Competition and interactions among stripe rust pathotypes in wheat-cultivar mixtures

A series of experiments was conducted with wheat stripe rust to analyse competition between simple and complex pathotypes in host mixtures. Two different pathotype combinations were tested, with different host components. Each combination included a complex (able to infect two host components) and two simple pathotypes. For one of the combinations, induced resistance was tested in a separate experiment as a possible interaction among pathotypes. Disease severity and pathotype frequencies were measured three times during the epidemic, on each host component grown in pure stands and in mixtures. In one of the experiments, pathotype frequencies were also measured within secondary foci. One of the complex pathotypes appeared to have a low fitness on one of the host components and did not significantly increase in frequency in host mixtures relative to pure stands. The average frequency of the other complex pathotype increased during the first epidemic cycles, but remained stable afterwards, below expected values. The results suggest that the development of complex pathotypes in host mixtures may be influenced by differential aggressiveness on the host components, by induced resistance and by random effects resulting from the formation of disease foci, and depends on pathogen autoinfection rate and dispersal mechanisms.     

华东地区部分猪源大肠杆菌K88黏附素的生物学特性

近年来，从华东地区患腹泻仔猪中分离到一些表达K88菌毛的大肠杆菌，这些菌株只与K88a因子单抗反应，而不与b、c、d因子单抗反应。通过K88常规血清交叉吸收试验、SDS-PAGE、Western印迹，表明这些菌株不仅与K88ac参考菌株C83907制备的c因子血清反应，而且与以分离株SEC586制备且经K88ab、K88ac、K88ad参考菌株吸收后的血清也反应。对分离株SEC586、SEC464的K88主要亚单位结构基因faeG的克隆、测序，发现该基因由846对核苷酸组成，编码菌毛主要亚单位的262个氨基酸及21个氨基酸的信号肽，比国外报道的K88ac FaeG亚单位（263个氨基酸）少了1个氨基酸，比K88ab、K88ad（265个氨基酸）少了3个氨基酸。SEC586、SEC464菌株的FaeG亚单位氨基酸序列的同源性为97．7％，它们与K88ac的同源性为94．7％和96．2％；与K88ab的同源性为90．1％和91．2％；与K88ad的同源性为87．0％和88，6％。结果表明，新分离的K88ac大肠杆菌黏附素主要亚单位已发生了部分变异。     

中药复方总多糖及其含药血清对小白鼠免疫功能的影响

分别给小鼠灌服复方总多糖、复方水煎剂、黄芪多糖、生理盐水后制备含药血清,用MTT法测定小鼠淋巴细胞增殖程度,用酶法一氧化氮试剂盒测定腹腔巨噬细胞一氧化氮的生成量,同时与各种药物的体外实验相比较.结果显示,复方总多糖及其含药血清均能促进小鼠脾脏淋巴细胞增殖和腹腔巨噬细胞一氧化氮的生成量,且效果优于复方水煎剂和黄芪多糖.     

集雨栽培冬小麦田土壤水分和矿质氮

在半湿润易旱地区的关中红油土上,研究了垄上覆膜集雨栽培措施对冬小麦(Triticumaestivum)田土壤水分和矿质氮的影响。结果表明覆膜有一定的蓄水保墒效果,冬小麦返青期,0～40cm土壤贮水量覆膜处理比不覆膜处理平均多7.7mm;覆膜能使冬小麦在生长后期更有效地利用土壤深层贮水,在小麦成熟期,100～200cm土壤贮水量覆膜处理比未覆膜处理少23.8mm。覆膜有利于作物对氮肥的吸收利用,氮肥用量相同的处理,覆膜条件下的硝态氮浓度和矿质氮累积量低于不覆膜处理;施氮也可以明显增加土壤剖面中的硝态氮含量和矿质氮累积量。     

旱地莜麦多目标动态施肥模式研究

建立莜麦籽粒产量、生物产量、籽粒蛋白质产量、总蛋白质产量与施氮总量及追施比例之间的效应方程,求解不同边际利润下的最佳施氮量及追施比例。结果表明施氮量改变,直接影响最佳追施比例、籽粒产量、蛋白质产量和生物产量等,施氮量在17.25～120.75kg/hm2区间内,各种目标产量随施氮量的增加而稳定增加,在合理的施氮量区间内实现既定产量,施氮总量与追施比例可以消长互替,降低追施比例则增加氮素总量,或增加追施比例则可以减少氮素总量。得出了不同目标产量时的最佳氮肥用量与追施比例和对应于氮肥不同用量的最佳追施比例及理论产量的动态施肥模式的数学方程。     

