Balance between facilitation and competition determines spatial patterns in a plant population

A considerable challenge in plant ecology is to understand how interactions,such as competition or facilitation,shape the spatial distribution of plants.The‘‘stress gradient hypothesis’’predicts that facilitation and competition will vary inversely across gradients of abiotic stress or consumer pressure.Surprisingly,few previous studies have explored how the balance between facilitation and competition affects spatial patterns along gradients of stress in a plant population based on field experiments.In order to investigate the effects of consumer pressure,facilitation,and competition on the spatial pattern of plant populations,we conducted a restoration succession series field experiment in the Inner Mongolian steppe in which sample sites of graded consumer pressure,specifically grazing stress,were established.We chose to examine the spatial patterns of Leymus chinensis,a dominant species in our experimental site.In order to test the‘‘stress gradient hypothesis,’’we applied the univariate O-ring statistic to analyze local neighborhood density at different spatial scales.We used the pair-correlation function to detect the characteristics of point patterns using complete spatial randomness,the Poisson cluster process,and the nested double-cluster process.We found that the local densities of L.chinensis were higher under high stress than lower stress environments.This demonstrated the‘‘stress gradient hypothesis’’in that facilitation and competition varied inversely across gradients of consumer pressure.However,we found nodifferences in the spatial patterns of L.chinensis based on complete spatial randomness when interactions shifted from facilitation to competition along gradients of consumer pressure.Furthermore,we detected the characteristics of point patterns using the Poisson cluster and nested doublecluster processes.The results showed the spatial patterns of L.chinensis to fit well with the nested double-cluster model under highly stressful conditions,while in lower stress environments they were best approximated by the Thomas process.Our results illustrate that a shift in interactions from facilitation to competition along gradients of consumer pressure can shape spatial patterns and that a combination of the Poisson cluster process and nested doublecluster process can detect spatial pattern characteristics which cannot be detected by complete spatial randomness.     

干旱荒漠区观赏性草坪在园林绿化中的运用与推广

近年来,先后在甘肃武威教师新村、武威铁路阳光住宅小区、张掖铁路康乐住宅小区、永昌发电厂区和生活区、新疆哈密铁路各住宅小区、吐哈油田哈密石油基地建立了6个总面积达30万m2的干旱荒漠区观赏性草坪在园林绿化建设中的示范样板工程,并推动了西北干旱荒漠区观赏草坪业在园林绿化中的快速发展.     

武嘉铁路绿化工程特殊地质条件下提高苗木成活率的施工措施

随着我国近年来对环境保护的重视,在绿化行业中一些新品种和新技术的引进和研发,在施工应运中大大的提高了生产率。本论述阐明了武嘉铁路绿色防护工程所处地段的自然状况的特殊性,针对其特殊性在设计中合理选择和配置苗木,在施工中苗木的处理上如何运用多种措施相结合从而最终达到提高苗木的成活率。     

酸胁迫下紫花苜蓿的生理耐受极限

用沙培结合营养液培养的方法，以紫花苜蓿WL525为实验材料，通过模拟典型南方酸性土壤中的酸胁迫因子，对苜蓿幼苗进行不同酸度环境下的酸胁迫实验，探讨紫花苜蓿对于各酸度的生理耐受极限。研究结果表明：pH为4的环境酸度是苜蓿幼苗能够耐受的生理极限。在此酸度环境下，植株的根系活力，光能转化效率，尚能维持在与对照差异不大的水平上，可以维持正常生长。在撤除胁迫后生理指标恢复到较好的生长状态。当环境pH值低于该水平时，植株不能耐受。随环境pH值的降低，叶绿素浓度、光合转化效率和根系活力显著下降。     

植物胁迫“印记”形成的分子机制及脱落酸和水杨酸的调控作用

“植物胁迫‘印记’形成的分子机制及脱落酸和水杨酸的调控作用”是沈阳师范大学化学与生命科学学院李雪梅教授主持的国家自然科学基金面上项目（批准号：30870205）,资助经费33万元，起止时间为2009年1月至2011年12月。     

不同品种白刺幼苗对盐分胁迫的适应性研究

对不同品种白刺幼苗的耐盐能力进行研究。结果表明,不同品种白刺幼苗在同样浓度盐分胁迫下,齿叶白刺的高增长率具有明显的优势,小果白刺在新枝以及地径增长方面具有明显的优势,尤其是地径增长受盐分胁迫的影响程度较小;同一品种白刺幼苗在盐浓度逐渐增加的过程中,小果白刺高、新枝、地径增长率受胁迫影响的程度均最小。     

Characterization of Arabidopsis calreticulin mutants in response to calcium and salinity stresses

As an important calcium-binding protein, calreticulin plays an important role in regulating calcium homeostasis in endoplasmic reticulum （ER） of plants. Here, we identified three loss-of-function mutants of calreticulin genes in Arabidopsis to demonstrate the function of calreticulin in response to calcium and salinity stresses. There are three genes encoding calreticulin in Arabidopsis, and they are named AtCRT1, 2, and 3, respectively. We found that both single mutant of crt3 and double mutant of crtl crt2 were more sensitive to low calcium environment than wild-type Arabidopsis. Moreover, crt3 mutant showed more sensitivity to salt treatment at germination stage, but tolerance to salt stress at later stage compared with wild-type plant. However, there was no obvious growth difference in the mutant crtl and crt2 compared with wild-type Arabidopsis under calcium and salt stresses. These results suggest that calreticulin functions in plant responses to calcium and salt stresses.     

线虫对环境胁迫适应机制

土壤线虫是土壤动物中最丰富的组分,在土壤有机质的分解、植物营养的矿化及养分循环中起着重要作用,目前已被广泛地应用于农林生态系统及土壤健康的指示研究中.土壤线虫的生存和适应能力极强,广泛存在于各种生境中.在各类土壤及任何气候条件下都可以找到线虫,它们甚至能生活在极限环境介质中.参23.     

我国东部夏季北旱南涝的成因,展望和对策

近10余年来在全球增暖、中高纬降水普遍增多时期，我国东部却是夏季风雨带南移，频繁出现北旱南涝、黄河断流，达到近千年来罕见的程度。笔者的研究表明，这主要起因于人为因素。首先是由于近年来我国东部工业迅猛发展（尤其是乡镇企业），用煤量剧增，大量排放的SO2和烟尘减弱     

有毒植物胁迫与农耕兴起

目的 为了更好地认识农耕兴起的原因,从现代生态学和毒理学的角度研究有毒植物与人类之间的关系.方法 对关于有毒植物的史料记栽整理研究,结合农耕的发展进程,分析了二者之间的联系.结果 表明有毒植物的毒性方程抑制了脊椎动物的取食行为,因此改变了它们的食物构成,而且植物化感毒性对稳定的农耕起到了推动作用.结论 有毒植物胁迫是农耕兴起的诸多因素之一,特别是从有毒植物到食物作用的进化,从植物化感毒性对农耕稳定的作用等方面促使人类作出农耕的选择.