苦皮藤素类似物的合成与结构鉴定

以苦皮藤Celastrus angulatus Max.提取物水解产物中的多羟基β-二氢沉香呋喃为原料,合成了对粘虫Mythimna separata具有毒杀活性的苦皮藤素(Celangulin)类似物,并在活性追踪的指导下分离得到了两个具有杀虫活性的苦皮藤素类似物 A和B, 其结构经核磁共振谱、快原子轰击质谱、高分辨质谱等波谱学方法鉴定为2β,6α,8β,13-四异丁酰氧基-1β,4α,9α-三羟基-β-二氢沉香呋喃及1β,2β,6α,8β,13-五异丁酰氧基-4α,9α-二羟基-β-二氢沉香呋喃。化合物 A和B 均为新化合物,在20 mg/mL的浓度下对三龄粘虫Mythimna separata的胃毒活性(死亡率)分别为89.5%和93.2%。     

Effects of area and isolation of woodland patches on herbaceous plant species richness across Great Britain

Richness of Ancient Woodland Indicator plant species was analysed in 308 woodland patches that were surveyed during the Countryside Survey of Great Britain carried out in 1998. The Countryside Survey recorded vegetation plots and landscape structure in 569 stratified 1 km sample squares and developed a remotely-sensed land cover map of the UK. Using these datasets, we tested the hypothesis that Ancient Woodland Indicator species richness in woodland fragments was limited by patch area, shape and spatial isolation and that woodland patches located in the lowland region of Great Britain would respond differently than those in the upland region. The variation in Ancient Woodland Indicator species richness in the British lowlands (n = 218) was mainly explained by patch area and two measures of connectivity, the length of hedgerows and lines of trees in the 1 km square and the area of woodland within 500 m of the vegetation plot. By contrast, variation in Ancient Woodland Indicator species richness in the British uplands (n = 90) was related to Ellenberg scores of the vegetation communities sampled – a surrogate for habitat quality – and no significant effect of spatial structure was detected. It therefore appears that the degree of fragmentation of woodland in the British lowlands limits the distribution of Ancient Woodland Indicator species, while in the uplands, failed colonisation is a matter of habitat quality rather than a result of landscape structure.This revised version was published online in May 2005 with corrections to the Cover Date.     

鸭疫里氏杆菌形态特征的电镜观察

自鸭传染性浆膜炎的病死鸭中分离鉴定的鸭疫里氏杆菌(RA)Ⅰ、Ⅱ型两个菌株，用负染法和超薄切片法制备样品，于透射电镜下进行观察。结果观察到约占1／3的RA具有特殊的形态结构：在细菌的顶端或侧面有1～2个与菌体相连的芽状赘生物，有的也能从菌体上脱落下来。它在超薄切片中的大小约为菌体的1／3～1／5，能观察到其内部也具有类似菌体内部的结构。且具有类似菌体的“细胞壁”，类似于核体部分的结构位于“细胞壁”的一侧。而用相同的方法制作的鸭大肠杆菌(E．cozi)对照样品，却见不到这种特殊的形态结构。说明这种形态特征可能是RA特有的。     

Seed production of Chenopodium album in competition with field vegetables

Total weed control within a crop is both difficult and expensive to achieve, so that some weeds will often remain to set seed. The seed production resulting from these weeds will ultimately affect the sustainability of the weed control strategy. If too much is allowed to return each season there could be a gradual, but significant, increase in the potential weed flora over a number of seasons. Field trials were carried out in 2000 and 2001 to quantify the potential magnitude of this weed seed return from Chenopodium album L., grown at two planting densities either in pure stands or in competition with one of two crops (cabbage or onion). Crop and weed weights and weed seed production were notably greater in 2001. Both dry weight and seed production of C. album were suppressed by increasing planting density or by the presence of crop, with cabbage having a more suppressive effect. Despite the plasticity in seed production, a linear relationship was demonstrated between log weed seed production and log weed biomass that was robust over a range of competitive situations with onion and cabbage, at different planting densities and in growing seasons. The study also demonstrated that the relationship could be combined with an existing simple competition model to allow the consequences of incomplete weed control to be assessed in terms of potential weed seed return.     

Chromosomal and Plasmid Diversity of Agrobacterium Strains Isolated from Ficus benjamina Tumors

Agrobacteria were previously isolated from tumors developing on branches and aerial and hypogeous roots of weeping fig plants in Italy and in The Netherlands. A representative group of 48 strains was analyzed by PCR–RFLP of 16S and 16S + IGS ribosomal regions, PCR–RFLP of six Ti plasmid (pTi) regions and characterized for plasmid content. Two groups of agrobacteria were separated by cluster analysis of PCR–RFLP profiles of rrs gene: seventeen strains were similar to the new species Agrobacterium larrymoorei, while the remaining strains were included within the agrobacterium biovar 1 group. Sixteen different plasmid profiles from one to five plasmids were observed. In addition, 21 ribotypes and 20 pTi structures were arranged in many different combinations, showing that fig agrobacteria were characterized by a wide heterogeneity. A general lack of correlation between strain ribotypes and plasmid content was observed.     