0～50 cm与0～100 cm土层土壤湿度的转换关系研究

对郑州、南阳2个测点多年来0～100cm土壤湿度、降水(灌溉)及作物发育期资料进行了分析。结果表明,按土壤湿度随时间的变化规律,可将其划分为秋季缓慢下降期、冬季相对稳定期、春季迅速下降期和夏季增墒期4个时段。对0～50cm与0～100cm土层土壤湿度进行回归分析,当前期降水量在10mm以下时,用直线或二次曲线拟合效果良好;当前期降水(灌溉)量大于10mm时,0～50cm与0～100cm土壤湿度之比与前期降水(灌溉)量呈双曲线或二次曲线关系,拟合曲线考虑降水(灌溉)时回归效果有所提高。同一土壤类型、不同时段,或同一时段、不同的土壤类型,拟合的方程不同,反映出不同层次土壤湿度关系的复杂性。     

乌兰布和沙漠流动沙丘不同部位水分动态研究

通过对乌兰布和沙漠流动沙丘的不同部位沙土含水量的测定研究，结果表明：（1）乌兰布和沙漠流动沙丘3个不同部位的水分垂直变化趋势是一致的，0～60cm含水量变化幅度大，60～100cm变化幅度小，含水量最大值出现在20～60CITI，降雨主要影响60cm以上的沙土水分；（2）3种部位在时间变化上都表现为4～5月含水量最小，从6月开始含水量升高；（3）迎风坡含水量较其他部位大0．65％～0．9％，较背风坡大1．8％～2．5％，其他部位较背风坡大1％～1．7％，且3种地貌部位20～60cm处较80cm和100cm处有较大差异，同时迎风坡的变化幅度最大。     

Placing the pieces: Reconstructing the original property mosaic in a warrant and patent watershed

Recent research shows that land use history is an important determinant of current ecosystem function. In the United States, characterization of land use change following European settlement requires reconstruction of the original property mosaic. However, this task is difficult in unsystematically surveyed areas east of the Appalachian Mountains. The Gwynns Falls watershed (Baltimore, MD) was originally surveyed in the 1600-1700s under a system of warrants and patents (commonly known as ‘metes and bounds’). A method for the reconstruction and mapping of warrant and patent properties is presented and used to map the original property mosaic in the Gwynns Falls watershed. Using the mapped mosaic, the persistence of properties and property lines in the current Gwynns Falls landscape is considered. The results of this research indicate that as in agricultural areas, the original property lines in the Gwynns Falls watershed are persistent. At the same time, the results suggest that the property mosaic in heavily urbanized/suburbanized areas is generally ‘reset.’ Further, trends in surveying technique, parcel size, and settlement patterns cause property line density and property shape complexity to increase in the less urbanized upper watershed. The persistence of original patterns may be damping expression of heterogeneity gradients in this urban landscape. This spatial pattern of complexity in the original mosaic is directly opposite of hypothesized patterns of landscape heterogeneity arising from urbanization. The technique reported here and the resulting observations are important for landscape pattern studies in areas settled under unsystematic survey systems, especially the heavily urbanized areas of the eastern United States. This revised version was published online in July 2006 with corrections to the Cover Date.     

戊唑醇在苹果和土壤中的残留分析方法

本文建立了戊唑醇在苹果和土壤中残留的液相色谱分析方法.该方法仪器最低检出量为4×10-11g;最低检出浓度为0.002mg/kg;平均回收率为85.6%～102.2%;变异系数为2.85%～9.47%。     

黄土地区影响土壤膨胀因素的研究

通过测定黄土高原地区几种土壤的膨胀率,探讨了不同质地、有机质、容重、Ca2 、干湿交替强度和次数对土壤膨胀率的影响,揭示了这些因素对土壤结构的影响程度。结果表明:土壤粘粒含量与土壤膨胀率呈显著正相关;有机质含量在质地差别不明显情况下,对土壤膨胀率也有极显著的作用与影响;容重对土壤膨胀率的影响是随着容重的增加土壤膨胀率也增加,增幅可达1.70%~30.22%;Ca2 对土壤膨胀起着重要的抑制作用。干湿交替强度显著地影响着土壤膨胀性,在40℃情况下快速干燥土壤的膨胀率较在30℃时干燥的土壤膨胀率显著增幅可达30.28%~81.20%;干湿交替次数对土壤膨胀率的作用表现为随着干湿交替次数的增加而增大,尤其以第一次干湿交替的破坏最为严重。