人力资本效能的彰显:激励与约束

人力资本是生产要素中最活跃和最特殊的要素，它的激励与约束问题极为精巧、复杂．本文通过对人力资本激励与约束问题的考察，结合我国体制内企业运营的实践，初步探讨了人力资本激励与约束的机制．     

物种多度对数正态分布模型的一种数值计算方法

物种多度分布格局是生物多样性研究的重要内容．本文针对物种多度分布的对数正态模型计算方法的缺陷,首次提出应用遗传算法计算对数正态模型参数,并与前人计算方法进行了比较,证明遗传算法具有较强的数值计算能力,对生态学中诸多非线性曲线的参数估计具有普遍意义．     

用遗传算法优化工业污染源布局

工业污染源的优化布局是复杂的以偏微分方程为约束条件的控制问题。遗传算法是一种近年发展起来并广泛应用于多个领域优化问题的最优化方法。引入罚函数来处理环境不等式约束，建立了适当的编码方式和适应度函数，应用遗传算法以求解优化布局问题，并进行了数值试验。数值试验结果表明，遗传算法可以有效地用于求解工业污染源的优化布局问题，而且该方法鲁棒性好，适用于任意的目标函数和空气污染模式，天然适合于并行计算，有很好的应用前景。     

目标树初期经营对马尾松人工林灌草层生态位的影响

目标树经营是近自然森林经营的一项主要措施，研究马尾松人工林灌草层生态位对目标树经营具有指导作用，可为马尾松人工林的可持续经营提供参考意见.以华蓥市天池林场36年生马尾松人工林为研究对象，设置3种目标树密度(100、150、200株/hm²)，辅之对照林分(CK)，分析目标树经营3年后对马尾松人工林林下灌木和草本层生态位宽度和生态位重叠度的影响.结果表明：(1)与CK相比，不同密度目标树经营后的灌草层物种丰富度指数均显著增大；(2)实施3种不同密度的目标树经营后，林下灌草层优势种不同，但优势种之间生态位重叠；(3)目标树经营后灌木层的优势种为樟(Cinnamomum camphora)、枹栎(Quercus serrata)、木姜子(Litsea pungens)、毛桐(Mallotus barbatus)；草本层的优势种为皱叶狗尾草(Setaria plicata)、黑足鳞毛蕨(Dryopteris fuscipes)、芒(Miscanthus sinensis)、芒萁(Dicranopteris dichotoma)，这些物种占据群落重要地位并能充分利用该生态系...     

目标树初期经营对杉木人工林林下植物多样性和土壤理化性质的影响

目标树经营为近自然林业的重要手段,研究其林下植物多样性与土壤理化性质对目标树经营密度的响应机制对于人工林经营有着重要的参考意义.以宜宾市高县月江国有林场杉木人工林为研究对象,分析3种不同目标树密度(100株/hm2、150株/hm2、200株/hm2)在经营1年后的林下植物多样性和土壤理化性质的变化情况.结果显示:(1...     

麻疯树AFLP体系的建立与优化

为了建立麻疯树AFLP(Amplified fragment length polymorphism)反应体系及筛选出扩增条带丰富的引物,以17份来自不同地方的麻疯树的幼嫩叶片为试材,对影响AFLP分析的关键因素包括DNA的提取质量和浓度、MseⅠ/EcoRⅠ酶切反应时间和浓度、银染方法等进行了研究,从64对引物组合中筛选出适合麻疯树的引物.结果表明,改良的CTAB方法提取的DNA质量比较好.建立了一种适于麻疯树AFLP的优化体系:模板DNA的用量为400 ng,酶切反应时间为3 h,筛选出T8对适合麻疯树扩增条带多、多态性强的引物.最终建立了适用于麻疯树的AFLP反应体系,并筛选出适合麻疯树的引物,为今后利用AFLP标记技术进行麻疯树的遗传多样性分析提供了标准化程序.图5表2参15     

