含刚性沉水植物明渠水流结构的试验研究     

王子建  丁雪  吉庆丰 《灌溉排水学报》2020,(2):78-83

【目的】得到含刚性沉水植物明渠的水流结构。【方法】采用粒子图像测速仪(PIV),用有机玻璃棒模拟刚性植物,在不同来水流量、植物密度条件下对明渠水流结构进行了试验研究。【结果】无植物时平均流速沿垂向呈对数分布规律,有植物时则呈现明显的分区分布特性。无植物时紊动强度值沿垂向变化不大,有植物时在植物顶端位置处紊动最剧烈。流量或植物密度越大,植物顶端位置的流速梯度就越大,植物层上方的流速最大值也越大。植物密度越大,植物顶端位置的紊动强度越大,植物密度对水流紊动强度由最大值减小到最小值的区域影响很大。【结论】刚性沉水植物的存在会改变水流结构,增强紊动掺混,增强流体质点交换和能量传递,且上述影响会随着流量或植物密度的增大而增强。  相似文献   

Impact of weather variables and season on sporulation of Phytophthora pluvialis and Phytophthora kernoviae     

Stuart Fraser  Mireia Gomez‐Gallego  Judy Gardner  Lindsay S. Bulman  Sandra Denman  Nari M. Williams 《Forest Pathology》2020,50(2)

Phytophthora pluvialis and Phytophthora kernoviae are the causal agents of important needle diseases on Pinus radiata in New Zealand. Little is known about the epidemiology of the diseases, making the development of control strategies challenging. To investigate the seasonality and climatic drivers of sporulation, inoculum traps, consisting of pine fascicles floating on water in plastic containers, were exchanged fortnightly at five sites in P. radiata plantations between February 2012 and December 2014. Sections of needle baits were plated onto selective media and growth of Phytophthora pluvialis and P. kernoviae recorded. To explore the generalizability of these data, they were compared to detection data for both pathogens from the New Zealand Forest Health Database (NZFHDB). Further, equivalent analyses on infection of Rhododendron ponticum by P. kernoviae in Cornwall, UK allowed the comparison of the epidemiology of P. kernoviae across different host systems and environments. In New Zealand, inoculum of P. pluvialis and P. kernoviae was detected between January–December and March–November, respectively. Inoculum of both species peaked in abundance in late winter. The probability of detecting P. pluvialis and P. kernoviae was greater at lower temperatures, while the probability of detecting P. pluvialis also increased during periods of wet weather. Similar patterns were observed in NZFHDB data. However, the seasonal pattern of infection by P. kernoviae in the UK was the opposite of that seen for sporulation in New Zealand. Phytophthora kernoviae was likely limited by warmer and drier summers in New Zealand, but by colder winter weather in the UK. These results emphasize the importance of considering both environmental drivers and thresholds in improving our understanding of pathogen epidemiology.  相似文献   

Innovating in less developed regions: What drives patenting in the lagging regions of Europe and North America     

Andrs Rodríguez‐Pose  Callum Wilkie 《Growth and change》2019,50(1):4-37

Not all economically disadvantaged—“less developed” or “lagging”—regions are the same. They are, however, often bundled together for the purposes of innovation policy design and implementation. This paper attempts to determine whether such bundling is warranted by conducting a regional level investigation for Canada, the United States, on the one hand, and Europe, on the other, to (a) identify the structural and socioeconomic factors that drive patenting in the less developed regions of North America and Europe, respectively; and (b) explore how these factors differ between the two contexts. The empirical analysis, estimated using a mixed‐model approach, reveals that, while there are similarities between the drivers of innovation in North America's and Europe's lagging regions, a number of important differences between the two continents prevail. The analysis also indicates that the territorial processes of innovation in North America's and Europe's less developed regions are more similar to those of their more developed counterparts than to one another.  相似文献   

Backshoring and nearshoring: An overview     

Benedetta Piatanesi  Josep‐Maria Arauzo‐Carod 《Growth and change》2019,50(3):806-823

Increasingly, economies that have traditionally benefited from offshoring are losing some of their strategical advantages, with a consequent increase in backshoring by developed economies. This paper describes the phenomenon and tries to shed light on the current challenges, trends, and debates in the area, and on the main determinants of backshoring. A new phenomenon known as nearshoring is also analysed—this consists of relocating some previously offshored manufacturing activities so that they are now close to previous core locations, but not so close as to suffer from disagglomeration effects. This combines the advantages of offshoring and backshoring.  相似文献   

