中国风水侵蚀交错区分布特征分析

风水侵蚀交错带的研究 ,对景观、土地覆盖 /土地利用、全球变化等研究具有重要意义。论文以GIS技术为支撑 ,定量计算出我国风水侵蚀带。在分布特征上 ,主要分布我国北方地区 ,其中以西部沙漠 ,北部山脉沿线为重 ,这种分布与气候、地貌分界有明显联系。 49.6 %风水侵蚀复合带的降水量小于 2 0 0mm。风水侵蚀复合带的土地利用主要以草地为主 ,占 41.8% ,其次为耕地。两种类型的分布 ,草地以与其它土地利用类型交错分布为主 ;而耕地是有重心的分散分布。风水侵蚀复合带的总体侵蚀要强于全国水平。     

Alternative Route of Infection for Bacterial Seedling Blight of Rice Caused by Burkholderia plantarii

Burkholderia plantarii , the pathogen of bacterial seedling blight of rice, was detected in paddy water. Its concentration rose in July and August. The bacterial concentration in the paddy water was always higher along levees than at distances more than 5 m from levees. Confirmed to be released into water when graminaceous weeds were immersed, B. plantarii survived for at least 4 days at 30°C. B. plantarii was splashed at least 30 cm upward by rain splash in the field. Harvested seeds, which had been sprayed with B. plantarii released from graminaceous weeds at the flowering stage, retained the bacteria. Bacterial seedling blight occurred when the seeds were then sown in nursery boxes. These results indicated that graminaceous weeds growing on levees of paddy fields are a source of infection of the disease and that rice seeds are infected through the paddy water. Received 23 May 2002/ Accepted in revised form 1 September 2002     

Observations of Phytophthora spp. in Water Recirculation Systems in Commercial Hardy Ornamental Nursery Stock

Samples of water and sediment were taken from drains, reservoirs and wells from four commercial hardy ornamental nurseries with water recirculation systems. The samples were taken on seven different dates throughout a single year from August 1994 to July 1995. The samples were screened for Phytophthora species using five different methods: direct plating, three bait tests (using lupin seedlings, apples and Rhododendron leaves) and a DAS-ELISA (double-antibody sandwich enzyme-linked immunosorbent-assay) with two antisera. In the nurseries with old water recirculation systems, Phytophthora species were detected in the drains and in the reservoirs. In the nursery with a new recirculation system, the pathogens were only present in the drains. None of the water samples from wells in any of the nurseries were contaminated. Phytophthora species were present in the water as well as in the sediment samples from drains and reservoirs. They were detected in the water recirculation systems irrespective of the season. The number of isolates increased about sevenfold between late summer and spring. At least 12 different Phytophthora species were identified: some isolates were previously unrecorded species. The epidemiology of the pathogens in outdoor water recirculation systems as well as the importance of the results for commercial nurseries is discussed.     

Variation in the development of secondary dormancy in oilseed rape genotypes under conditions of stress

Summary A substantial amount of seed is left in the fields before and during harvest of oilseed rape. Although this crop exhibits little or no primary dormancy, the absence of certain environmental cues that promote germination of imbibed seeds induces secondary dormancy. The work reported investigated the extent to which environmental stress conditions, including osmotic stress, low oxygen stress and anaerobiosis, induce secondary dormancy in oilseed rape, and examined the variation in development of secondary dormancy between and within genotypes. Osmotic stress was most effective in inducing dormancy. Anaerobic treatment produced very few dormant seeds, as did an atmosphere low in oxygen and high in nitrogen. The development of secondary dormancy under osmotic stress varied considerably between and within genotypes. Dormancy ranged from almost zero to about 60% for winter genotypes and about 85% for spring types. Within genotypes, variations occurred between seed lots and years of harvest. Temperature variations affected the percentage of dormant seeds. More dormant seeds were likely to be produced with incubation under water stress at 20 °C than at 12 °C. In winter genotypes, fewer dormant seeds were produced when incubation temperature and germination test temperatures differed. Thus, incubating at 20 °C and 12 °C, followed by germination tests at 20 °C and 12 °C, respectively, produced most dormant seeds. Also, in the winter genotypes, the potential development of secondary dormancy was positively correlated with the pattern and speed of germination of untreated seeds.     