湖南耐寒桉树优良单株组培研究

本研究以湖南省林业技术推广总站在湖南选育的17个耐寒桉树优良单株为试验材料,进行组培繁殖,有14个优良单株成功地诱导出了愈伤组织或芽。结果表明,以一年生扦插苗的当年生嫩枝作为外植体来源,污染率低且愈伤组织和芽的诱导率高;0.25％氯化汞消毒15—20分钟,可将污染率控制在70％以下,且对外植体的损害最小;按树最佳的诱导培养基为:1/2MS+BA_(1.0)+IBA_(0.25),最佳的继代培基为:MS+BA_(1.0)+KT_(1.0)+VB2_(10)。     

酶联免疫吸附法测定麻疯树核糖体失活蛋白

建立了一种检测麻疯树核糖体失活蛋白(Curcin)的简便、快速的酶联免疫吸附测定法(ELISA).ELISA条件优化试验结果显示:最佳条件为costar酶标板在紫外线下照射45 min后进行包被;抗原最适稀释度为1:640倍(2.5μg/mL);curcin抗血清最适稀释度为1:12 800倍;2%封闭用山羊血清封闭120 min;二抗最适稀释度为1:5 000倍.在此试验条件下检测curcin含量,得到回归方程y=31.722x+106.88,相关系数R2=0.993 3.Curcin浓度在0.08～11μg/mL之间,曲线呈良好的线性关系.本方法的最低检测限为0.08μg/mL.高、中、低3个浓度的添加回收率分别为95.56%、102.27%、98.40%,平均回收率为98.74%.板内和板间的平均变异系数分别为4.78%和6.71%.Curcin抗血清与2种大戟科同类蛋白均无交叉反应.利用本方法成功检测了麻疯树种仁及脱毒饼粕中的curcin含量.     

栘依树抗氧化剂对香烟烟气自由基及人淋巴细胞姐妹染色单体交换率的影响

采用电子顺磁共振法研究了栘依树抗氧化剂对香烟烟气自由基含量的影响,并比较了不同自由基含量的香烟烟气冷凝物(CSC)对人淋巴细胞姐妹染色单体的损伤情况.在香烟滤嘴中注入50μL0.2%的栘依树抗氧化剂溶液后,香烟烟气中气相、粒相自由基含量分别降低40.2%和28.3%,平均降低39.6%;中高剂量的实验烟(添加栘依树),与对照烟(不加栘依树)相比,人淋巴细胞姐妹染色单体交换率显著降低(t＞t0．05),其中中剂量烟降低幅度更大;低剂量实验烟与对照烟相比,姐妹染色单体交换率也有降低趋势,但差异不显著(t相似文献   

麻疯树胚乳愈伤组织诱导及其污染消除

经过比较分析各种消毒方法,获得了较为理想的麻疯树(Jatrophacurcas)胚乳愈伤组织,并动态观察其类型、形态特征、增殖速率和形态发生能力,为麻疯树胚乳植株再生及愈伤组织和细胞培养生产药用成分奠定了基础.以麻疯树成熟胚乳为外植体进行愈伤组织的诱导,测试0.4mg/L的分裂素(BA、KT与TDZ)与2.0mg/L的生长素(IAA、IBA、NAA与2,4D)搭配组合的诱导效果.结果表明,对胚乳愈伤诱导效果而言,2.0mg/L的2,4D效果最好,NAA的效果次之,IBA又次之,IAA的效果最差.BA和KT诱导效果差异不显著,TDZ的添加可促进胚乳愈伤组织的诱导.选择适宜的消毒剂(种类、浓度)和消毒(处理)时间对胚乳外植体的接种成功具有至关重要的作用.在本试验所采取的灭菌方式中,用70%酒精处理30s,然后用10%NaClO处理25min,灭菌效果最佳,同时对胚乳外植体的生长影响最小.图3表1参23     

Predicting long-term development of abandoned subalpine conifer forests in the Swiss National Park

