中国的经济环境政策及退耕还林还草政策取向

在对中国环境经济政策内涵及作用分析的基础上,针对西欧环境经济政策成功的经验及对中国的启示：政府与农户签订长期合同、发放补助金和实施减免税政策等。并结合中国西部地区退耕还林的调研结果述评,提出了中国退耕还林政策的取向：实行长期的补贴政策、尊重农户意愿、改善林业投资环境、对退耕还林成果实行产业化经营运作等。     

Stage Sensitivity of Mungbean (Vigna radiata L. Wilczek) to an Elevated Level of Carbon Dioxide

An experiment was undertaken using open‐top chambers to study the effect of CO₂ enrichment on crop growth and to assess the variation related to the time of CO₂ exposure. In general, enriched CO₂ conditions (600 ± 50 p.p.m.) in the chamber positively affected the growth and development of mungbean (Vigna radiata), a short‐duration (60–65 days) summer pulse crop. However, there was significant variability in the effect of the crop stage/time of CO₂ exposure. It was observed that high CO₂ exposure at an early growth stage [0–20 days after germination (DAG)] had a larger effect than that at a later growth stage (21–40 DAG). The experiment also provided a means of assessing the short‐ and long‐term effects of elevated CO₂ on the carbon exchange rate at both stages of exposure. The study revealed that the sensitivity of plants to high CO₂ was more pronounced with respect to net photosynthetic rate. The overall photosynthetic activity gave greater growth and development of plants under high CO₂.     

Comparison of two fertility restoration systems against photoperiod-sensitive cytoplasmic male sterility in wheat

A ‘two‐line system’ using photoperiod‐sensitive cytoplasmic male sterility (PCMS) caused by Aegilops crassa cytoplasm under a long‐day photoperiod ( 15 h) has been proposed as a new means of producing hybrid varieties in common wheat. The PCMS line is maintained by self‐pollination under short‐day conditions, and hybrid seeds can be produced through outcrossing of the PCMS line with a pollinator under long‐day conditions. Two kinds of fertility restoration systems against the PCMS are known. One is involved with a set of multiple fertility‐restoring (Rf) genes in the wheat cultivar ‘Norin 61’ located on (at least) chromosomes 4A, 1D, 3D and 5D. The other is controlled by a single dominant major Rf gene, Rfd1, located on the long arm of chromosome 7B in the wheat cultivar ‘Chinese Spring’. To examine the degree of fertility restoration by these two systems, nine PCMS lines were crossed with ‘Norin 61’ and ‘Chinese Spring’ as the restorer lines, and the F₁ hybrids were investigated. The degree of fertility restoration was estimated by comparing the seed set rates in the F₁ hybrids having the Ae. crassa cytoplasm and those with normal cytoplasm. The results revealed that the fertility restoration ability of a set of multiple Rf genes in ‘Norin 61’ was higher than that of the Rfd1 gene in ‘Chinese Spring’.     

Deregulation in the Electric Utility Industry: Excess Capacity and the Transition to a Long‐Run Competitive Market

ABSTRACT Existing analyses of electricity deregulation have focused on situations where horizontal market power is present. This paper instead evaluates a market where a competitive outcome is more likely. Competitive market supply and demand curves for electricity have been simulated for a twenty‐state region. These simulated supply and demand curves are used to predict short‐run and long‐run prices for electric power. Many consumers will see a drop in the portion of their electric bills accounted for by the current economic costs of supplying them with electricity. Adjustments to consumers’ bills for stranded cost recovery will be determined by legislators and regulators on a state‐by‐state and utility‐by‐utility basis. Because of excess capacity that currently exists in the industry, the decline in prices will be greater in the short run than in the long run.     

Maize Yields as Affected by Short- and Long-Term Improved Fallows: A Comparative Analysis in the Asian Humid Tropics

Improved short‐ or long‐term fallows are considered suitable low external input technologies for maintaining productivity and sustainability of tropical smallholder upland cropping units, although comparisons on the benefits of this technology are not widely reported. A field study evaluated the impact of improved short (6 months) and long‐term fallow (18 months) using Crotalaria juncea and Tithonia diversifolia, in relation to a natural fallow of the same durations, on the productivity of maize (Zea mays), the most important upland cereal in tropical Asia, over a minor season. The use of improved fallows, especially Tithonia, increased maize yields over the Crotalaria or natural fallow. While the overall yields of maize after a long fallow were greater, the beneficial impact of the green manures was significantly higher in the short fallows. The causal factors for this trend, including biomass production of the improved fallows and possible impact on soils, along with the greater benefits of short‐term fallows for increasing maize yields in the tropics due to lower requirements of unproductive time are presented.     