黑河干流中游地区耗水量变化的历史分析

黑河流域水资源极其匮乏 ,加之地区上的配置不均衡和中游地区水土资源的过度开发导致了黑河下游严重生态环境问题 ,已影响到我国北方广大地区生态环境质量 ,受到国家的高度重视和全社会的广泛关注。黑河水资源开发利用主要集中在中游地区 ,该区是全国重要的商品粮、蔬菜和经济作物生产基地之一 ,耗水量占流域耗水量的 85 %以上 ,是黑河的主要耗水区和径流利用区。本文利用黑河上游控制站莺落峡站和中游控制站正义峡站水文资料 ,分析了黑河中游耗水量的变化 ,结果表明 :2 0世纪 80年代以前黑河中游耗水量在 4.2 0× 10 8m3 左右 ,比较稳定 ;进入 2 0世纪 80年代以来耗水量明显增加 ,80年代耗水量比 40年代末期至 70年代增加了 2 .0× 10 8～ 2 .5×10 8m3 左右 ;90年代耗水量又比 80年代增加了 1.6 0× 10 8m3 左右。 80年代以来流域耗水量呈明显增加的趋势 ,这是以人类活动影响为主的结果     

黑河流域荒漠地区梭梭人工林地土壤水分动态研究

梭梭林地土壤剖面的含水量与裸沙地含水量显著不同 ,裸沙地土壤含水量随深度增加而增加 ,林地在 30～ 12 0cm范围内有较高的含水量 ;林地 0～ 30cm的上层土壤含水量受降雨及蒸发的剧烈影响 ,30～ 2 0 0cm范围内的林地土壤各测量层平均含水量与其标准差有二次函数的关系 ;降雨对每月的 0～ 2 0 0cm的土壤贮水量没有明显的影响 ,说明降雨多数在当月就被蒸散和深层渗漏所消耗 ;认为梭梭人工林这种脆弱生态系统能够在严酷的环境条件下存在 ,其根系对土壤水和地下水有吸水和释水的再分配功能是重要的因素之一     

孔雀河流域绿洲生态支持系统调控模式研究

生态环境用水量的减少是孔雀河流域近 50年来现代绿洲环境退化的主要原因 ,维持生态与社会经济的合理用水比例是绿洲系统持续发展的前提。以此为基础 ,本文采用水资源承载力的方法探讨了绿洲生态支持子系统和社会经济子系统优化调控模式 ,最后就配置方案及发展模式的可行性进行了分析     

民勤绿洲生态气候资源及其利用

民勤绿洲边缘 ,光照丰富、温差大 ,有利于农产品质量的提高。但是水资源缺乏 ,地下水位急剧下降和土地沙化是民勤绿洲农业生产的首要问题。如何充分利用现有生态资源 ,并充分提高其利用率是摆在我们面前的一个主要课题。只有通过引进优良品种 ,调整农业种植结构 ,大力推广节水灌溉技术 ,才是解决上述问题的有效途径     

Effect of air temperature, rain and drought on hot water weed control

The influence of rain and drought before, and air temperature during, weed control with hot water was studied in laboratory experiments on the test weed Sinapis alba (white mustard). The plants were grown in a greenhouse and treated outdoors. There was no difference in weed control effect when S. alba plants at the four‐leaf stage were treated at the air temperatures 7°C and 18^°C. The effective energy dose for a 90% fresh weight reduction was 465 kJ m^?2 for both air temperatures. Weed control of S. alba at the four‐ to six‐leaf stage in rainfall above the rainwater run‐off level increased the required effective energy dose by 20% (i.e. 120 kJ m^?2) compared with dry plants. A short period of drought just before treatment on S. alba at the two‐ to four‐leaf stage increased the plant fresh weight reduction, which was 22% at low energy dose (190 kJ m^?2) and 44% at high energy dose (360 kJ m^?2). Hot water weed control should thus be carried out when the plants are drought stressed and avoided when the plants are wet. The air temperature seems to be of little importance in the range 7–18^°C.