Water status in winter wheat grown under salt stress

1 IntroductionSalinization is one of the major problems in arid and semi-arid regions in relation to land use and in particular to agricultural production[1]. Excessive salinity leads to toxicity in crops and reduction of the availability of water to crops, by reducing the osmotic potential of the soil solution[2]. Movement of soil water induces solute transport, and solutes are transferred towards the ground surface by the upward soil-water movement caused by evaporation, resulting in an accu…     

Water status in winter wheat grown under salt stress

Properties of the soil surface layer, the temporal pattern of the microclimate variables as well as crop condition were combined to analyze the characteristics of the evapotranspiration from winter wheat fields in a saline soil area. In order to accomplish this analysis, evapotranspiration was divided into evaporation from the soil and transpiration from wheat. Moreover, the effect of soil salinity on evapotranspiration was evaluated through the relationship between actual evapotranspiration and potential evapotranspiration (Ea/Eo) and the total soil water potential (y) was divided into two components: matric potential (yM) and osmotic potential (yo). Two sites with different salinity levels were chosen for this study, located in Hebei Province, China. Measurements were conducted in April-May 1997 and May 1998. The Bowen ratio method was used to estimate the actual evapotranspiration (Ea), whereas potential evapotranspiration (Eo) was estimated using Penman’s equation. Measurements of soil evaporation (Es) were obtained with micro-lysimeters, and transpiration was calculated from the difference between Ea and Es. The results show that transpiration comprised on average almost 80 % of total evapotranspiration. Evaporation from the soil differed slightly between years, but this variation was dominated by the leaf area index (LAI), which ranged from 4 to 5 during the study period of 1997 and 1998. Soil electric conductivity (EC), which is directly related to osmotic potential, ranged from 1.9 to 3.5 mS cm-1 in 1997 and was negligible in 1998. Our results indicate that lower osmotic potential decreases the total soil water potential, thus affecting plant transpiration. Hence, it is possible to say that soil salinity actually decreases evapotranspiration from winter wheat fields.     

莫高窟窟顶风况及输沙势研究

以1998—2001年莫高窟窟顶自动气象观测站记录的风资料为基础,通过对风况的统计和输沙势的计算,从风沙环境特征阐明了研究区主要受西北、东北和偏南三组风向共同作用。三组风况出现频率明显不同,其输沙势有一定差异。研究区风向变率指数较小,风况复杂,属于中风能环境。通过对风况的分析及输沙势的理论计算,以期对莫高窟的风沙危害防治提供科学理论依据。最后通过对莫高窟2001年输沙势（量）的对比计算,指出了现有输沙势公式存在的局限与不足。     

农村居民点土地整理潜力研究方法述评

结合我国农村居民点土地整理潜力研究现状,将农村居民点土地整理研究归纳为综合潜力评价与农村居民点土地整理潜力计算方法两项主要研究内容;评述政策指标测算法、闲置宅基地抽样调查法和建筑容积率法3种农村居民点土地整理潜力计算方法,并探讨农村居民点土地整理潜力理论缺乏系统性、综合潜力研究中土地整理适宜性评价与综合潜力评价重叠及农村居民点土地整理潜力计算方法尚不完善等问题;提出农村居民点土地整理潜力研究应与耕地整理等其他土地整理领域相结合,使农村居民点土地整理潜力计算方法更系统、更精确。     

中国滑雪场可达性及市场潜力测度

利用可达性分析方法与潜力模型对中国滑雪场空间分布格局与市场潜力进行了系统分析,全面认识了滑雪场在交通可达性方面的优劣势,并针对不同区域提出了相应的发展或改进方向.研究表明:中国滑雪场距离城市中心的平均最短旅行时间为1.24 h,南方可达性普遍较差,北方同一城市内部差异较大.全国各城市到达某一滑雪场的最短时间呈圈层式分布...     

