Evolution of leaf-form in land plants linked to atmospheric CO2 decline in the Late Palaeozoic era

The widespread appearance of megaphyll leaves, with their branched veins and planate form, did not occur until the close of the Devonian period at about 360 Myr ago. This happened about 40 Myr after simple leafless vascular plants first colonized the land in the Late Silurian/Early Devonian, but the reason for the slow emergence of this common feature of present-day plants is presently unresolved. Here we show, in a series of quantitative analyses using fossil leaf characters and biophysical principles, that the delay was causally linked with a 90% drop in atmospheric pCO2 during the Late Palaeozoic era. In contrast to simulations for a typical Early Devonian land plant, possessing few stomata on leafless stems, those for a planate leaf with the same stomatal characteristics indicate that it would have suffered lethal overheating, because of greater interception of solar energy and low transpiration. When planate leaves first appeared in the Late Devonian and subsequently diversified in the Carboniferous period, they possessed substantially higher stomatal densities. This observation is consistent with the effects of the pCO2 on stomatal development and suggests that the evolution of planate leaves could only have occurred after an increase in stomatal density, allowing higher transpiration rates that were sufficient to maintain cool and viable leaf temperatures.     

科尔沁沙地典型植被群落土壤水分异质性

半干旱沙区土壤水分对植物的成活与生长具有重要的影响.通过对不同植物种类区土壤水分的调查分析表明, 不同植物种类对土壤水分的影响存在显著差别.沙区地下水位深, 土壤水分主要依靠降雨补充, 固沙植物的生长明显地影响了土壤水分供给量, 乔木林地的土壤水分状况最差,灌木树种对深层土壤水分消耗少. 荒地的土壤水分状况最好.在半干旱沙地建立人工植被过程中, 应依照土壤水分状况配置植物种类.     

超材料在可重构电磁学中的应用与发展

介绍了超材料在微波(0.3~300 GHz)、太赫兹(0.3~100 THz)和近红外频段(100~790 THz)中的可重构电磁学的调控方法和研究现状,并依照功能分类,对在可重构电磁学方面的应用分别做了综合性归纳描述,最后对其在可重构电磁学方向的未来可能的发展趋势做了进一步的展望。     

Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model

The continued increase in the atmospheric concentration of carbon dioxide due to anthropogenic emissions is predicted to lead to significant changes in climate. About half of the current emissions are being absorbed by the ocean and by land ecosystems, but this absorption is sensitive to climate as well as to atmospheric carbon dioxide concentrations, creating a feedback loop. General circulation models have generally excluded the feedback between climate and the biosphere, using static vegetation distributions and CO2 concentrations from simple carbon-cycle models that do not include climate change. Here we present results from a fully coupled, three-dimensional carbon-climate model, indicating that carbon-cycle feedbacks could significantly accelerate climate change over the twenty-first century. We find that under a 'business as usual' scenario, the terrestrial biosphere acts as an overall carbon sink until about 2050, but turns into a source thereafter. By 2100, the ocean uptake rate of 5 Gt C yr(-1) is balanced by the terrestrial carbon source, and atmospheric CO2 concentrations are 250 p.p.m.v. higher in our fully coupled simulation than in uncoupled carbon models, resulting in a global-mean warming of 5.5 K, as compared to 4 K without the carbon-cycle feedback.     

Decadal co-variability of the summer surface air temperature and soil moisture in China under global warming

The self-calibrating Palmer Drought Severity Index (PDSI) is calculated using newly updated ground observations of monthly surface air temperature (SAT) and precipitation in China. The co-variabilities of PDSI and SAT are examined for summer for the period 1961-2004. The results show that there exist decadal climate co-variabilities and strong nonlinear interactions between SAT and soil moisture in many regions of China. Some of the co-variabilities can be linked to global warming. In summer,sig-nificant decadal co-variabilities from cool-wet to warm-dry conditions are found in the east region of Northwest China,North China,and Northeast China. An important finding is that in the west region of Northwest China and Southeast China,pronounced decadal co-variabilities take place from warm-dry to cool-wet conditions. Because significant warming was observed over most areas of the global land surface during the past 20-30 years,the shift to cool-wet conditions is a unique phenomenon which may deserve much scientific attention. The nonlinear interactions between SAT and soil moisture may partly account for the observed decadal co-variabilities. It is shown that anomalies of SAT will greatly affect the climatic co-variabilities,and changes of SAT may bring notable influence on the PDSI in China. These results provide observational evidence for increasing risks of decadal drought and wet-ness as anthropogenic global warming progresses.     

The response of clonai growth of Hippophae rhamniodes L.subsp sinensis to the availability of soil moisture in Mu Us sand land

通过生物量测定和跟踪挖掘法,研究了毛乌素沙地中国沙棘克隆种群生长特征和形态特征对土壤水分条件的可塑性反应.结果表明:低水分条件下,植株个体和种群都较小,子株数量、萌蘖根条数和分枝级数较少,而隔离区较长,种群趋向于游击型;高水分条件下,植株个体和种群都较大,子株数量、萌蘖根条数和分枝级数较多,而隔离区较短,种群趋向于集团型.在生物量分配方面,低水分条件下,枝条、叶片、根系和地上生物量分配比例较大;高水分条件下,树干、萌蘖根和地下生物量分配比例较大.土壤水分条件差异引起中国沙棘个体大小和种群大小的分化,进而导致了种群适合度的差异.     