In the past 35 years, various kinds of dynamic models have been used to study vegetation development during primary or secondary succession. Typically, one specific model or models with the same conceptual background were employed. It remains largely unknown to what extent such model-based findings, e.g., on the speed of succession, depend on the specific model approach.To address this issue, we estimated the time elapsing during secondary succession in subalpine conifer forests of the Swiss National Park using three models of different conceptual background: (i) a forest gap model, (ii) a Markov chain model, and (iii) a minimum spanning tree model.Starting from a 95- to 125-year-old mountain pine (Pinus montana Miller) forest, all three models predicted a similar successional development. Even though the forest gap model and the Markov chain model are based on totally different approaches and were calibrated using different data sets, they both forecasted that it would take 500–550 years to reach a late-successional forest stage. The minimum spanning tree model, which only reveals a certain number of time steps yielding a minimum time estimate, showed a development of tree density (stems/ha) that was similar to the results of the forest gap model, but a strict quantitative comparison is not feasible.Our study shows that modeling forest development using three different approaches is quite powerful to obtain a robust estimate of the speed of forest succession. In our case, this estimate is higher than what has been suggested in previous studies that investigated secondary forest succession. The use of several approaches allows for a more comprehensive analysis in terms of variables covered (e.g., relative forest cover in the Markov approach vs. stand-scale species composition in the forest gap model). We recommend that in studies focusing on the speed of succession, several models should be employed simultaneously to identify inconsistencies in our knowledge and to increase confidence in the results.     

Estimating the removal of atmospheric particulate pollution by the urban tree canopy in Beijing北大核心CSCD

Urban green space, particularly the tree canopy, plays an important role in potential mitigation against atmospheric particulate pollution and protecting human health. In this study, current and future air particulate matter [including total suspended particulate (TSP), particulate matter 10 (PM10), and particulate matter 2.5 (PM2.5)] removal by the urban tree canopy of Beijing was estimated. A modeling approach was used based on the distributed measurement evaluation and a modified version. The urban tree canopy of Beijing, including mostly Platycladus sp., Pinus sp., Quercus sp., Robinia pseudoacacia, and economic forests, currently removes about 8.33 million kg/a air particulates, in which TSP accounted for 4.51 million kg/a, PM10 accounted for 2.74 million kg/a, and PM2.5 accounted for 1.08 million kg/a. The study on the removal of air particulates by different aged tree canopies showed that in coniferous trees, the ability to capture air particulates changed in the order of mature and over-mature > near-mature forest > young forest; in broadleaf forest, the ability changed in the order of near-mature forest > mature and over-mature > young forest. For total particulate matter, the biggest contribution was coarse particulates (60.74%); the contribution rate of fine particulates was different owing to different tree species groups. The results suggested that the ability of different trees to capture particles and age of forests varied widely and that suitable trees should be chosen to enhance pollution mitigation for city greening. © 2018 Science Press. All rights reserved.     

Nutrient fluxes at the landscape level and the R* rule

Nutrient cycling in terrestrial ecosystems involves not only the vertical recycling of nutrients at specific locations in space, but also biologically driven horizontal fluxes between different areas of the landscape. This latter process can result in net accumulation of nutrients in some places and net losses in others. We examined the effects of such nutrient-concentrating fluxes on the R* rule, which predicts that the species that can survive in steady state at the lowest level of limiting resource, R*, can exclude all competing species. To study the R* rule in this context, we used a literature model of plant growth and nutrient cycling in which both nutrients and light may limit growth, with plants allocating carbon and nutrients between foliage and roots according to different strategies. We incorporated the assumption that biological processes may concentrate nutrients in some parts of the landscape. We assumed further that these processes draw nutrients from outside the zone of local recycling at a rate proportional to the local biomass density. Analysis showed that at sites where there is a sufficient biomass-dependent accumulation of nutrients, the plant species with the highest biomass production rates (roughly corresponding to the best competitors) do not reduce locally available nutrients to a minimum concentration level (that is, minimum R*), as expected from the R* rule, but instead maximize local nutrient concentration. These new results require broadening of our understanding of the relationships between nutrients and vegetation competition on the landscape level. The R* rule is replaced by a more complex criterion that varies across a landscape and reduces to the R* rule only under certain limiting conditions.     

