磷指数模型在美国的应用和发展

磷是植物生长必需的营养元素之一,在农业生产中起着关键作用。然而,长期过量的磷肥投入导致土壤磷素水平增加,进而加大了土壤磷素流失风险,造成农业非点源磷污染,同时这也成为导致水体富营养化的主要因素之一。因此,识别和管理农业非点源磷的流失风险关键区,成为面源污染亟待解决的关键问题。磷指数模型起源于20世纪90年代,是评估农田磷流失潜力和指导磷管理决策的重要工具之一。根据研究区特点,美国众多学者在各州设立了不同的磷指数指标体系,优化了磷指数的组成因子、计算方法和分级标准。本文对美国各州磷指数模型评价体系进行了综述和评价,指出了磷指数模型的局限性,提出了改进方向,以期为我国磷素管理方法提供借鉴。     

叶面喷施锌肥对小麦产量和效益的影响

以烟农19为试材,以喷施清水为对照,进行了锌肥不同时期和用量对小麦产量和效益的影响。结果表明：小麦施锌后产量提高,其中以苗期和拔节期各喷1次效果最好。     

2014年浑善达克沙地黄柳生长季水分来源同位素示踪研究

黄柳是我国内蒙古东部和辽宁西部沙丘上广泛分布的多年生灌木,是极佳的固沙树种.通过利用氢同位素示踪方法,测定了2014年浑善达克沙地黄柳生长季茎干水与潜在水源(降水、土壤水、地下水)氢同位素比率δD值,并利用多源线性混合模型IsoSource,计算了黄柳对各潜在水源的利用比例.结果表明:在5月黄柳80％以上利用120 ～ 160 cm土壤水和地下水;6月主要吸收0～40 cm土壤水;7月主要吸收120～160 cm土壤水;8月以地下水为主要水源,利用率为82％.这表明生长在不同季节的黄柳对于各潜在水源的利用有特定的适应结果,同时也说明荒漠灌木可以通过自身的调节朝着最优的方向发展,实现最大限度的水分利用.     

Periodicity and gradients in dispersal ofAlternaria linicola in linseed crops

Conidia ofAlternaria linicola produced on infected linseed crops were mainly dispersed by wind. The numbers of conidia in the air above linseed crops collected by a Burkard spore sampler were greatest between 1200 h and 1300 h, when the relative humidity was lowest. Although numbers of conidia collected decreased with increasing height within and above the crop canopy, air-borneA. linicola conidia were present up to 80 cm above the crop canopy. Conidia ofA. linicola were transported by wind up to at least 40 m downwind from an artificial line inoculum source, but their numbers decreased with increasing distance from the source. In 1991, 1992, and 1993, the dispersal ofA. linicola conidia above linseed crops followed a seasonal periodicity which was influenced by weather conditions and cultural practices. The greatest numbers of conidia were collected during July, August and early September and coincided with periods favourable for sporulation and with an increase in the incidence of the disease in the senescent crop. Air-borneA. linicola conidia produced on point or line inoculum sources (naturally infected linseed stem debris) were responsible for the spread of the disease in linseed crops. In 1992 and 1993, the disease was first detected downwind from the sources, but by the end of the growing seasons, it had spread in all directions and up to 20 m and 60 m from the sources, respectively. Disease gradients were initially steep near the inoculum sources but they became flatter with time due to the secondary spread of the disease.     

A preliminary study of water use strategy of desert plants in Dunhuang,China

Water is a restrictive factor for plant growth and ecosystem stability in arid and semiarid areas. The dynamics of water availability in soils and water use by plants are consequently critical to ecosystem functions, e.g. maintaining a high resistance to the changing climate. Plant water use strategies, including water-use efficiency(WUE) and the main water source that a plant species utilizes, play an important role in the evaluation of stability and sustainability of a plantation. The water use strategies of desert plants(Tamarix chinensis, Alhagi sparsifolia, Elaeagnus angustifolia, Sophora alopecuroides, Bassia dasyphylla and Nitraria sphaerocarpa) in three different habitats(saline land, sandy land and Gobi) in Dunhuang(located in the typical arid area of northwestern China) were studied. The stable isotope of oxygen was used to determine the main water source and leaf carbon isotope discrimination was used to estimate the long-term WUE of plant species in the summer of 2010. The results suggest that: 1) the studied desert plants took up soil water below the depth of 80 cm; 2) T. chinensis in the three habitats used deeper soil water and T. chinensis in the Gobi site had higher WUE than those in the saline land and the sandy land. The results indicated that desert plants in Dunhuang depended on stable water source and maintained high WUE to survive in water limited environments.     