河北省人口增长与土地资源及粮食供求关系的研究

分析了河北的人口现状、特．点及预测，论述了人口、土地与粮食供求之间的矛盾关系，指出人口压力是土地退化的根本原因．最后提出了解决人口、土地、粮食之间矛盾的建设性对策．     

国际经济格局趋势下的中国普通劳动者权益保护问题研究

多年来,中国被称为世界工厂。然而中国的主要出口商品都是一些中低端产品,制造业的技术含量普遍较低,其竞争力建立在廉价的劳动力成本之上,与此对应的是中国普通劳动者权益福利的丧失。中国人口基数巨大,劳动力市场供大于求。因此,提高普通劳动者权益不能只靠单纯的行政措施,而要顺应国际经济发展的大趋势,建立层次合理的产业结构。通过产业结构调整来增加就业岗位,吸纳劳动力,依靠市场的力量提高普通劳动者的福利。     

接触式散料测水仪在测量烧结混合料水分中的应用

接触式散料测水仪经几年的使用达到了测水仪准确度高，绝对误差长期稳定在≤0.3％；它能在高粉尘、高蒸汽、高温和物料运动条件下在线检测；它对提高烧结矿产量、质量、降低产生成本和提高生产管理水平是非常有益的。     

接触式散料测水仪在测量烧结混合料水分中的应用

接触式散料测水仪经几年的使用达到了测水仪准确度高,绝对误差长期稳定在≤0.3%;它能在高粉尘、高蒸汽、高温和物料运动条件下在线检测;它对提高烧结矿产量、质量、降低产生成本和提高生产管理水平是非常有益的.     

回到小说本身--90年代小说叙事的个人化趋向

本文以小说的本来意义为理论基点,从文学自身发展和外部因素促发两个方面探讨90年代小说叙事的个人化趋向,指出小说发展的一种路向一个人化叙事。     

遥感技术和SEBAL模型在干旱区腾发量估算中的应用

陆地表面的腾发量分布具有很大的空间变异性,而传统方法只能进行点上的计算。为反映表面腾发量的空间特征,引入遥感技术和SEBAL(surface energy balance algorithm for land)模型。遥感技术能够方便、快捷地获取地面信息,而SEBAL模型则利用Landsat TM/ETM影像获取的遥感信息计算区域腾发量。该文在SEBAL模型的基础上,针对具体研究区域的客观情况进行参数改进,在ERDAS软件支持下,计算获得了研究区域地面反照率、地面温度以及各能量分量的空间分布。结果分析表明,参数改进后模型计算过程简捷,结果基本合理,具有广阔的应用前景,尤其对于缺乏观测资料的地区,更是一种行之有效的方法。     

有限集上二元关系传递闭包的一种矩阵求法

利用关系矩阵给出有限集上传递闭包的一种求法,使得求传递闭包变得既直观又迅速。该方法简便、实用、易于操作。     

土地使用权评估方法的应用研究

土地使用权评估是资产评估实务操作的难题,其方法的研究一直是热点问题之一,本文将近几年有关研究成果加以整理汇集,以供评估、财务管理工作人员和研究者参考。     

灰色关联度分析法在土地评价中的应用

作者选取四川省"金土工程"数据库中的原始数据作为研究基础,通过应用灰色系统理论的关联分析方法,以坡度、地面岩石露头、灌溉保证、排水条件、土壤构型、有效土层厚度、土壤酸碱度和土壤有机质作为与水稻平均产量相关的因子进行多因素关联分析,结果显示该区域排水条件与其产量具有最大的关联度.这说明在四川地区水稻地排水条件的优劣最大程度地决定着水稻的产量.通过各要素权重值的计算得到该地区土地等级划分范围.表明在土地评价中运用灰色关联度分析方法可减少人为的经验误差,同时该方法简单易行,结果可信度高.     

蒙城县农村饮水安全工程建设的技术要点

蒙城县是安徽省水源性传染病和地方病发率较高的县,境内高氟水、苦咸水、污染水等饮水安全问题比较严重;在进行农村饮水安全工程建设中,水源确定是其中的重要基础。该文结合饮水不安全问题的成因、区域水资源条件,讨论农村饮水安全工程建设中水源的选择、工程形式确定、管理制度建设等方面的技术要点。     

浅谈给水工程水体消毒

对当前国内外给水工程中常用的源于漂白粉消毒技术的液氯、二氧化氯和氯胺消毒技术,以及臭氧和紫外线等主要消毒技术进行了比较,简要介绍了各种消毒方法的消毒机理、运行特性,分析、讨论各种消毒技术的特点、适用范围．氯系消毒技术成熟,可单独使用或组合使用;紫外线消毒和臭氧消毒技术由于消毒速度快、有效时间短,可作为联合消毒技术的重要组成部分来应用．另外,探讨了未来给水工程水体消毒技术的发展方向．为给水工程消毒技术方案选择、减小水体消毒有害副产物浓度提供参考．