Constraints on tree seedling establishment in montane grasslands of the Valles Caldera, New Mexico

Montane and subalpine grasslands are prominent, but poorly understood, features of the Rocky Mountains. These communities frequently occur below reversed tree lines on valley floors, where nightly cold air accumulation is spatially coupled with fine soil texture. We used field experiments to assess the roles of minimum temperature, soil texture, grass competition, and ungulate browsing on the growth, photosynthetic performance, and survival of transplanted ponderosa pine (Pinus ponderosa) seedlings at 32 sites straddling such reversed tree lines in the Valles Caldera National Preserve (VCNP) of the Jemez Mountains, New Mexico (USA). Seedling growth increased most strongly with increasing nighttime minimum temperatures away from the valley bottoms; seedlings experiencing the coldest temperatures on the caldera floor exhibited stunted needles and often no measurable height growth. Based on the chlorophyll fluorescence ratios PhiPSII and Fv/Fm, we found that low minimum temperatures, low soil moisture, and fine soil texture all contributed to photoinhibition. Neighboring herbs had only minor negative effects on seedlings. We found no effect of ungulates, but golden-mantled ground squirrels (Spermophilus lateralis) caused substantial seedling mortality. Second-year seedling survival was highest on sandy soils, and third-year survival was highest at sites with higher minimum temperatures. We conclude that differential tree seedling establishment driven by low minimum temperatures in the valley bottoms is the primary factor maintaining montane grasslands of the VCNP, although this process probably operated historically in combination with frequent surface fire to set the position of the tree line ecotone. As at alpine tree lines, reversed tree lines bordering montane and subalpine grasslands can represent temperature-sensitive boundaries of the tree life form.     

New multidimensional functional diversity indices for a multifaceted framework in functional ecology

Functional diversity is increasingly identified as an important driver of ecosystem functioning. Various indices have been proposed to measure the functional diversity of a community, but there is still no consensus on which are most suitable. Indeed, none of the existing indices meets all the criteria required for general use. The main criteria are that they must be designed to deal with several traits, take into account abundances, and measure all the facets of functional diversity. Here we propose three indices to quantify each facet of functional diversity for a community with species distributed in a multidimensional functional space: functional richness (volume of the functional space occupied by the community), functional evenness (regularity of the distribution of abundance in this volume), and functional divergence (divergence in the distribution of abundance in this volume). Functional richness is estimated using the existing convex hull volume index. The new functional evenness index is based on the minimum spanning tree which links all the species in the multidimensional functional space. Then this new index quantifies the regularity with which species abundances are distributed along the spanning tree. Functional divergence is measured using a novel index which quantifies how species diverge in their distances (weighted by their abundance) from the center of gravity in the functional space. We show that none of the indices meets all the criteria required for a functional diversity index, but instead we show that the set of three complementary indices meets these criteria. Through simulations of artificial data sets, we demonstrate that functional divergence and functional evenness are independent of species richness and that the three functional diversity indices are independent of each other. Overall, our study suggests that decomposition of functional diversity into its three primary components provides a meaningful framework for its quantification and for the classification of existing functional diversity indices. This decomposition has the potential to shed light on the role of biodiversity on ecosystem functioning and on the influence of biotic and abiotic filters on the structure of species communities. Finally, we propose a general framework for applying these three functional diversity indices.     

