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81.
信息经济学与图书馆学的相互契合渗透和影响,促进了图书馆学的发展,扩大了其研究对象,深化了图书馆学的发展,这对于认识图书馆学“名”和“实”的歧见是有启示的。 相似文献
82.
Breeding against mycorrhizal symbiosis: Modern cotton (Gossypium hirsutum L.) varieties perform more poorly than older varieties except at very high phosphorus supply levels 下载免费PDF全文
Cotton (Gossypium hirsutum L.) is an important fiber cash crop, but its root traits related to phosphorus (P) acquisition, including mycorrhizal root traits, are poorly understood. Eight cotton varieties bred in northwestern China that were released between 1950 and 2013 were grown in pots with or without one arbuscular mycorrhizal fungal (AMF) species (Funneliformis mosseae) at three P supply levels (0, 50 and 300 mg P as KH2PO4 kg–1). Eleven root traits were measured and calculated after 7 wk of growth. The more recent accessions had smaller root diameters, acquired less P and produced less biomass, indicating an (inadvertent) varietal selection for thinner roots that provided less cortical space for AMF, which then increased the need for a high P fertilizer level. At the two lower P levels, the mycorrhizal plants acquired more P and produced more biomass than non-mycorrhizal plants (3.2 vs. 0.9 mg P per plant; 1.8 vs. 0.9 g biomass per plant at P0; 14.5 vs. 1.7 mg P per plant; and 4.7 vs. 1.6 g biomass per plant at P50). At the highest P level, the mycorrhizal plants acquired more P than non-mycorrhizal plants (18.8 vs. 13.4 mg per P plant), but there was no difference in biomass (6.2 vs. 6.3 g per plant). At the intermediate P level, root diameter was significantly positively correlated with shoot biomass, P concentration and the P content of mycorrhizal plants. The results of our study support the importance of the outsourcing model of P acquisition in the root economics space framework. Inadvertent varietal selection in the last decades, resulting in thinner roots and a lower benefit from AMF, has led to a lower productivity of cotton varieties at moderate P supply (i.e., when mycorrhizal, the average biomass of older varieties 5.0 g per plant vs. biomass of newer varieties 4.4 g per plant), indicating the need to rethink cotton breeding efforts in order to achieve high yields without very high P input. One feasible way to solve the problem of inadvertent varietal selection for cotton is to be aware of the trade-offs between the root do-it-yourself strategy and the outsourcing towards AMF strategy, and to consider both morphological and mycorrhizal root traits when breeding cotton varieties. 相似文献
83.
通过对辽宁东部山区的自然资源和生态经济发展状况的分析,指出目前东部山区生态经济发展中存在的一些问题及必须走生态经济持续发展之路。同时提出了生态经济持续发展的指导思想和原则,为今后制定东部山区生态经济持续发展提供依据。 相似文献
84.
Economics of Sustainable Intensification of Aquaculture: Evidence from Shrimp Farms in Vietnam and Thailand 下载免费PDF全文
Carole R. Engle Aaron McNevin Phoebe Racine Claude E. Boyd Duangchai Paungkaew Rawee Viriyatum Huynh Quoc Tinh Hang Ngo Minh 《Journal of the World Aquaculture Society》2017,48(2):227-239
There is growing interest in sustainable intensification of aquaculture production. Yet little economic analysis has been done on farm‐level effects of the economic sustainability of production intensification. Data from 83 shrimp farms (43 in Vietnam and 40 in Thailand) were used to identify (through principal component and cluster analyses) 13 clusters of management practices that reflected various scales of production intensity that ranged from 0–1999 kg/ha/crop to 10,000 kg/ha/crop and above, for both Penaeus monodon and Litopenaeus vannamei in Vietnam and Thailand. The clusters identified reflected sets of management practices that resulted in differing yields despite similarities in stocking densities among some clusters. The enterprise budget analysis developed showed that the more intensively managed clusters outperformed the less intensively managed clusters in economic terms. More intensively managed farm clusters had lower costs per metric ton of shrimp produced and were more profitable. The greater yields of shrimp produced per hectare of land and water resources in more intensively managed shrimp farms spread annual fixed costs across a greater volume of shrimp produced and reduced the cost per metric ton of shrimp. Costs per metric ton of shrimp produced decreased from the lowest to the highest intensity level (from US$10,245 at lowest intensity to US$3484 at highest for P. monodon and from US$24,301 to US$5387 for L. vannamei in Vietnam and from US$8184 at the lowest intensity level to US$3817 at the highest intensity level per metric ton for L. vannamei in Thailand). Costs of pond amendments used in shrimp production were particularly high in Vietnam and largely unwarranted, whereas fixed costs associated with the value of land, production facilities, equipment, and labor were sufficiently high in Thailand so that net returns were negative in the long run. Nevertheless, economic losses in Thailand were less at greater levels of intensification. The study demonstrated a clear value proposition for shrimp farmers to use natural resources (such as land) and other inputs in an efficient manner and supports findings from corresponding research on farm‐level natural resource use efficiency. Additional research that incorporates economic analysis into on‐farm studies of sustainable intensification of aquaculture is needed to provide ongoing guidance related to sustainable management practices for aquaculture. 相似文献
85.
