土壤砾石的分布及其对水文过程的影响

砾石广泛存在于土壤中。砾石含量和砾石大小随坡度呈增加的趋势,并受到岩性和耕作措施的影响;土壤表层的砾石含量和坡度存在着直线、对数或指数的关系;砾石土/砾质土的水分含量与砾石含量、砾石的来源、大小、孔隙度以及砾石在土壤中存在的位置有关;表土的砾石能增大土壤渗透率、延迟地表积水和径流形成,降低表土水分蒸发,进而减少了土壤和水分的损失。土壤中的砾石不仅改变了土壤的物理特性和化学特性,影响了土壤农学特性,而且制约了一系列的土壤过程。     

应用质谱分析法鉴定桔梗皂甙类成分

对桔梗皂甙的化学成分进行了提取与纯化，首镒利用电喷雾质谱仪对桔梗皂甙类成分进行跟踪分析鉴定。通过对单体化合物各级激发产生碎片峰进行纵向分析及不同单体的横向对比分析，寻找桔梗皂甙类的结构规律，从而鉴定已知结构的皂甙成分，并为未知结构的成分提供信息。     

Distribution and biodiversity of soybean rhizobia in the soils of Shennongjia forest reserve,China

Soil samples were collected at an altitude of 500, 1,060, 1,500, 1,950, 2,400 and 3,100 m, respectively, from Shennongjia, a forest reserve in Hubei province (central China). Their corresponding pHs were 5.50, 4.91, 5.64, 5.28, 5.49 and 4.60. By using a plant trap method, a total of 25 soybean rhizobia were isolated from the soil above an altitude of 1,500 m and all identified to be Sinorhizobium fredii. Their genetic biodiversity was characterized by 16S–23S rDNA internally transcribed spacer (ITS) region polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and random amplification DNA (RAPD) analysis. All the tested strains produced a 2.1 kb 16S–23S rDNA ITS fragment. After digestion with three restriction endonucleases (HaeIII, MspI and CfoI), respectively, great variations in 16S–23S rDNA ITS PCR-RFLP patterns were observed. The tested strains could be differentiated into 11 ITS genotypes. The genotypes of rhizobia were not related to geographical location. Twelve primers were applied to RAPD analysis and a dendrogram was obtained, showing that all the strains (including reference strain S. fredii USDA205) were divided into two diverging groups. Moreover, each group could be further divided into two subgroups. Both RAPD and 16S–23S rDNA ITS PCR-RFLP analysis indicated that a high degree of genetic diversity existed among S. fredii strains isolated from Shennongjia virgin soils. Since Shennongjia is an unexploited forest region in central China and the gene centre of soybean is located in China, the symbiotic genes harboured by these strains may be of great importance and the rich diversity of these strains might contribute to the adaptation of soybean to an alpine environment.     

Effects of habitat fragmentation on Eurasian red squirrel (Sciurus vulgaris) in a forest landscape

We studied the effects of habitat fragmentation, measured as forest stand size and isolation, on the distribution of Eurasian red squirrels (Sciurus vulgaris). Squirrel density was surveyed during four years in 46 forest stands (0.1–500 ha) in a forest landscape in south-central Sweden. The only factor that significantly influenced a density index was the proportion of spruce within a habitat fragment. Neither fragment size nor degree of isolation were significant. Furthermore, none of the interactions with year were significant, suggesting the same pattern in all four years. Thus, the effect of habitat fragmentation in this study seems to be only pure habitat loss, i.e. halving the proportion of preferred habitat in the landscape should result in a halving of the red squirrel population. Therefore, the landscape can be viewed as functionally continuous for the squirrels, although the preferred habitat was divided into fragments. The most likely explanation for the difference between this study and other studies on squirrels that found effects due to habitat fragmentation is a combination of shorter distances and less hostile surroundings in our study area. To identify landscape effects requires multiple studies because single studies usually consider only one landscape.     

Perspective: present pesticide discovery paradigms promote the evolution of resistance – learn from nature and prioritize multi‐target site inhibitor design

For many years, the emphasis of industry discovery programs has been on finding new target sites of pesticides and finding pesticides that inhibit single targets. There had been an emphasis on genomics in finding single targets for potential pesticides. There is also the claim that registration of single target inhibiting pesticides is simpler if the mode of action is known. Conversely, if one looks at the evolution of resistance from an epidemiological perspective to ascertain which pesticides have been the most recalcitrant to evolutionary forces, it is those that have multiple target sites of action. Non‐target‐site resistances can evolve to multi‐target‐site inhibitors, but these resistances can often be overcome by structural modification of the pesticide. Industry has looked at pest‐toxic natural products as pesticide leads, but seems to have abandoned those where they can find no single target of action. Perhaps nature has been intelligent and evolved many natural products that are synergistic multi‐target‐site inhibitors, and that is why natural compounds have been active for millennia? We should be learning from nature while combining new chemistry technologies with vast accrued databases and computer aided design allowing fragment‐based discovery and scaffold hopping to produce multi‐target site inhibitors instead of single target pesticides. © 2019 Society of Chemical Industry     