Using T-RFLP technology to analyze bacterial diversity in the rhizospheric soils of tea tree at different ages北大核心CSCD

The rhizospheric soils of Tieguanyin at different ages were used as the study materials, and terminal-restriction fragment length polymorphism (T-RFLP) was used to analyze the changes in bacterial diversity. The results showed that the number of T-RFs, Simpson index, and Shannon index decreased significantly with the age of the tea tree. Results of correlation analysis showed that 9 T-RFs from the bacterial community were significantly and positively correlated with the age of the tea tree, and included 34 species of microbes belonging to 10 classes. The 34 microbes were divided into 6 types according to their functional attributes, and included pathogenic bacteria, bacteria that improved soil texture or inhibited pathogenic bacteria, and bacteria associated with the carbon, nitrogen, or sulfur cycles, in which the percentage of pathogenic bacteria was 58.82%. Seventeen T-RFs were significantly and negatively correlated with the age of the tea tree, and included 38 species of bacteria belonging to 12 classes. The 38 bacterial species were divided into 5 types according to their functional attributes, and included pathogenic bacteria, bacteria that improved soil quality or inhibited pathogenic bacteria, and bacteria associated with the carbon cycle or nitrogen cycle, in which all the others, barring the pathogenic bacteria, accounted for 78.95% of the bacterial population. In brief, the diversity and function of bacteria in the rhizospheric soil of tea tree changed significantly with the age of the tea tree, which provides a theoretical basis for studying the interactions of bacterial communities. © 2018 Science Press. All rights reserved.     

提高碳汇潜力：量化树种和造林模式对碳储量的影响

全球气候变化背景下,造林再造林固定的碳可以抵消温室气体减限排量。通过造林再造林增加森林面积可以增加林业碳汇,在土地面积有限的情况下,提高造林质量——在有限的造林面积上固定更多的碳是十分必要的。树种和造林模式的选择是增加森林生态系统碳汇的重要管理决策。文章综述了树种和造林模式对生态系统的碳储量的影响。树种从生物量的积累,凋落物和土壤碳储存,以及木材密度、碳贮存量等几个方面探讨其对生态系统碳库的影响。混交林能充分利用立地条件、改善树木营养状况,并且可以减少病虫害和森林火灾。同时分析了我国在森林经营方面存在的问题和改善途径,以期为该领域的研究提供参考。     

Trees and rural households’ adaptation to local environmental change in the central highlands of Ethiopia

This study assesses the role of trees in adaptation strategies of rural households to local environmental change in the central highlands of Ethiopia. Change in tree cover was assessed by producing Land Use and Land Cover (LULC) maps using satellite remote sensing images, and household survey was conducted to generate socioeconomic data. The results show that tree cover has increased over the last 30 years, mostly in the form of eucalyptus woodlots around homesteads. Eucalyptus reportedly helps households pass through livelihood shocks and provide protection against negative effects of climate change and variability. Despite some concerns on the part of local agricultural experts that planting eucalyptus may affect future food production, farmers are converting their croplands into eucalyptus woodlots. We conclude that land use planning and proper allocation of land resource is important to improve local livelihoods while also supporting adaptation of communities to local environmental change in general and climate change in particular.     

Efficiency and robustness of ant colony transportation networks

Efficient and robust transportation networks are key to the effectiveness of many natural systems. In polydomous ant colonies, which consist of two or more spatially separated but socially connected nests, resources must be transported between nests. In this study, we analyse the network structure of the inter-nest trails formed by natural polydomous ant colonies. In contrast to previous laboratory studies, the natural colonies in our study do not form minimum spanning tree networks. Instead the networks contain extra connections, suggesting that in natural colonies, robustness may be an important factor in network construction. Spatial analysis shows that nests are randomly distributed within the colony boundary and we find nests are most likely to connect to their nearest neighbours. However, the network structure is not entirely determined by spatial associations. By showing that the networks do not minimise total trail length and are not determined only by spatial associations, the results suggest that the inter-nest networks produced by ant colonies are influenced by previously unconsidered factors. We show that the transportation networks of polydomous ant colonies balance trail costs with the construction of networks that enable efficient transportation of resources. These networks therefore provide excellent examples of effective biological transport networks which may provide insight into the design and management of transportation systems.     

决策树法在投标决策中的应用

为了提高施工企业的中标概率,获取更多的利润,减少决策失误.本文对决策树法的基本理论、适用条件、绘制方法及选取最佳方案进行了探索.