中国荒漠化潜在发生范围的修订

为了客观反映中国荒漠化发生区域,按照联合国防治荒漠化《公约》的定义,利用1950-1990年间全国671个气象站的长时间序列气象数据,分别采用Thornthwaite和Penman计算可能蒸散量的方法计算了湿润指数的分布,然后根据中国气候区划和中国植被区划以及中国荒漠化发生的特点等对计算结果进行了调整,对中国荒漠化潜在发生范围进行了修订,明确了荒漠化各气候类型区的地理涵义。研究结果表明：①《公约》定义的荒漠化潜在发生范围及各气候类型区的划分标准不完全适用于中国。②中国的荒漠化发生在极干旱区、干旱区、半干旱区和亚湿润干旱区。极干旱区对应极旱荒漠,干旱区对应典型荒漠、草原化荒漠以及荒漠草原,半干旱区对应典型草原,亚湿润干旱区对应草甸草原中偏干旱的部分。③修订后中国荒漠化潜在发生范围总面积约4 524 089.1 km²,约占国土总面积的47.1％,其中亚湿润干旱区、半干旱区、干旱区和极干旱区分别占12.6％、28.8％、34.4％和24.2％。荒漠化潜在发生范围修订后比修订前增加1 207 056.9 km²,其中亚湿润干旱区面积减少,半干旱区、干旱区和极干旱区面积增加。     

云南省区域综合发展潜力评价与发展对策研究

选择云南省为实证区域,建构了主导影响因素-基于层次聚类的空间叠加法,评价云南省区域综合发展潜力.全省县域综合发展潜力空间上呈现滇中高、外围低,交通干线与城镇节点区域高、乡村区域低的特点;且滇中初步形成中心-外围格局,滇东南、滇西与滇南初步形成点状.区域发展潜力与交通条件和经济发展基础呈高度正相关,综合评价将云南省分为高、中、低3类潜力区域,其发展模式分别为:技术与体制创新的新型工业化道路和"有序化、高效益"的城市群发展模式;积极推动县域产业规模化、特色化、集约化集聚城镇密集区;以生态环境保护为主要目标的产业发展模式和城镇化模式.     

基于技术效率测算的京津冀城市土地集约利用潜力评价

现有城市土地集约利用潜力评价研究主要采用多指标综合评价方法,存在依据不充分、结果不可比、难反映动态变化等缺陷。针对此,基于集约潜力和技术效率的概念联系,把城市土地集约利用潜力定义为是城市土地利用技术效率的潜在提升所可能带来的土地节约量或产出增加量,构建了城市土地集约利用土地节约潜力和产出增长潜力定量评价模型,测算和分析了京津冀2006-2015年城市土地集约利用土地节约潜力和产出增长潜力的规模与占比情况。结果表明：① 京津冀城市土地集约利用潜力规模巨大且持续增加,土地节约潜力规模10年均值为709.80 km ²、净增量达543.96 km ²,产出增长潜力规模（2005年不变价）10年均值为4207.57亿元、净增量达3428.55亿元;② 京津冀城市土地集约利用潜力占比很高且持续提升,土地节约潜力占比10年均值为21.80%、净提高10.56个百分点,产出增长潜力占比10年均值为26.12%、净提高14.73个百分点;③ 京津冀13个城市土地集约利用潜力排名很稳定,且差距在扩大,显示出越发达城市集约挖潜越困难、越落后城市集约挖潜越容易的一般规律,以及集约挖潜容易者更加容易、困难者更加困难的马太效应。研究能够为城市土地集约利用实践与管理提供科学指导,有利于推进集约评价和效率测算研究之间的对话与交流。     

台湾居民休闲消费潜力综合测度及系统评估研究

通过构建指标体系以及测度和评估模型,并采集1998—2017年相关统计数据,对台湾居民休闲消费潜力进行综合测度和系统评估。研究发现：第一,休闲消费环境对台湾居民休闲消费潜力影响相对较大,其中文化与休闲活动参与尤为关键;第二,台湾居民休闲消费潜力总体保持梯度上升态势,潜力等级已跃升至中高水平;第三,台湾居民休闲消费支出指数和休闲消费环境指数显著提升,子系统指数等级在时间分布上存在明显差异;第四,耦合度分析认为,台湾居民休闲消费潜力子系统及要素之间存在较强的相互作用;协调度分析进一步发现,台湾居民休闲消费潜力始终处于协调阶段且协调等级稳步上升。     

Spherical harmonic representation of the gravitational potential of discrete spherical mass elements

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We present expressions in a spherical harmonic framework for the gravitational potential of discrete point, surface, and volume mass elements located at any depth within a sphere. Through analysis of the spherical harmonic spectrum, insight is gained into the properties of the potentials arising from a variety of mass distributions. A point mass at the surface of a sphere displays the richest harmonic spectrum in all degrees; spectra become increasingly reddened as the source mass is distributed through larger elements of area or volume, or is located at greater depths below the surface of the reference sphere. The spectra of dipolar distributions, useful in representing compensated masses, are depressed, especially in the low harmonic degrees, relative to the spectra of monopole elements.     