Spatial–temporal evolution of the port–hinterland relationship: A case study of the Midstream Yangtze River,China     

Dan He  Zhijing Sun  Peng Gao  Yui‐yip Lau 《Growth and change》2019,50(3):1043-1061

Most scientific attention on port studies centers on deep sea ports, especially container ports. In this paper, in contrast, attention is focused on the spatial–temporal development of inland waterway ports on the Midstream Yangtze River from 2001 to 2013. The aim of this study is to assess two relevant and complementary questions of the hinterland evolution: its geographical extent and the coordination relationship with the inland port. To conduct the study, it was necessary to first identify the boundaries of the ports' hinterlands within the given timeframe. Then, the coupling coordination degree model was introduced to explore the underlying relationship between the port service and hinterland economy. Furthermore, to better depict the intricate economic characteristics of the hinterland, the development stage theory was applied in the models. The results highlight the emergence of a discontinuous hinterland at Wuhan Port and its reinforcement of primacy with respect to fierce hinterland rivalry. It also demonstrates that an interplay between major ports and their corresponding hinterlands evolves from the transitional stage, characterized by lagging port service, to the multi‐stage, wherein the supply of ports partly outstrips hinterland demand.  相似文献   

The role of ear environment in postharvest susceptibility of maize to toxigenic Aspergillus flavus     

Samuel K. Mutiga  Nelson Chepkwony  Owens A. Hoekenga  Sherry A. Flint‐Garcia  Rebecca J. Nelson 《Plant Breeding》2019,138(1):38-50

A kernel screening assay (KSA) was used to assess the genetic and environmental effects on the vulnerability of maize to aflatoxin accumulation. Kernels of 26 inbred lines that had been grown in seven environments, and 190 lines of the Intermated B73xMo17 (IBM) population grown in one location in the United States, were inoculated with a toxigenic strain of A. flavus and incubated in the dark at 30°C for 6 days. Percent kernel colonization (PKC), sporulation and aflatoxin were influenced by the maize genotypes (G), the location (“ear environment” or E) and the GxE interactions. Overall, low broad‐sense heritabilities were observed for PKC, sporulation and aflatoxin. PKC was significantly correlated with sporulation in all environments. Aflatoxin was positively correlated with colonization for two and with sporulation for all ear environments. Higher grain sulphur or magnesium in IBM was associated with less colonization or aflatoxin. Postharvest susceptibility of maize to aflatoxin is thus influenced by factors that are modulated by the ear environment. In a KSA, sporulation could be a proxy test for aflatoxin accumulation.  相似文献   

Development of colchicine‐induced tetraploid St. Augustinegrass (Stenotaphrum secundatum) lines     

Esdras M. Carbajal  M. Carolina Zuleta  Luellen Swayzer  Brian M. Schwartz  Maria Carolina Chavarro  A. Carolina Ballen‐Taborda  Susana R. Milla‐Lewis 《Plant Breeding》2019,138(6):958-966

St. Augustinegrass is well suited for lawns and commercial landscapes. While many genotypes are cross‐fertile, all cultivars are propagated vegetatively in sod production. To ensure varietal purity, development of sterile triploid hybrids by crossing tetraploid and diploid genotypes has been successfully used in other warm‐season turfgrasses. Applying this model in St. Augustinegrass would be beneficial to sod producers and turf managers who require purity for certification and uniformity for performance, respectively. This study was conducted to develop colchicine‐induced tetraploid lines of St. Augustinegrass. Seeds of cultivar ‘Raleigh’ were treated with four colchicine concentrations at four exposure times. A non‐treated control was included among the treatments. Seedlings that germinated were screened for genome size changes using flow cytometry. Line DSA 13005 and two progeny lines derived through selfing, DSA 16001 and DSA 16016, were corroborated as tetraploids (2n = 4x = 36) through chromosome counts. These lines will be used in future breeding efforts to attempt development of sterile triploid cultivars of St. Augustinegrass.  相似文献   

