人民币汇率变动对就业影响的动态CGE研究

通过引入资本累积、金融资本累积以及劳动力市场的调整3种跨期链接将可计算一般均衡模型动态化,研究人民币汇率变动对中国就业的冲击影响研究结果表明：人民币升值将导致中国劳动力成本提高,使得很多劳动密集型企业丧失产品价格优势,进而使得失业人口增加;人民币升值对不同行业的影响各异,将导致劳动密集型行业和原材料出口型行业的就业形势严重恶化,人民币升值对以原料进口的行业具有正向作用,服务业也从人民币升值中受益,人民币升值对我国第一产业就业影响较为稳定.     

我国农户生猪散养与生猪及猪肉市场价格波动

生猪农户散养资源投入机会成本极低,因此其生产目的主要是自给性要素利用而非盈利。这种饲养方式加剧了供给对价格反应的迟滞性和价格波动幅度。     

Assessment of maximum daily trunk shrinkage signal intensity threshold values for deficit irrigation in lemon trees

The response of adult Fino lemon trees (Citrus limon L. Burm. fil.) on sour orange (Citrus aurantium L.) to an irrigation schedule based exclusively on maximum daily trunk shrinkage (MDS) measurements was studied during the 2005-2006 and 2006-2007 seasons. Plants irrigated above their crop water requirements (T0 treatment) were compared with plants under deficit irrigation, whereby the MDS signal intensity (actual MDS/reference MDS) threshold values were maintained at around 1.15 (T1 treatment), 1.25 (T2 treatment) and 1.35 (T3 treatment). Cumulative crop evapotranspiration (ETc) values reached 536.9 and 719.4 mm during the first and the second season, respectively, and the cumulative amounts of applied water in the deficit irrigation treatments were 662.4 mm (T1, 2006-2007 season), 396.3 mm (T2, 2005-2006 season), 554.0 mm (T2, 2006-2007 season) and 220.3 mm (T3, 2005-2006 season), which generated mild, moderate and severe water stress in T1, T2 and T3 plants, respectively. Results indicated that measurements of MDS are suitable for scheduling irrigation, except for rainy periods of low evaporative demand. Therefore, to improve the precision of irrigation management, some changes in the irrigation protocol should be introduced, for instance, using higher MDS signal intensity threshold values and/or a lower irrigation frequency. According to market demand, lemon fruits were harvested on two occasions, showing no effect of irrigation treatment on total yield and total number of fruits per tree. T2 and T3 treatments resulted in a lower yield and number of fruits per tree at the first harvest and modified fruit characteristics. In contrast, the yield at first harvest and number of fruits per tree was not affected in T1 (92% ETc) plants and fruit characteristics were hardly impaired.     

Litter, warming and plants affect respiration and allocation of soil microbial and plant C, N and P in arctic mesocosms

In a mesocosm experiment, we studied decomposition rates as CO₂ efflux and changes in plant mass, nutrient accumulation and soil pools of nitrogen (N) and phosphorus (P), in soils from a sub-arctic heath. The soil was incubated at 10 °C and 12 °C, with or without leaf litter and with or without plants present. The purpose of the experiment was to analyse decomposition and nutrient transformations under simulated, realistic conditions in a future warmer Arctic.Both temperature enhancement and litter addition increased respiration rates. Temperature enhancement and surprisingly also litter addition decreased microbial biomass carbon (C) content, resulting in a pronounced increase of specific respiration. Microbial P content increased progressively with temperature enhancement and litter addition, concomitant with increasing P mineralisation, whereas microbial N increased only in the litter treatment, at the same time as net N mineralisation decreased. In contrast, microbial biomass N decreased as temperature increased, resulting in a high mobilisation of inorganic N.Plant responses were closely coupled to the balance of microbial mineralisation and immobilisation. Plant growth and N accumulation was low after litter addition because of high N immobilisation in microbes and low net mineralisation, resulting in plant N limitation. Growth increased in the temperature-enhanced treatments, but was eventually limited by low supply of P, reflected in a low plant P concentration and high N-to-P ratio. Hence, the different microbial responses caused plant N limitation after litter addition and P limitation after temperature enhancement. Although microbial processes determined the main responses in plants, the plants themselves influenced nutrient turnover. With plants present, P mobilisation to the plant plus soil inorganic pools increased significantly, and N mobilisation non-significantly, when litter was added. This was presumably due to increased mineralisation in the rhizosphere, or because the nutrients in addition to being immobilised by microbes also could be absorbed by plants. This suggests that the common method of measuring nutrient mineralisation in soils incubated without plants may underestimate the rates of nutrient mobilisation, which probably contributes to a commonly observed discrepancy of measured lower rates of net nutrient mineralisation than uptake rates in arctic soils.     

黄河源区径流波动变化对气候要素的响应特征

黄河源区径流属典型的寒区径流,降水、冰雪冻土融水等共同成为径流量的补给来源,径流量的变化同时受到区域内降水量和气温变化的影响。采用互谱分析方法研究表明,黄河源区降水与径流周期波动间的关系明显好于气温与径流之间的关系,降水对径流量的主要周期波动变化有较明显的控制作用。气温虽然对径流量的部分周期波动变化有一定的影响,但明显不如降水的影响。黄河源区径流量的波动变化对区域内生态环境有显著的影响,1980年代后期以来径流大幅下降使与河流水体相连并进行水量交换的湖泊、沼泽湿地疏干退化,生态环境明显恶化。     

Nitrogen waste from rainbow trout (Oncorhynchus mykiss) with particular focus on urea