A general model for estimating actual evaporation from non-saturated surfaces

Based on energy balance equation and mass transfer equation, a general model to estimate actual evaporation from non-saturated surfaces was derived. Making use of two concepts, “relative evaporation” and “relative drying power”, a relationship was established to account for the departure from saturated conditions. Using this model, the actual evaporation (evapotranspiration) can be calculated without the need of potential evaporation estimation. Furthermore, the model requires only a few meteorological parameters that are readily and routinely obtainable at standard weather stations. Based on nearly 30 years data of 432 meteorological stations and 512 hydrological stations in China, in combined with GIS, nine typical river basins were selected. Using the data of the selected river basins, the model was tested. The results show that the actual evaporation rate can be estimated with an error of less than 10% in most areas of China, except few years in the Yellow River Basin.     

A general model for estimating actual evaporation from non-saturated surfaces

Based on energy balance equation and mass transfer equation, a general model to estimate actual evaporation from non-saturated surfaces was derived. Making use of two concepts, "relative evaporation" and "relative drying power", a relationship was established to account for the departure from saturated conditions. Using this model, the actual evaporation (evapotranspiration) can be calculated without the need of potential evaporation estimation. Furthermore, the model requires only a few meteorological parameters that are readily and routinely obtainable at standard weather stations. Based on nearly 30 years data of 432 meteorological stations and 512 hydrological stations in China, in combined with GIS, nine typical river basins were selected. Using the data of the selected river basins, the model was tested. The results show that the actual evaporation rate can be estimated with an error of less than 10% in most areas of China, except few years in the Yellow River Basin.     

黄土高原旱作区马铃薯叶片和土壤水势对垄沟微集雨的响应特征

于2011年在黄土高原半干旱地区以平地不覆膜为对照,研究了不同沟垄和覆膜方式对马铃薯叶片和土壤水势水势的影响。结果表明：不同沟垄和覆膜方式在不同土层和不同生育期对土壤和叶片水势的影响差异显著。（1）土壤水势日变化趋势：0～20 cm土层,土垄处理在开花期为先下降后上升型,土垄和覆膜垄处理在块茎膨大期为先下降后上升型,覆膜垄和全膜双垄沟播处理在成熟期为先下降后上升型,其余为逐渐下降型;20～40 cm土层,各处理土壤水势呈逐渐下降趋势。（2）叶片水势日变化趋势：开花期和块茎膨大期表现为双低谷型,双低谷分别在13：00和17：00,成熟期为“V”型,即单低谷型,低谷出现在17：00。各处理变化趋势相同,但水势存在差异。土垄处理在水分关键期（开花期和块茎膨大期）叶片水势显著高于其他处理,而全膜双垄沟播处理在成熟期最高。（3）生育期土壤水势和叶片水势均表现为先减小后增大的趋势。20～40 cm土层对叶片水势影响较大,土垄处理在该土层具有较好的水分状态,蒸腾作用较强加速了水分运移速率,是导致覆膜垄和全膜双垄沟播处理水势低于土垄的主要原因。在前期降雨较少的年份,由于较小的蒸腾作用,土垄处理可以保证马铃薯承受较小的水分胁迫;在前期降雨量较多的年份,覆膜垄和全膜双垄沟播处理则可以凭借其较大的蒸腾作用发挥较大的增产效果。     