Luc Doyen Christophe Béné Michel Bertignac Fabian Blanchard Abdoul Ahad Cissé Catherine Dichmont Sophie Gourguet Olivier Guyader Pierre‐Yves Hardy Sarah Jennings Lorne Richard Little Claire Macher David Jonathan Mills Ahmed Noussair Sean Pascoe Jean‐Christophe Pereau Nicolas Sanz Anne‐Maree Schwarz Tony Smith Olivier Thébaud 《Fish and Fisheries》2017,18(6):1056-1072
Reconciling food security, economic development and biodiversity conservation is a key challenge, especially in the face of the demographic transition characterizing many countries in the world. Fisheries and marine ecosystems constitute a difficult application of this bio‐economic challenge. Many experts and scientists advocate an ecosystem approach to manage marine socio‐ecosystems for their sustainability and resilience. However, the ways by which to operationalize ecosystem‐based fisheries management (EBFM) remain poorly specified. We propose a specific methodological framework—viability modelling—to do so. We show how viability modelling can be applied using four contrasted case‐studies: two small‐scale fisheries in South America and Pacific and two larger‐scale fisheries in Europe and Australia. The four fisheries are analysed using the same modelling framework, structured around a set of common methods, indicators and scenarios. The calibrated models are dynamic, multispecies and multifleet and account for various sources of uncertainty. A multicriteria evaluation is used to assess the scenarios’ outcomes over a long time horizon with different constraints based on ecological, social and economic reference points. Results show to what extent the bio‐economic and ecosystem risks associated with the adoption of status quo strategies are relatively high and challenge the implementation of EBFM. In contrast, strategies called ecoviability or co‐viability strategies, that aim at satisfying the viability constraints, reduce significantly these ecological and economic risks and promote EBFM. The gains associated with those ecoviability strategies, however, decrease with the intensity of regulations imposed on these fisheries. 相似文献
86.
87.
通过实际测算的各种数据,对利用电机抽水进行农田灌溉的直接费用与柴油机抽水的费用进行对比。对比结果充分说明了利用电力灌溉是很有推广价值的,节约了灌溉的投入资金,其效益十分可观;同时对投资的方法进行了探讨 相似文献
88.
89.
以江苏为例,阐述了城乡统筹发展是在加快城市化发展的基础上,强化城市主体辐射带动作用,促进城乡各种要素双向流动、优势互补,实现资源共享和合理配置,缩小城乡差别,实现城乡经济社会的和谐发展,使城乡共享现代文明的一种社会系统建设。城乡统筹发展不仅强调城乡经济一体化,同时要求城乡社会各项事业一体化,包括经济布局、科教文卫事业、户籍管理、劳动就业、社会保障、基础设施和生态环境建设一体化。为此,要用科学发展观统筹城乡发展,解决新时期农业、农村和农民问题,最终打破中国社会城乡分割的二元经济结构,进而实现全面小康的目标。 相似文献
90.
Nicholas Andrew Robinson Glenn Schipp Jérôme Bosmans Dean Robert Jerry 《Aquaculture Research》2010,41(10):e643-e655
A bioeconomic simulation model for Lates calcarifer predicted that a strategy involving crossing current generation males with previous generation females would be a practical, effective and profitable way of dealing with protandry when batch rearing for selective breeding to improve the growth rate. The strategy allowed earlier initialization and more frequent ongoing rounds of selection, and resulted in a 16–19% higher overall response, than an alternative where each generation's males were crossed with the same generation's females. The strategy also yielded the highest short‐term benefit–cost ratio (13:1 versus 7:1 after 8 years of selective breeding) and the highest short‐ and long‐term value for participants in a breeding cooperative (a net present value of AU$28 million and an internal rate of return of 144% over 10 years), due to higher yields per fixed costs of production per unit area and due to savings in feed costs per kilogram of production. Breeding facilities of scale producing 50 full‐sibling families per generation were found to be more profitable than those producing 100 families. 相似文献