The Appreciative System of Urban ICT Policies: An Analysis of Perceptions of Urban Policy Makers

ABSTRACT Information and Communication Technology (ICT) has become an important tool to promote a variety of public goals and policies. In the past years much attention has been given to the expected social benefits from deploying ICTs in different urban fields (transportation, education, public participation in planning, etc.) and to its potential to mitigate various current or emerging urban problems. The growing importance of ICTs in daily life, business activities, and governance prompts the need to consider ICTs more explicitly in urban policies. Alongside the expectation that the private sector will play a major role in the ICT field, the expected benefits from ICTs also encourage urban authorities to formulate proper public ICT policies. Against this background, various intriguing research questions arise. What are the urban policy‐makers’ expectations about ICTs? And how do they assess the future implications of ICTs for their city? A thorough analysis of these questions will provide a better understanding of the extent to which urban authorities are willing to invest in and to adopt a dedicated ICT policy. This study is focusing on the way urban decision‐makers perceive the opportunities of ICT policy. After a sketch of recent development and policy issues, a conceptual model is developed to map out the driving forces of urban ICT policies in cities in Europe. Next, by highlighting the importance of understanding the decision‐maker's “black box,” three crucial variables are identified within this box. In the remaining part of the paper these three variables will be operationalized by using a large survey comprising more than 200 European cities. By means of statistical multivariate methods (i.e., factor and cluster analysis), the decision‐makers were able to be characterized according to the way they perceive their city (the concept of “imaginable city”), their opinion about ICT, and the way they assess the relevance of ICT policies to their city. Next, a solid explanatory framework will be offered by using a log‐linear logit analysis to test the relationships between these three aspects.     

Short-and Long-Term Effects of the Construction Industry on the Economy Growth

The construction industry could be developed as a pillar industry of the national economy,since it has a strong pulling role in economic growth.However,little definite empirical evidence supports this argument.Using co-integration and Granger causality tests and error-correction model with taking Sichuan for an example,this article studies both short-term and long-term effects of the construction industry on the economy growth.Empirical tests show that in the long term the economy maintained equilibrium relations with the construction industry.A growth in the construction industry will lead to the economic growth;however the pulling role of the construction industry on the economy is limited.A growth in the construction industry will not predict economic growth in the short run.Thus,for Sichuan case the government is unable to stimulate the economy by focusing on development of the construction industry in the short run.Instead,in order to promote long-term development of the national economy it could implement stable and healthy development policies for the construction industry.     

Low‐Income Dynamics in Canadian Communities: A Place‐Based Approach

ABSTRACT Canadian poverty rates have persisted at disappointingly high levels despite almost 15 years of continuous economic growth. The problem is exacerbated by some communities and neighborhoods having exceedingly high poverty, including very high rates for vulnerable demographic groups, such as aboriginals and recent immigrants. We investigate low‐income rates (poverty rates) for 2,400 Canadian “communities” over the 1981–2001 period. By focusing on communities, we fill a void in the related Canadian literature, which tends to focus on individuals, case studies, or more aggregate measures, such as provinces. Our approach allows us to assess the role of place‐based policies. Particular attention is given to communities with differing shares of aboriginal Canadians and recent immigrants. One novel feature is our analysis of both “short‐term” and “long‐term” causes of differential community poverty rates. The results suggest that community low‐income rates are more affected by initial economic conditions in the short term, with certain demographic factors becoming relatively more important in the long run.     

The Dynamic Effects of Entrepreneurship on Regional Economic Growth: Evidence from Canada

Facilitating entrepreneurship to address regional income disparity continues to be a major concern of policy makers across the globe. This study explores the temporal pattern of income disparity for Canadian provinces in two estimation steps. First, an econometric growth regression model is applied to identify the impact of entrepreneurship on regional economic growth. The estimation results suggest that entrepreneurship, measured in terms of the self‐employment rate, plays a pivotal role in determining regional development in Canada. Second, a dynamic vector autoregression model is employed to simulate long‐run regional growth effects that result from policy shocks affecting entrepreneurship. Compared to other growth drivers, entrepreneurship is found to have more pronounced and long‐term stimulative effects on regional development for the period of 1987–2007.     