区域持续发展的指标研究

本文在总结、概括已有指标的基础上,提出了区域人地相互作用潜力三维指标体系,通过这一潜力空间来综合测度区域持续发展水平,能力和前景。本文在总结,     

城镇建设用地集约利用潜力释放技术研究——以兰州市为例

在当前国家推行节约型社会、严格土地集约利用及管理的宏观环境下,城镇建设用地集约利用已经引起广泛关注。如何对存量城镇建设用地的集约利用潜力进行测算和挖掘,是城镇发展规划建设的重要问题。在土地集约利用评价的基础上进行了潜力测算,并进一步考虑潜力的空间释放方案。研究结合智能模拟方法,通过调整模型参数,对多套方案进行了演化模拟,最后从形态紧凑的角度进行了方案评价与优选。结果显示,该方法体系可操作性强,研究结果在数量和空间方面可视化程度高,模拟方案可作为规划参考。     

潜在生态风险指数法应用中的一些问题

收集2001—2018年有关Håkanson潜在生态风险指数法应用论文2323篇,重点分析2008年以来发表在国内外著名期刊上的论文203篇,发现存在以下问题：① Håkanson潜在生态风险指数是基于水环境沉积学理论建立的一种生态风险评价方法,不适合土壤潜在生态风险或污染评价,更不能被应用于水相溶质、大气颗粒物、地表灰尘、植物或作物等介质的生态风险或污染评价,但现实研究中评价对象错位的论文占2323篇论文的49.29%。② 不能生搬硬套Håkanson潜在生态风险系数（Er）和潜在生态风险指数（RI）分级标准,必须根据具体参评污染物的种类和数量进行调整。Er第一级界限值应为所有参评污染物毒性系数（St）的最大值,RI第一级界限值可用∑St ⁱ×1.13并取十位整数得到。但是多数研究罔顾其参评污染物的种类和数量,照搬Håkanson的Er和RI分级标准而出现错误的论文分别占203篇论文的45.32%和61.08%;虽然有些学者对RI分级标准进行了调整,但调整正确的论文只占23.81%。③ 只评价Hg单项生态风险或包括Hg在内的多个重金属综合生态风险时,不能用St ^Hg代替其毒性响应系数（Tr ^Hg）。     

Growth and water relation parameters in drought-stressed Coriaria nepalensis seedlings

In the present study, growth and water relation parameters were analysed in drought-stressed Coriaria nepalensis Wall. seedlings. C. nepalensis seedlings were subjected to four drought cycles of 7, 14, 21, and 28-days, and to one control level (watered on alternate days) in a glasshouse. The seedlings failed to survive a 28-days drought during summer. Osmotic adjustment (defined as the decrease in osmotic potential at zero or full turgor in response to water deficit) was measured as the difference between the osmotic potential of seedlings watered on alternate days (control) and those subjected to 21-days drought cycle. Seedlings subjected to 21-days drought had a predawn water potential of −2.60 MPa, and showed an osmotic adjustment of −1.95 MPa at full turgor and −2.17 MPa at zero turgor. The growth of seedlings was positively related to moisture and with water potential. With decline in soil moisture the root:shoot ratio increased while leaf weight ratio decreased. Leaf characteristics, such as leaf number, leaf area, leaf area ratio, specific leaf area and leaf drop, were also affected by moisture stress. This study has indicated that osmotic adjustment is a major adaptive mechanism of C. nepalensis that aids successful regeneration of seedlings in degraded sites with inhospitable soil conditions.     

位涡分析在新疆暴雨研究中的初步应用

新疆是全国有名的干旱、半干旱地区,年平均降水量约147mm,不到全国平均值的1/4,但暴雨造成的洪水却是新疆的主要灾害之一。随着新疆气候由“暖干”向“暖湿”型的转变,暴雨出现的频率可能会增加,暴雨带来的洪涝也有可能比以往更加严重,因此有必要加强对新疆暴雨天气的分析研究。本文根据位涡理论,选取2004年7月18日～20日的一次由中亚低涡造成的盛夏暴雨过程做个例分析,对位涡与新疆地区降水和暴雨的关系进行了初步研究。结果表明：对流层高层十位涡能较好地反映冷暖空气的活动及天气系统的演变特征,位涡场比温度场、高度场能更清楚地示踪冷空气,这为研究冷空气的活动,特别是冷空气在触发暴雨中的作用提供了新的思路;对流层低层湿位涡与降水的强弱有良好的对应关系,当包线陡立时,易导致倾斜涡度发展,出现降水：当湿位涡MPV〈0时,在θe线陡峭密集区内易出现暴雨。