivers has been largely neglected with respect to tardigrade biodiversity. In the present study a total of 21 species from 7 genera, 3 families, 2 orders and only 1 class of tardigrades were present, and some of their ecological preferences were noted. The tardigrades in the studied region were mainly cosmopolitan. Eurytopic, hygrophilic and xerophilic species were common while obligate freshwater species were not found. There is a marked similarity in the tardigrade fauna within similar habitats from different locations within the region.     

Relationships between leaf thickness and vein traits of Achnatherum splendens under different soil moisture conditions in a flood plain wetland,Heihe River,China

Aims The correlations between leaf thickness and vein traits influenced the leaf hydraulic dynamic balance, and there were important meanings to reveal ecophysiological mechanisms of plant leaves water transport and growth rate. Our objective was to study the changes in the relationship between leaf thickness and vein traits (vein diameter, vein density) of Achnatherum splendenspopulations by using standardized major axis estimation (SMA) method under different soil moisture conditions located in flood plain wetland of Zhangye.Methods The study site was located at flood plains wetland of Zhangye, Gansu Province, China. Selecting a starting point along the vertical direction of the river, in turn, along the soil moisture gradient, four plots were set up at intervals of 40 m, plot I (50.07%), plot II (38.77%), plot III (31.5%) and plot IV (20.4%). From each of the four sample plots, seven samples were collected, resulting in (5 m × 5 m) a total of 28 samples. Community traits (height, density) and soil physical and chemical properties were investigated. Six individual samplings of A. splendens from each plot were used to measure the leaf thickness, vein density and vein diameter in laboratory. In addition, the photosynthetically active radiation (PAR), leaf net photosynthetic rate (P_n) and transpiration rate (T_r) of A. splendens were measured in natural environment. The 28 plots were categorized into groups I, II, III and IV, and SMA estimation method was then used to examine the allometric relationship among leaf thickness, vein density and vein diameter. Important findings With a decreased soil moisture, the plant density and height displayed a pattern of steadily declining, while the soil electrical conductivity increased, In addition, the vein density, leaf thickness, water use efficiency (WUE), PAR and twig number of A. splendens displayed a pattern of initial decrease, whereas the vein diameter and T_r increase gradually, P_n and plant high displayed changing trends of increasing-decreasing. The leaf thickness was negatively associated with the vein density, vein diameter, and the relationship varied with the soil moisture conditions (p< 0.05). There was a significant positive relationship (p < 0.05) between the leaf thickness and vein density. The SMA slope of the regression equation gradually decreased and was significantly different from 1.0 (p < 0.05) on plot I and IV. In addition, along decreased soil moisture, the standardized major axis slope of regression equation in the scaling relationships between the leaf thickness and vein diameter gradually increased and was significantly different from -1.0 (p < 0.05) on plot I and IV.     

Influence of physiographic and climatic factors on spatial patterns of acorn production in Maryland and Virginia,USA

Aim The aims of this study were to identify the effects physiographic differences have on the spatial synchrony of acorn production within red (Quercus rubra) and white (Quercus alba) oak subgenus groups, to identify climatic factors associated with acorn production patterns, and to assess if and how these relationships vary across a distinct physiographic boundary. Location Maryland and Virginia in the eastern United States. Methods Using data from 36 survey sites in Virginia (1973–2000) and Maryland (1977–2000), we described the spatial synchrony of annual acorn production based on Mantel tests and modified correlograms at three spatial scales: (1) the entire study area, (2) within two ecological regions (mountain and Piedmont), and (3) between these ecoregions. Using climate data obtained from the National Climate Data Centre, we described the relationship between climate and acorn production within each ecological region using linear regression. Results Spatial synchrony in the white oak group acorn production was strong among sites closest together, and declined with distance. The average April temperature during the year of acorn drop was positively related to acorn crop size within the mountain and Piedmont ecoregions. Spatial synchrony in the red oak group was strong among sites closest together and declined with distance in the mountain region. Synchrony was weaker in the Piedmont than in the mountain ecoregion and declined slightly with increasing distance. Between the mountain and Piedmont ecoregions, synchrony was not detected among the closest sites, but was detected with increasing strength as the distance between site pairs increased. In the Piedmont ecoregion, the number of April freeze events and total July precipitation, both 2 years prior to acorn drop, were negatively related to red oak acorn production. In the mountains, average July temperature 2 years prior to acorn drop was positively related to acorn production. Main conclusions Physiographic differences affected the spatial acorn production synchrony in the red oak but not in the white oak subgenus group. Climatic factors related to annual acorn production variability differed between subgenus groups and physiographic regions. The physiographic differences between the mountain and Piedmont ecoregions may define spatial patterns of acorn production synchrony in some oak species and mediate climatic influences on acorn production.     

Dinosaur tracks in Lower Jurassic coastal plain sediments (Sose Bugt Member,Rønne Formation) on Bornholm,Denmark

Fluvial palaeochannels of coastal plain sediments of the Lower Jurassic Sose Bugt Member of the Rønne Formation exposed in the coastal cliffs at Sose Bugt, Bornholm, contain abundant dinosaur or other large vertebrate tracks in the form of deformation structures exposed in vertical section. The tracks are represented by steep‐walled, flat‐to‐concave‐bottomed depressions, with a raised ridge at each side. The tracks are filled with laminated sediments, draping the contours of the bottom of the depression. Underprints, stacked concave deformations beneath the prints, are present beneath each track. Contemporary Upper Triassic – Lower Jurassic strata from southern Sweden and Poland contain a diverse track fauna, supporting our interpretation. This is the earliest evidence of dinosaur activity in Denmark.     

黄淮海平原典型站点冬小麦生育阶段的干旱特征及气候趋势的影响

以黄淮海平原为研究区域,选择了区域内具有代表性的5个站点,使用相对湿润度指数,从气象干旱的角度分析了近30年冬小麦各主要生育阶段干旱的时空变化特征,以及干旱特征的气候趋势影响,结果表明:(1)黄淮海平原冬小麦除苗期外其他生育阶段干旱由北向南逐渐减轻,在冬小麦播种—出苗期南部有干旱化的趋势,而北部有干旱减弱的趋势,全生育期也有相同的微弱趋势;在出苗—拔节期干旱最为严重,呈现北部微弱干旱化而南部湿润化的趋势,抽穗—成熟期呈干旱化的趋势,且从北向南干旱变化幅度递增。(2)在冬小麦全生育期,天津与石家庄主要以中旱和重旱为主,而莘县轻旱、中旱和重旱的频率相当,徐州与驻马店则以轻旱为主。天津、石家庄的干旱持续较为严重,而驻马店近30年无干旱的持续。(3)在拔节—抽穗期和抽穗—成熟期,徐州、驻马店的干旱程度随着温度的降低有减弱趋势。播种—出苗期,天津与徐州随着太阳辐射量的增加将呈干旱化的趋势;另外,石家庄与驻马店在冬小麦各生育阶段将会随着相对湿度的减小而有干旱化的趋势;黄淮海南部地区在冬小麦全生育期和抽穗—成熟期将会随着风速的减小而呈湿润化的趋势。研究结果可从关键生育期的角度为黄淮海平原干旱对冬小麦产量影响的模拟研究以及小麦生产的抗旱对策提供理论依据。