Validation of the two-gene epistatic model for vernalization response in a winter × spring barley cross

A two gene epistatic model in which a dominant “winter growth habit” allele at Vrn-H2 encodes a repressor with a corresponding binding site in a recessive vrn-H1 allele explains the vernalization response phenotypes in an array of barley germplasm. In order to validate the model genetically, we developed an F ₂ population (and F ₂-derived F ₃ families) from the cross of Hardy (winter) × Jubilant (spring). Using gene-specific primers, we determined the Vrn-H1 and Vrn-H2 allele architecture of each F ₂ plant and we measured the growth habit phenotype of each F ₂ plant via phenotyping of its F ₃ progeny under controlled environment conditions. We used a set of treatments involving plus/minus vernalization under long photoperiod and vernalization under short photoperiod. Alleles at the two loci showed expected patterns of segregation and independent assortment. Under long day conditions, the two Vrn genes were the primary determinants of heading date, regardless of the vernalization treatment. Under short photoperiod, the effects of these loci were not significant. There was incomplete dominance at Vrn-H1: heterozygotes were significantly later to head than Vrn-H1Vrn-H1 genotypes. Vrn-H2 genotypes were also significantly later to head, even when plants were vernalized. These results validate the two-gene epistatic model for vernalization response under long-day conditions. The results under short photoperiod, and the variance in flowering with vernalization, confirm that while the two Vrn genes are the primary determinants of vernalization response, they are part of a larger interactome that determines the timing of the vegetative to reproductive transition.     

Influence of high temperature on the performance of some Phaseolus species at different developmental stages

Summary The effect of short term high temperature exposure on the performance of five Phaseolus species and of long term (continuous) exposure on the performance of P. vulgaris was studied at three growth stages. Phaseolus species subjected to 26.7, 32.2 or 37.3°C for two days showed small differences in the number of pods produced and in visual leaf damage, but large differences in leaf heat killing time, as measured by conductivity. P. coccineus had the shortest heat killing time (20–60 minutes) and P. acutifolius and P. lunatus the longest times (180 and 153 minutes), respectively. The P. vulgaris genotypes were intermediate in killing times to P. acutifolius and P. coccineus. Species response was not consistent with temperature within developmental stage. On average, the number of pods decreased as temperature increased from 32.2 to 37.3°C. Heat killing time and leaf damage also increased with temperature. CO₂ exchange rates of plants grown at prolonged high temperatures (30–40°C/20–30°C, day/night) decreased with the age of the plant. Shoot lenght was decreased as high temperature. P. vulgaris genotypes differed on the basis of either short term exposure or of continuous exposure. These results suggest that there may be useful germplasm in Phaseolus for improving heat tolerance.Scientific Journal Series Paper Number 13,8000 of the Minnesota Agricultural Experiment Station, USA.     

Services in Regional Employment Change

This article examines the role of services in regional employment change in Illinois from 1972–87. The approach applies recent advances in time-series analysis to investigate both the long-term and short-term relationship among employment in three sectors: goods production, export-potential services, and local services. The results indicate that there is not a long-term relation among these variables, i.e., that they do not move together in the long run. In the short term, the evidence is that employment in the service sectors follows employment change in goods production, although the response persists for only six months. The results suggest that a policy of targeting export-potential services is not likely to produce sustained employment growth in the other sectors.     

Erhaltung der Ertragsfähigkeit des Bodens auf lange Sicht unter dem Einfluß von Fruchtfolgegestaltung, Düngung und Herbizideinsatz

Impact of crop rotation, fertilizer treatments, and herbicidal applications on the long term maintenance of soil fertility
VI. Examination of progressive differences regarding chemical and physical factors of the yield potential of a soil conducted over the period 1973 through to 1983
In order to investigate the influence of different crop management practices such as crop rotation, fertilizer treatments, and herbicide applications on the yield potential of a soil, the Crop Science Department of the Swiss Federal Institute of Technology (ETH Zürich) conducted a long term field experiment commencing 1973. The experimental location was at the Swiss Federal Research Station for Farm Management and Agricultural Engineering at Tänikon/TG (northeastern Switzerland).
Over ten years of research it was found that chemical and physical soil properties had, in general, been only marginally affected by the different experimental treatments. However, consistent studies have shown that certain trends regarding specific factors of greater importance have emerged, which were not observed during the first five year period. Should they persist, the yield potential of the soil could be substantially affected in the long run.
Soil reaction, organic carbon content, cation exchange capacity, and aggregate stability have proven to be relatively stable values. Changes of greater significance were evidenced regarding the character of the air-water regime, a factor of particular importance for this site. Obviously, crop rotation had a marked impact on soil compaction. Therefore under local research conditions, the yield potential of the soil will, in the short term, be most likely endangered by structural soil changes.     