Particulate and dissolved nitrogen (N) waste components are removed in recirculating aquaculture systems (RAS) using different cleaning technologies, and to dimension and optimize their removal efficiency requires that the expected daily load of the different waste forms can be estimated. Using a laboratory, mass-balance approach, the current study examined the effects of commercially applied feeding levels on the loading of different N waste forms, including daily fluctuations in dissolved total nitrogen (TN), total ammonia nitrogen (TAN), urea-N, and non-characterized, dissolved N deriving from juvenile rainbow trout (Oncorhynchus mykiss). In addition, the study examined whether there was a removal of urea-N across a moving bed biofilter operated as end-of-pipe under commercial conditions. The laboratory, mass-balance study showed that there were no effects of feeding levels (1.3, 1.5 or 1.7% of the biomass per day ) on the excretion of dissolved N components, which constituted the majority of total N waste (>81.6% on average). The excretion of urea-N and non-characterized, dissolved N components constituted 12–13% and 9–11%, respectively of dissolved TN. The excretion of urea-N was largely constant and independent of the daily feeding practice, whereas that of non-characterized N appeared to reflect the daily feeding activity, following the trends in TN and TAN. The time limited feeding regime applied in the laboratory study resulted in a pulse in the excretion of TAN that a biofilter may be unable to fully level out, potentially resulting in unnoticed, critical water quality conditions in intensive RAS during certain times of the day. Particulate N waste constituted a minor fraction of total N waste (<18.4% on average), and the actual loading depended on the digestibility of dietary protein/nitrogen. Results from the commercially operated, nitrifying biofilter showed that urea-N was removed at a rate of 0.014 g N m² day⁻¹. Compared to the removal of TAN (0.208 g N m² day⁻¹), the moving bed biofilter was 1.07 times more active in removing dissolved N than immediately expected when only considering TAN.     

硝基漆模耐温变性的初步研究

涂饰硝基漆的木制品表面漆膜容易开裂,本文探讨了涂料组成与配方、基材树种与切面、涂层厚度以及有无底漆等情况对漆膜耐温变性的影响。结果表明,醇酸树脂与顺酥树脂以4∶1的配比时,漆膜耐温变性好;椴木比松木、径切面比弦切面表面漆膜有较好的耐温变性。     

浅析"八五"以来我国林业经济发展的周期性波动

林业作为国民经济的重要组成部分,在国民经济周期波动的大背景下,林业经济也存在着周期性波动。本文通过对“八五”以来我国林业经济周期问题的初步分析,力图揭示在社会主义市场经济高速发展时期,我国林业经济发展的特点、规律以及引起林业经济周期性波动的内外部动因,并在此基础上提出了有利于我国林业经济稳定发展的政策建议。     

Germination of an obligate seeder (Ulex parviflorus) and consequences for wildfire management

In fire-prone ecosystems, reducing the risk of wildfire is generally attempted through vegetation clearing using controlled fires or, less often, mechanical techniques. Management practices, however, can be poorly efficient when the disturbances they introduce install environmental conditions that are similar to the ones under which the undesirable species evolved. Ulex parviflorus is a Mediterranean obligate seeder with physical dormancy forming large amounts of highly combustible standing necromass. In the present study, combining field and laboratory experiments, we determined the seedling recruitment of this species under different management practices (burning, mechanical clearing, slash/no slash on soil surface), we measured the environmental conditions (temperature, light, and moisture) enforced by these practices and we tested their individual and combined impact on germination in order to determine the most appropriate control method for this species. Germination is low under intact canopies, but it is strongly stimulated by both brush-chipping and fire. This is partly related to the inhibiting effect of the low red:far-red ratio of the light filtered by the canopy which is removed by brush-chipping and fire. The other factor involved is moderate heat, either fire-generated or resulting from solar radiation on bare soil, which breaks seed coat impermeability. Indeed exposing seeds on bare soil in summer resulted in a significant increase in their germination capacity and germination was reduced when the brush chips remained on the soil. Moisture fluctuations did not enhance germination. The summer heat impact affects management practices. When the brush-chipping treatment occurred before summer, the germination flush appeared the following autumn, but when the treatment occurred after summer, the germination flush did not appear until the autumn of the subsequent year, when interspecific competition with regenerating vegetation is likely to be more intense. We demonstrated that brush-chipping, especially when done after summer, is a better technique than fire for controlling U. parviflorus because it creates environmental conditions that are less favourable for its germination. This technique also has the potential to favour late-successional species less vulnerable to fire. By combining fuel reduction and land restoration, this technique is useful to the sustainable management policies that need to be developed.     

国际与国内棉花价格的非线性空间传导研究

随着国内棉花市场开放程度增加,国内外棉花价格联动性增强,明晰国内外棉花价格传递机制尤为重要。采用2007年4月6日至2018年7月6日的周数据,运用MSIH(3)-VAR(P)模型和脉冲响应分析中国棉花期现货市场、国际期货市场之间的相互影响以及非线性空间传导关系。实证结果表明,国际棉花期货市场、中国棉花期现货市场价格波动存在三区制的非线性传导效应,需要重视棉花补贴政策对市场分区带来的影响。中国棉花期现货市场对国际棉花市场波动的响应相对较弱,存在削弱影响的因素,而且受国际棉花期货市场价格的引导;中国棉花期货市场对现货市场的价格有更强的响应,现货市场价格识别期货价格信息能力相对较弱,但趋向于引领期货市场的价格,中国棉花的期货市场仍有待进一步的开发与完善。这些研究结论与构建的非线性分析棉花价格波动模型,可以为政策制定者和棉花产业相关利益群体提供决策参考。