鹰嘴紫云英头茬草生产性能的研究

通过对杨凌地区生长的鹰嘴紫云英（Astragalus cicer L.）的株高、株长、产量、草层结构、鲜干比、茎叶比等的研究表明：生长第二年第一茬初花期时刈割的鹰嘴紫云英平均株高达57 cm,株长达102 cm,鲜草产量达47 077.6 kg/hm^2,干草产量8 702.0 kg/hm^2,其茎、叶主要分布在0～40cm的草层中,茎、叶鲜重分别占到总重量的52.39%和31.88%,鲜干比为5.41：1,茎叶比为1.47：1,属典型的下繁型牧草,具产草量高、营养丰富、牧草品质好等优点,是值得推广的优良牧草.     

在放牧干扰下冷蒿种群脯氨酸含量的变化

对放牧干扰下土壤含水量、冷蒿体内含水量、脯氨酸含量变化进行的研究结果表明随着放牧强度的增加土壤含水量降低,冷蒿叶片、根中含水量呈下降趋势。在生长初期,随着放牧强度的增加冷蒿叶片内脯氨酸含量迅速积累;生长盛期脯氨酸含量虽随牧压有所增加,但增加的幅度较小;生长末期脯氨酸含量较高,而且随着牧压的增加略有下降。地下部分,脯氨酸含量在牧压梯度间变化较小。相关分析表明,在生长初期和盛期,冷蒿叶片、根的含水量与土壤含水量呈正相关,生长末期不相关。冷蒿脯氨酸含量与植物的含水量呈负相关,在生长初期和末期呈显著负相关,而生长盛期相关不显著;与此不同,在生长初期冷蒿体内脯氨酸含量与土壤含水量呈负相关,在生长末期二者负相关性不显著,这说明随着放牧干扰强度的增加土壤含水量降低,导致冷蒿体内水分胁迫增加,致使脯氨酸开始逐渐积累。而生长末期的降温和群落中植物种间竞争减少,使脯氨酸的积累速度也相应放慢。在放牧干扰下,脯氨酸大量积累,对冷蒿的生存和生长起到了重要的作用,是冷蒿种群耐啃食、耐践踏、逐渐取代禾本科植物而成为退化草原的优势植物的生理基础之一。     

纳豆菌、甘露寡糖对仔猪肠道pH、微生物区系及肠黏膜形态的影响

选取144头18日龄断奶，体重5．6kg的杜大长三元杂仔猪，按体重和性别分成6个处理，每组3个重复，每重复8头仔猪，研究纳豆菌（Natto）和甘露寡糖（MOS）对早期断奶仔猪肠道pH、微生物区系和小肠黏膜形态的影响。结果为：（1）Natto、MOS均有降低仔猪肠道pH的趋势（P＞0．05），Natto与MOS联用时显著降低仔猪空肠、回肠、盲肠和结肠内容物的pH（P＜0．05）；（2）Natto提高了仔猪结肠内容物中乳酸杆菌和双歧杆菌数量（P＜0．05），提高结肠黏膜中乳酸杆菌数量（P＜0．05），MOS提高了仔猪结肠内容物和黏膜中乳酸杆菌数量（P＜0．05），2g／kg的MOS组使结肠内容物和黏膜中大肠杆菌数下降（P＜0．05）。Natto与MOS联用时内容物中大肠杆菌数量下降（P＜0．05），乳酸杆菌数量显著高于金霉素组（P＜0．05），黏膜中乳酸杆菌数量上升，大肠杆菌数下降，与空白组、金霉素组有显著差异（P＜0．05）；（3）Natto及联用组都显著提高了小肠黏膜的绒毛高度（P＜0．05），但处理组间隐窝深度没有显著差异（P＞0．05），Natto组、1g／kg的MOS组及联用组的绒毛高度／隐窝深度比值显著上升（P＜0．05）。试验说明，纳豆菌和甘露寡糖通过调节肠道内容物及黏膜中微生物区系，降低肠道pH，以维持仔猪肠黏膜正常的形态结构。     

川西北高寒沙地不同年限高山柳林下优势植物碳、氮、磷生态化学计量特征

通过采集川西北高寒沙地不同年限(6、18、24年)高山柳林下3种优势植被藏沙蒿、裂叶独活和镰荚棘豆,分别测定分析3种植被叶片、根部C、N、P化学计量特征变化特征。结果表明:不同年限高山柳林下植被C、N、P含量及其比值间存在显著差异且呈现出不同变化趋势。林下植被C含量整体下降;叶N含量呈上升趋势,根N含量随年限增长而下降;除藏沙蒿外,林下植被P含量变化不显著;C∶N变化范围为1.92~12.86;C∶P为29.18~196.88;不同年限高山柳林下植被N∶P间虽存在差异,但均表现出主要受到P限制,表明该区域植被生长主要受P限制,应注意P养分的适当补充。