1H-NMR Method Enables Early Identification of Degeneration in the Quality of Sweet Potato Tubers

In sweet potato tuber, which is a tropical plant, long‐term storage leads to loss of water and carbohydrate, thus water mobility was investigated using ¹H‐NMR spectroscopy. Electrolyte leakage indicated that tubers stored at 15 °C for 1 year were partly injured and that frozen‐thawed tissues were dead. Nuclear magnetic resonance (NMR) spin–lattice relaxation time (T₁) and spin–spin relaxation time (T₂) clearly increased with the duration of storage, whereas these values decreased in the dead tissues. Furthermore, Arrhenius plots for T₁ and T₂ were determined at temperatures ranging from 20 to 0 °C in 2.5 °C steps. In the fresh tubers, a strong converse temperature dependency was shown in the T₂ measurement. On the contrary, there was no temperature dependency in the T₂ of the dead tissues. Thus, the existence of inverse temperature dependency reflected tissue viability. Additionally, any change in the T₂ of the fresh tubers occurred at about 14 °C, which virtually coincided with the storage temperature of 15 °C. The slope change in T₂ might have responded to a physiological change as a primary event. In conclusion, monitoring water status by NMR could provide early identification of changes in the quality of post‐harvest crops; this method shows great promise for use in environmental‐stressed crop yield research.     

The Impact of Migration on Social Capital: Do Migrants Take Their Bowling Balls with Them?

Questions surrounding the impact of population migration on social capital is the focus of this study. Putnam observed that “for people as for plants, frequent repotting disrupts root systems. It takes time for a mobile individual to put down new roots.” However, because of a trending decrease in mobility over time, Putnam rules out migration as an explanation for the long‐term decline in social capital that was the subject of his widely read 1995 book Bowling Alone: America's Declining Social Capital. This study undertakes an empirical examination of the impact of migration on county‐level social capital, which in tribute to Putnam one might view as an attempt to answer the question—do migrants take their bowling balls with them when they move? The potential for county‐level migration of population to impact social capital levels at particular locations in space arises from the conventional argument that social capital promotes trust and cooperation among agents. This trust increases socially efficient collective action but requires investment in relationships and commitment of scarce resources to build social capital. It seems plausible that migration of population might have a negative impact on the stock of social capital by interfering with trust and cooperation among agents. However, it is also possible that migrants may take their social capital with them to new places of residence. In other words, the propensity to join social and civic organizations might reflect inherent traits of individuals who are willing to make commitments of their resources to building social capital in any community where they reside.     

Identification of qRL7, a major quantitative trait locus associated with rice root length in hydroponic conditions

Root system development is an important target for improving yield in rice. Active roots that can take up nutrients more efficiently are essential for improving grain yield. In this study, we performed quantitative trait locus (QTL) analyses using 215 recombinant inbred lines derived from a cross between Xieqingzao B (XB), a maintainer line with short roots and R9308, a restorer line with long roots. Only a QTLs associated with root length were mapped on chromosomes 7. The QTL, named qRL7, was located between markers RM3859 and RM214 on chromosome 7 and explained 18.14–18.36% of the total phenotypic variance evaluated across two years. Fine mapping of qRL7 using eight BC₃F₃ recombinant lines mapped the QTL to between markers InDel11 and InDel17, which delimit a 657.35 kb interval in the reference cultivar Nipponbare. To determine the genotype classes for the target QTL in these BC₃F₃ recombinants, the root lengths of their BC₃F₄ progeny were investigated, and the result showed that qRL7 plays a crucial role in root length. The results of this study will increase our understanding of the genetic factors controlling root architecture, which will help rice breeders to breed varieties with deep, strong and vigorous root systems.     