Visual MODFLOW在李官堡水源地水流模拟中的应用

数值模拟方法目前是模拟地下水流动和评价地下水资源量的主要技术方法之一。Visual MODFLOW软件具有系统化和可视化的突出特点,因此应用该软件建立地下水系统的数学模型,对沈阳市李官堡水源地的水流情况进行了模拟和预测。模拟结果表明,该水源地为建设项目提供所需的9.8×104m3/d水量是可行的。模型的建立对傍河型水源地的建设和开采水量的预测有一定的借鉴价值。     

锌对黄瓜幼苗根系生长及保护酶活性的影响

为促进科学合理施用微量元素肥料、培育黄瓜壮苗,进一步提高黄瓜产量和品质,以‘新津春4号’黄瓜为材料,缺锌的1/2 Hoagland营养液为基础,设置4个不同浓度的ZnSO4?7H2O处理(0、0.1、0.2、0.4 mg/L)。通过营养液水培的方法,研究不同锌浓度对黄瓜幼苗根系生长及保护酶活性的影响。结果表明：（1）随着锌浓度的增加,黄瓜幼苗根系的总长度、平均直径、总面积、总体积、根尖数逐渐提高,Zn3(0.4 mg/L)时达到最大。（2）在Zn0(0 mg/L)到Zn2(0.2 mg/L)范围内,随着锌浓度的提高,POD、CAT活性升高,当锌浓度大于Zn2时,POD、CAT活性降低;SOD活性随着锌浓度的增加显著提高;丙二醛(MDA)含量随着锌浓度的增加显著降低。（3）综合考虑的黄瓜生长生理指标,黄瓜幼苗根系生长的最佳ZnSO4?7H2O浓度为0.2 mg/L的1/2 Hoagland营养液。     

电力系统脆性源辨识初探

电力系统的脆性源是电力系统脆性激发的源头,基于直流潮流和分布因子法相结合,提出了快速找到系统脆性源的方法和步骤,并以三母线电力系统脆性源辨识为例,证明了此方法的有效性。     

百色干热河谷地区降雨氢氧稳定同位素特征及芒果树水分来源研究

百色市右江河谷是我国著名的干热河谷之一,干旱是该地区最严重的气象灾害。芒果是该地区地理标志农产品,但其水分利用策略尚不清楚。本文基于氢氧稳定同位素示踪技术研究该地区降雨同位素特征及影响因素,利用多元线性混合模型方法量化不同来源水分对芒果树根系吸水的贡献比例,揭示芒果树生育期内水分利用策略。结果表明：（1）研究区氢氧稳定同位素具有明显的季节变化,δ值和氘盈余（d）具有旱季富集、雨季贫化的规律,建立了研究区的大气降水线方程：δD=8.2587δ18O+12.308,δD和δ18O值有极显著相关性（r=0.9968, n=35, P<0.001）;(2)季风气候影响下大气降水稳定同位素值具有显著的降雨量效应和反温度效应（P<0.05）;(3)在芒果花期、幼果期、果实膨大期和成熟期,土壤水氢氧稳定同位素总体上随土壤深度的增加而变贫;在花期和幼果期,芒果树对各层次土壤水分及地下水利用比例较为均匀,果树膨大期和成熟期则主要利用深层次土壤水及地下水,表明该地区芒果树主要以深层次土壤水及地下水为水源,说明芒果树更接近于保守型水分利用策略。降雨氢氧稳定同位素特征反映了该地区干热的气候特征,芒...