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21.
为进一步了解木本植物不定根发生、发育的机理,对苹果砧木M26试管苗不定根的发生、发育过程进行解剖观察,利用十二烷基磺酸钠聚丙烯酰胺凝胶电泳(SDS-PAGE)对M26试管苗在接入生根培养基前后,不同时期表达的蛋白进行了研究。结果发现:在不定根原基形成和发育的阶段性过程中,茎基部蛋白质的种类和数量出现明显差异。生根培养后,在继代苗茎基部表达的5条蛋白条带减弱或消失,其分子量分别为26.8 kDa、37kDa、40.3 kDa、43 kDa和66 kDa;明显表达了4条新的蛋白条带,其分子量分别为26 kDa、27.7 kDa、32.5 kDa、和45 kDa,同时有4条蛋白条带(38.5 kDa、42 kDa、53.2 kDa和55.5 kDa)其表达丰度提高。多种蛋白条带的消失和出现,可作为M26试管苗不定根产生的生化标志。在不定根原基逐步形成发育的同时,有3条蛋白条带的表达丰度也逐步提高,可作为不定根形成过程表达的特异标记蛋白带。 相似文献
22.
Peach tree replant disease, though reported on in the literature for more than two centuries, has yet to have its causes clearly defined. Decline in peach productivity has been attributed to toxic agents, insects, nutritional disturbances, spray residues, fungi and nematodes. Bacteria has also been indicated as a contributing factor.Peach replant disease was reproduced by using two successive cultures on the same soil. Bacterial communities were isolated and characterized from healthy and diseased peach trees. The potential role of cyanide production by rhizobacteria in the replant problem of peaches was studied. Culture-dependent (evaluation of the number of culturable bacteria, metabolic activities, Biolog® GN2) and independent (ribosomal intergenic spacer analysis, RISA) methods were used, in order to compare bacterial community structure and diversity in healthy and sick soils and to evaluate the possible role of cyanide.Bacterial densities were significantly increased in sick soils. Metabolic activities (Biolog® GN2) and genetic structure, observed through RISA, were also significantly modified in sick soils. Changes in the composition of individual microbial groups in the rhizosphere of peach trees excavated from healthy or sick soil indicated the involvement of rhizobacteria in the etiology of the replant sickness of peach soil. More than 60% of the strains isolated from healthy soils corresponded to Pseudomonas sp. and 58% of the isolates from sick soils were Bacillus sp. This study determined that Bacillus were able to produce in vitro HCN. It also appeared that in sick soil, there was a shift in the structure of bacterial communities with an increase noted in phytotoxic microorganisms capable of producing HCN compounds. 相似文献
23.
为探讨近三十年来我国皱纹盘鲍养殖模式对群体遗传结构产生的影响,利用线粒体细胞色素C氧化酶亚基 (
24.
Naugle David E. Higgins Kenneth F. Nusser Sarah M. Johnson W. Carter 《Landscape Ecology》1999,14(3):267-276
We evaluated the influence of scale on habitat use for three wetland-obligate bird species with divergent life history characteristics and possible scale-dependent criteria for nesting and foraging in South Dakota, USA. A stratified, two-stage cluster sample was used to randomly select survey wetlands within strata defined by region, wetland density, and wetland surface area. We used 18-m (0.1 ha) fixed radius circular-plots to survey birds in 412 semipermanent wetlands during the summers of 1995 and 1996. Variation in habitat use by pied-billed grebes (Podilymbus podiceps) and yellow-headed blackbirds (Xanthocephalus xanthocephalus), two sedentary species that rarely exploit resources outside the vicinity of nest wetlands, was explained solely by within-patch variation. Yellow-headed blackbirds were a cosmopolitan species that commonly nested in small wetlands, whereas pied-billed grebes were an area-sensitive species that used larger wetlands regardless of landscape pattern. Area requirements for black terns (Chlidonias niger), a vagile species that typically forages up to 4 km away from the nest wetland, fluctuated in response to landscape structure. Black tern area requirements were small (6.5 ha) in heterogeneous landscapes compared to those in homogeneous landscapes (15.4–32.6 ha). Low wetland density landscapes composed of small wetlands, where few nesting wetlands occurred and potential food sources were spread over large distances, were not widely used by black terns. Landscape-level measurements related to black tern occurrence extended past relationships between wetlands into the surrounding matrix. Black terns were more likely to occur in landscapes where grasslands had not been tilled for agricultural production. Our findings represent empirical evidence that characteristics of entire landscapes, rather than individual patches, must be quantified to assess habitat suitability for wide-ranging species that use resources over large areas. 相似文献
25.