Genetic analysis of methionine content in indica-japonica hybrid rice (Oryza sativa L.) at different grain developmental stages

Genetics of methionine content in indica-japonica hybrid rice (Oryza sativa L.) was studied in 35 F₁ hybrids derived from crossing 7 male-sterile indica rice cultivars with 5 restorer japonica rice cultivars. Two genetic models and their corresponding statistical methods for quantitative traits of triploid endosperm in cereal crops were used for the analysis. One is the unconditional model, which refers to the analysis of cumulative measurements along the developmental stages, while another is the conditional model, which relates to analysis throughout the developmental stages. Results showed that methionine content of indica-japonica hybrid rice was controlled by expression of triploid endosperm nuclear genes, cytoplasm genes, diploid maternal plant nuclear genes, and their genotype-environment interaction effects. Dominant effects were important at the first three developmental stages, while additive effects were important at the next two stages of grain development under both unconditional and conditional analyses. With regard to the components of heritability, maternal and cytoplasm general heritabilities and their environmental interaction heritabilities were important. It was suggested that enhancing methionine content could be more efficient when selection is based on maternal plants in early breeding generations.     

Cause and Consequence in Maize Planting Dates in Germany

An important part of agricultural adaptation is the timing of crop sowing dates, affecting yields and the level of risk incurred during a particular season. Cold stress is especially relevant in maize, Zea mays L., so that the timing of planting in the spring is a tactical response to short‐term weather, but is also subject to strategic planning with regard to longer‐term climate. Both factors compare the potential implications of cold stress to the additional yield obtainable through earlier planting. New cultivars suited to growing conditions in Europe and generally increasing spring temperatures have enabled earlier planting, but it is still dependent on short‐term weather during the planting period. In the context of field‐level decision‐making, a panel regression is used to estimate the relationship between weekly local temperature and precipitation and planting dates at specific sites throughout Germany. Next, localised weather data and planting behaviour are linked to yields at the district (Landkreis) level to show the effects of planting date on yield. Based on these relationships optimal planting dates are explored with some associated costs and benefits. Results show a trend towards earlier planting that follows observed increasing spring temperatures and the availability of more cold‐tolerant cultivars but this advance is buffered by the increasing severity of minimum temperatures during a critical period. Earlier planting potentially increases yield but this is offset by additional management costs and risk. A robust and simple depiction of farmer behaviour in climatic, technological and economic context can help to understand trends in crop management and productivity that effect agricultural landscapes.     

Inheritance of time to flowering in cowpea (<Emphasis Type="Italic">Vigna unguiculata</Emphasis> (L.) Walp.)

Time to flowering and maturity is an important adaptive feature in annual crops, including cowpeas (Vigna unguiculata (L.) Walp.). In West and Central Africa, photoperiod is the most important environmental variable affecting time to flowering in cowpea. The inheritance of time from sowing to flowering (f) in cowpeas was studied by crossing a photoperiod-sensitive genotype Kanannnado to a photoperiod-insensitive variety IT97D-941-1. Sufficient seed of F₁, F₂, F₃ and backcross populations were generated. The parental, F₁, F₂, F₃ and the backcross populations were screened for f under long natural days (mean daylength 13.4 h per day) in the field and the parents, F₁, F₂ and backcross populations under short day (10 h per day) conditions. The result of the screening showed that photoperiod in the field was long enough to delay flowering of photoperiod-sensitive genotypes. Photoperiod-sensitivity was found to be partially dominant to insensitivity. Frequency distribution of the trait in the various populations indicated quantitative inheritance. Additive (d) and additive × dominance (j) interactions were the most important gene actions conditioning time to flowering. A narrow sense heritability of 86% was estimated for this trait. This will result in 26 days gain in time to flowering with 5% selection intensity from the F₂ to F₃ generation. At least seven major gene pairs, with an average delay of 6 days each, were estimated to control time to flowering in this cross.     

Screening techniques and improved biological nitrogen fixation in cool season food legumes

Dinitrogen fixation and legume productivity are greatly influenced through the interactions of legume host, Rhizobium, and the above- and below-ground environment. The benefits of improving legume N₂ fixation include reduced reliance on soil N, leading to more sustainable agricultural systems and reduced requirements for fertilizer N, enhanced residual benefits to subsequent crops, and increased legume crop yields. Most of the gains in N₂ fixation to date have been derived from management of legume cropping systems and through inoculation of legume seed with competitive and symbiotically effective rhizobia. Further gains are possible by developing plant cultivars with tolerance to soil abiotic factors, increased plant yield, and a broader and more effective matching of plant host and rhizobia. Techniques for screening material for superior N₂ fixation and examples of programs to increase fixed N, with attention to the major abiotic stresses, are discussed.