牛场肥水灌溉冬小麦对不同土层中氨氧化细菌群落多样性的影响

以河北省徐水县长期定位试验田为试验对象,利用末端限制性酶切片段多态性分析(T-RFLP)与构建氨单加氧酶基因(amo A)克隆文库的方法,探究了不同灌溉制度(CK:清水灌溉;CF:无机肥灌溉;T1、T2、T3、T4、T5、T6:不同浓度的牛场肥水灌溉)下,0~20 cm与20~40 cm两个土层中氨氧化细菌(Ammonia-oxidizing bacteria,AOB)的群落结构和多样性。根据AOB的末端限制性酶切片段多态性结果显示,在两个不同的土层中,T1处理(N 105 kg/hm~2,P2O539 kg/hm~2,清水∶沼液=2∶1)的Shannon-Wiener指数和Pielou指数均为最高,T4处理(N 420 kg/hm~2,P2O5156kg/hm~2,清水∶沼液=2∶1)的均为最低,且0~20 cm土层的多样性指数比20~40 cm土层的多样性指数高。表明牛场肥水的浓度同为2∶1时,多次灌溉会降低AOB的群落多样性,且表层土的AOB群落多样性要高于深层土的AOB群落多样性。基于amo A基因的系统发育树显示,0~20 cm土层中AOB主要属于亚硝化螺菌属(Nitrosospira)和亚硝化单胞菌属(Nitrosomanas);20~40 cm土层中AOB则全部属于亚硝化螺菌属(Nitrosospira),说明不同土层之间的氨氧化细菌群落结构存在差异。     

一个通用策略用于构建新型T载体及其应用

由于T栽体能够用于PCR产物的快速克隆且易于操作而受到广泛欢迎.通过选择一个大小合适的媒介DNA片段,采用PCR引物设计,在其两端各引入1个XcmI位点,成功构建了1个重组质粒--pBTMCM,该载体能够非常方便地被限制性内切酶XcmI切割后产生T载体.该载体现在已成功应用于结核分枝杆菌H37Rv Rv0006基因的克隆.该策略由于其通用性因而能被广泛应用.     

Genetic diversity in apricot cultivars based on AFLP markers

A set of cultivars used as genitors in apricot breeding programs aimed at introducing sharka resistance were examined by AFLP molecular marker analysis. The markers obtained indicated that apricot cultivars resistant to sharka were related to the European cultivars, but they potentially share a common ancestor donor of sharka outside of the European group. Segregation of AFLP and RAPD markers has been tested in two progenies of two crosses, one between a resistant and a susceptible cultivar and one between two susceptible accessions. The heterozygozity of families obtained from crosses between resistant and susceptible cultivars is similar to those obtained from other self-incompatible Prunus species. On the other hand, heterozygosity of a progeny obtained from a cross between European susceptible cultivars was very low. The usefulness of the information provided by AFLPs for apricot breeding programs is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

小碎石与细土混合介质的导水特性

含碎石土壤的导水性质研究有利于这种多孔介质水分运动的模拟。本文采用室内定水头法和离心机法分别测定两种质地土壤(壤土、黏壤土)和三种岩性小粒径(2~10 mm)碎石构成的土石混合介质的饱和导水率和水分特征曲线,采用van Genuchten-Mualem模型计算各土石介质的非饱和导水率,分析碎石对土壤导水能力的影响。试验结果显示,风化程度低的碎石对黏壤土具有明显的增大饱和导水率的作用,且碎石含量愈高,增加的效果愈明显;而风化程度高的碎石对土壤结构无明显的改善作用,且对黏壤土具有减小饱和导水率的作用。风化程度低碎石介质的非饱和导水率随土壤水吸力的增加呈现了先大于土壤和土石介质的后迅速减小到低于土壤和土石介质的变化过程。风化程度低的河卵石和风化程度高的粉泥页岩碎屑分别构成的土石介质的非饱和导水率较土壤的低,而风化程度中等的片麻状花岗岩碎块构成的土石介质的非饱和导水率较土壤的高。近饱和状态下,碎石含量高的土石介质的非饱和导水率也相应的高,而较大的土壤水吸力下,土石介质的非饱和导水率呈现随碎石含量的增大而减小变化趋势。试验结论可为含碎石土壤水分平衡研究提供参考。     

提高转HSA基因小鼠效率的研究

将无基因的序列CIT987SK-384D8(30号)和结构特异的内切酶基因hFEN1穴36号雪与HSA的cDNA(26号)进行混合注射来制备转HSA小鼠动物模型,旨在提高转HSA基因效率。结果表明:无基因的序列CIT987SK-384D8对HSA的整合基本无影响穴P>0.05雪,结构特异的内切酶基因hFEN1可以显著提高转HSA基因效率穴P<0.01雪。