对石河子市土地利用结构进行了评价。结果表明,石河子市正处于经济发展的加速阶段,城市化进程还在加快,土地利用结构也处于不断变化之中。同时分析了石河子市土地利用结构存在的问题。 相似文献
26.
27.
In Central Europe, various plant species including large-grain legumes and their mixtures are grown as catch crops, particularly between grains harvested early and subsequent summer crops. This article investigates the question of how soil structure in the topsoil is influenced when catch cropping with large-grain legumes (experimental factor A: without catch crop, with catch crop) under different ploughless tillage conditions during catch crop seeding (experimental factor B: deep tillage/25–30 cm, shallow tillage/8–10 cm). Five one-year trials were performed using standard machinery at various sites in Germany. Soil core samples extracted from the topsoil in the spring after catch crop cultivation served to identify air capacity, saturated hydraulic conductivity and precompression stress. The above-ground and below-ground biomass yields of the catch crops were also determined at most of the sites. In addition, the soil compaction risk for the working steps in the experiments was calculated using the REPRO model.The dry matter yield of the catch crops varied considerably between the individual trial sites and years. In particular, high levels of dry matter were able to form in the case of early seeding and a sufficient supply of precipitation. The soil structure was only rarely affected positively by catch crop cultivation, and catch crops did not contribute in the short term to loosening already compacted topsoils. In contrast, mechanical soil stresses caused by driving over the ground and additional working steps used in cultivating catch crops often led to lower air capacity in these treatments. This is consistent with the soil compaction risks calculated using the REPRO model, which were higher in the treatments with catch cropping. Catch crop cultivation also only resulted in improved mechanical stability at one location. The positive effect of deep ploughless tillage on air capacity and saturated hydraulic conductivity, however, became more clearly evident regardless of catch crop cultivation. In order for catch crop cultivation with large-grain legumes to be able to have a favourable impact on soil structure, it is therefore important that cultivating them does not result in any new soil compaction. In the conditions evaluated, deep tillage was more effective at loosening compacted topsoil than growing catch crops. 相似文献
28.
在对比分析国内外报废汽车回收利用的基础上,指出当前我国报废汽车回收中存在的不足;阐述了绿色回收的定义,进一步分析汽车的生命周期及其各阶段产生的回收源和流向,并构建了汽车全生命周期绿色回收体系结构模型;最后,提出我国今后促进报废汽车绿色回收发展应采取的策略. 相似文献
29.
消费结构不仅是消费领域的重要问题,而且也关系到整个社会经济的发展。正确认识居民消费结构现状,有利于产业结构和产品结构的调整,有利于调节供求矛盾,而且对于正确引导居民消费、实现消费结构的合理化有重要的现实意义。根据2005—2009年聊城市城乡居民消费结构数据,分析发生的变化,进而分析其产生差异的原因,为促进经济增长,改善人民生活提供可行性的建议。 相似文献
30.
Craig G. Lorimer Daniel J. Porter Mary Ann Madej John D. Stuart Stephen D. Veirs Jr. Steven P. Norman Kevin L. OHara William J. Libby 《Forest Ecology and Management》2009,258(7):1038-1054
Coast redwood (Sequoia sempervirens), a western North American conifer of ancient lineage, has a paradoxical combination of late-successional characteristics and strong adaptations to disturbance. Despite its shade tolerance and heavy dominance of the canopy on many sites, redwood saplings are uncommon in upland old-growth stands. Information needed to ensure the conservation of old-growth redwood forests has been limited. In this review paper, we integrate evidence on redwood biology with data on the historic and modern disturbance regimes to help clarify the degree to which key attributes of redwood forests may have been dependent upon periodic disturbance. Available evidence suggests that episodes of fire, flooding, and slope failure prior to European settlement were frequent but predominantly of low to moderate severity and extent, resulting in broadly uneven-aged forests. The majority of fires prior to European settlement were apparently of human origin. Frequency and severity of the major disturbance agents have been radically changed in modern times. Fires have been largely excluded, and flooding has been altered in ways that have often been detrimental to old-growth redwoods on alluvial terraces. However, because of the apparent anthropogenic origin of most presettlement fires, the long-term evolutionary role of fire for coast redwood is ecologically ambiguous. With fire exclusion, redwood possibly could be displaced to some extent on upland sites by increasing abundance of fire-sensitive competitors. Alternatively, redwood may be able to maintain dominance by vegetative sprouting and new seedling establishment on root-wad mounds, fallen logs, and on soil exposed by slope failure. Future research priorities are suggested that will help resolve some of the current ambiguities. 相似文献