小黑麦不同品种劣变种子的胚培养效果研究     

李雪  田新会  杜文华 《草原与草坪》2018,(1):76-82

试验选用从澳大利亚引进的10个小黑麦品种的劣变种子的胚在1/2MS+2%蔗糖+0.1%麦芽糖+0.5%琼脂、pH 5.8的培养基中进行培养。结果表明:劣变小黑麦品种种子胚的发育率和成苗率由高到低分别为:DH265Cherokee2090WhiteAT528WhileM96-3182-1AT754AT315和CherokeeDH2652090WhiteAT528WhileM 96-3182-1AT754AT315,试验材料的胚发育率和成苗率均显著低于正常小黑麦材料(CK1,CK2);小黑麦品种33rd ITSN,32rd ITSN和Rhino的胚发育率和成苗率均为0;劣变小黑麦种子进行胚培养时,诱导培养的适宜时间为27d。  相似文献   

干旱胁迫下不同品种杨树矿质离子含量变化     

朱桐  金华  邹吉祥  李新林  金纯伊  程文琼  刘思佳 《中南林业科技大学学报(自然科学版)》2020,(2):102-107

【目的】了解杨树在干旱胁迫下矿质离子分布及其动态变化。【方法】以吴屯杨、新疆杨和荷兰杨为实验材料,在中度和重度干旱条件下测定了根、茎、叶和质外体的K^+、Ca^2+、Na^+和Mg^2+等4种离子含量的变化。【结果】干旱胁迫使K^+、Ca^2+和Na^+离子含量上升,Mg^2+含量下降,其中K^+和Ca^2+含量自胁迫开始明显升高,Na^+含量则在中度胁迫之后明显增加。离子在各器官分布情况为:K^+主要分布于杨树的叶片,Ca^2+、Na^+和Mg^2+主要分布于杨树根部,且离子分布存在品种间差异,荷兰杨和新疆杨中K^+分布为:叶>根>茎,而吴屯杨体内K^+分布则为:叶>茎>根;3种杨树中Ca^2+分布均为:根>叶>茎;吴屯杨和荷兰杨中Na^+分布为:根>茎>叶,新疆杨则为:根>叶>茎;在Mg^2+的分布上吴屯杨和新疆杨较为类似即:根>叶>茎,而荷兰杨为叶>根>茎。【结论】干旱胁迫下杨树首选吸收的离子是K^+和Ca^2+,K^+主要分布在杨树的叶片中,其次是根部,Ca^2+主要分布在杨树的根部。重度干旱胁迫下,杨树开始吸收Na^+,储存在杨树的根部。不同品种杨树之间离子的分布和吸收都存在品种差异。质外体作为离子的运输通道,在各干旱条件下运输4种矿质离子至杨树的其他部位,Mg^2+存在滞留在质外体中的情况。本研究可为植物在干旱胁迫下矿质离子吸收和分布的研究提供理论依据。  相似文献   

Development of a core set of KASP markers for assaying genetic diversity in Brassica rapa subsp. chinensis Makino     

Peirong Li  Tongbing Su  Huiping Wang  Xiuyun Zhao  Weihong Wang  Yangjun Yu  Deshuang Zhang  Changlong Wen  Shuancang Yu  Fenglan Zhang 《Plant Breeding》2019,138(3):309-324

Single‐nucleotide polymorphisms (SNPs) are rapid, economical and reliable genotyping tools. Non‐heading Chinese cabbage (Brassica rapa L. subsp. chinensis Makino) is now an economically important vegetable crop worldwide. In this study, 1,167 SNPs were evaluated for 7polymorphism among 70 representative non‐heading Chinese cabbage inbred lines using a Kompetitive Allele Specific PCR (KASP) genotyping assay. On the basis of identified polymorphisms and the results of a principal component analysis, we selected 50 core SNPs that were balanced sufficiently to provide adequate information for genetic identification. The core SNPs were used for construction of a neighbour‐joining dendrogram that separated the 70 inbred lines into four main groups and several subgroups corresponding to Caixin, Heiyebaicai, Huangxinwu, Naibaicai, Taitsai, Pak‐choi, and Wutatsai. This categorization was superior to that achieved using a dataset of 479 polymorphic SNPs. To confirm the utility of the core SNP markers in genetic identification, we tested their stability and resolution using 162 commercial hybrid cultivars. The SNPs, which represent a cost‐effective, accurate marker set for germplasm analysis and cultivar identification, are suitable for molecular marker‐assisted breeding in non‐heading Chinese cabbage.  相似文献