土壤水分对黄土丘陵区演替序列种种间竞争的影响

种间竞争是不同物种为争夺资源发生的相互关系,对群落植被演替、恢复有重要意义。同时水分是黄土丘陵区植物生长的限制因素,该区多物种种间水资源竞争研究较少,为此选取该区6种演替序列种,采用种对试验法研究其对土壤水分变化的竞争响应。结果表明:(1)除狗尾草外,其他5种植物的生长指标和土壤水分变化趋势基本一致,地下部分变化程度大于地上部分。不同植物最适水分条件不同。(2)单位竞争能力与总竞争能力相似地反映植物种间竞争状况。狗尾草和白羊草在中高水竞争力均高于同组的猪毛蒿、达乌里胡枝子,低水反之。铁杆蒿随着水分减少,竞争力低于茭蒿。受水分胁迫时,达乌里胡枝子、白羊草的竞争力茭蒿、铁杆蒿猪毛蒿、狗尾草,即演替后期种竞争能力演替中期演替初期,符合演替生态位理论。竞争的不对称随着环境生产力的增加而降低。随着演替中土壤水分的减少,物种耐水分胁迫的能力逐渐增强,从而促使演替的继续。     

Process studies in aPinus radiata-pasture agroforestry system in a subhumid temperature environment. I. Water use and light interception in the third year

In this study we determined soil moisture storage, evapotranspiration (ET) and light interception in an agroforestry trial consisting of pine trees grown over (1) control (bare ground), (2) ryegrass/clovers (Lolium perene/Trifolium spp.), (3) lucerne (Medicago sativa), and (4) ryegrass only during the third growing season between 1992 and 1993. The results show that:

生态位理论及其测度研究进展

许多学者都试图给生态位下定义 ,但最具代表性的当推Grinnell、Elton和Hutchinson分别给出的“空间生态位”、“功能生态位”和“多维超体积生态位”定义 ;生态位测度包括生态位宽度、生态位重叠、生态位体积及生态位维数等 ,其中生态位宽度和生态位重叠是描述一个物种的生态位以及物种生态位间关系的重要指标 .该文列举并分析了每一个测度公式的优缺点 ,进而优选出适合森林群落的生态位计测公式 .指出利用性竞争的一个必要条件是生态位重叠 ,但重叠并不一定导致竞争 ,竞争是在资源供应不足且生态位重叠条件下形成的 .     

庞泉沟自然保护区优势种种群竞争关系及其动态预测

利用Hegyi单木竞争指数模型对庞泉沟自然保护区优势种群的种内、种间竞争关系进行了定量分析。结果表明:种内和种间竞争强度随着林木径级的增大而逐渐减小,种内竞争较之与其伴生树种间的竞争剧烈。华北落叶松种内、种间竞争强度大小顺序为:种内>云杉>红桦>白桦>关帝柳>花楸>山杨。竞争强度与对象木胸径之间存在显著的幂函数非线性回归关系,回归结果与林分实际相符,从而为庞泉沟自然保护区混交林理论研究和合理经营提供了科学依据。     

窥探我国果农的合作之路

改革开放以来,我国果业迅猛发展,但产销体制很不完善,产品本身不等于商品,更不等于有了稳定畅销的渠道和市场份额。分散的个体果农户面对竞争的市场,犹如汪洋大海中的叶叶扁舟,显得无能为力。果农协会组织和引领分散果农走向市场,作为利益共享、风险共担的非盈利组织形式,在国外已经是成功的经验和模式,应成为我们之鉴。为振兴我国果业,合作化是我国个体果农的必由之路。果农协会应当实行完全民主化运作,避免“权力”的介入而使之变为“半官方化”、“机关化”和“官僚化”。政府应在制订政策条例、协助开拓市场、科技服务等方面发挥其作用。果农的教育和科技水平亟待提高,民主意识亟待培养和增强。政府在这些方面大有可为。     

高校品牌竞争优势及其法则

为增强学校的竞争实力,通过对高教市场特征的分析,阐明新形势下高校品牌竞争优势,并从校长领导、办学特色、品牌营销等方面选择相对竞争优势等策略,提出要以异分性为切入点树品牌形象、借鉴企业化经营管理模式改善学校教育管理的品牌市场竞争法则。     

Leaf-water potential and soil-water depletion of walnut mulched with polyethylene and intercropped with alfalfa in Central Italy

In Italy, new agroforestry cultural models could play an important role in the diffusion of plantation forestry timber species. We studied the stem growth rates and leaf water potentials () of common walnut (Juglans regia L.), and gravimetric soil moisture (_DW) depletion during the third and fourth growing seasons in an agroforestry trial in central Italy. Since the establishment of experimental plots in 1992, walnut was intercropped with alfalfa (Medicago sativa L.), with or without polyethylene (PE) mulching along tree rows. By the end of the study period, the unmulched-intercropped walnut was almost 68% smaller in stem diameter and height than the sole-unmulched control, demonstrating walnuts sensitivity to alfalfa competition. The competitive effect of alfalfa on walnut stem growth was effectively controlled/reduced by PE mulching. Stem growth rates of mulched-intercropped walnut were always lower than the control, but much higher (ca. 235% in stem diameter and height) than those of unmulched-intercropped walnut. The higher field performance of mulched-intercropped walnut compared to the un- mulched-intercropped treatment was associated with higher soil moisture and predawn and midday values during the summers driest periods. The presence of PE mulching was also associated with lower levels of soil moisture during the early and late growing season, but this did not negatively affect walnut and growth rates. These results suggest that in the climatic conditions of central Italy, competition for soil moisture between young common walnut trees and alfalfa can be substantially lowered, but not completely eliminated, by PE mulching.This revised version was published online in November 2005 with corrections to the Cover Date.     

中国稻米出口竞争力状况分析

在分析世界与中国稻米进出口贸易现状的基础上,采用贸易竞争力指数、显示性比较优势指数、国际市场占有率等测定方法,对比分析了世界较大的大米出口国泰国、印度、美国、巴基斯坦和中国的稻米国际竞争力状况,并通过对中美稻谷成本收益比较分析、中泰稻谷品质比较分析及中国稻米的质量安全分析,进一步探析了影响中国稻米出口竞争力的深层次因素;最后提出了加强研究、引进和推广水稻优质品种,提高稻米品质、建立新的水稻质量标准体系和监测体系、扶持龙头企业、推进优质稻米产业化发展、加强水稻流通体制改革、加强水稻生产的基础设施建设和对水稻生产的补贴份额等提高中国稻米出口竞争力的对策和措施。     

从六力互动模型角度分析天润乳业市场战略

以天润乳业为企业战略分析基点,利用六力互动模型分析天润乳业与供方、买方、替代品厂商、互补品厂商、同行业厂商、潜在进入者六种市场利益主体之间结成的动态竞争及合作关系。基于竞合共生的现实基础,分析天润乳业与六种市场利益主体间竞争与合作的前提条件及相互转换关系,为进一步探寻可持续发展之路,提出转变思维定式、坚持差异化战略、优化产品结构的建议。     

曹典球的近代商战、学战思想与实践

根据新发现的史料 ,结合以往的研究文献 ,集中论述曾两任湖南大学校长的曹典球 ( 1877～ 196 0 ) ,对于湖南近代“商战”、“学战”具有系统的思考和实践 ,是一位杰出的先行者