三峡库区淌里滑坡变形特征及影响因素分析

滑坡监测主要采用地表位移GPS监测和滑体深部位移监测等方法。根据多年滑坡变形、库区降雨、库区水位变化等相关资料,分析了三峡库区淌里滑坡的空间变形特征,并研究了降雨和库区水位两个因素对滑坡变形的影响。该滑坡变形区呈牵引式变形特征,多年位移监测数据曲线呈阶跃性特征,与降雨过程具有一定的相关性,同时库水位的大幅变动对滑体变形的节奏也产生一定影响。滑体变形对水位下降的情况较为敏感,尤其当水位在一段时间内按一定速率持续宽幅下降时对变形区的稳定性影响更为强烈。     

三峡库区典型滑坡监测及治理措施研究

根据三峡库区典型滑坡火石滩滑坡的结构及变形特征，分析滑坡形成的原因。对该滑坡进行大地形变监测、地下水位监测、滑体深部位移监测和宏观监测；依据监测资料并考虑到未来三峡水库蓄水，认为火石滩滑坡目前处于潜在不稳定状态。滑坡体在饱水及水库蓄水后，将处于临界蠕滑或失稳状态。结合滑坡体实际对滑坡防治进行初步研究，建议采用回填压脚支档为主、辅以排水的综合治理措施。     

三峡库区甘家院子滑坡稳定性预测与验算

三峡库区云阳县甘家院子滑坡是由H1、H2、H3滑坡体组成的滑坡群，类型复杂，影响范围甚广。在深入分析了滑坡地质特征、结构特征和变形特征的基础上，对滑坡就蓄水以后滑坡体的变形、失稳形式作出预测，最后采用传递系数法验算滑坡体整体稳定和局部稳定性，所得结果为滑坡的治理与防治工程提供依据。同时计算结果表明，该滑坡目前处于稳定状态，在库水位作用下或遭遇长时间高强度的暴雨时，滑坡可能整体失稳，与预测结果完全吻合。     

三峡库区某滑坡稳定性分析及工程治理

在研究了三峡库区某滑坡的工程地质条件及滑坡体特征的基础上,分析了该滑坡成因机制和失稳因素。考虑到未来三峡蓄水位的变化,结合不同工况对该滑坡进行了稳定性计算,针对计算结果,提出并设计了采用抗滑桩支挡与监测工程相结合的综合工程治理方案。     

降雨和库水位升降对滑坡的影响

滑坡是三峡库区重要地质灾害之一,影响滑坡稳定性的因素有很多。针对降雨和库水位升降以水泥厂滑坡为例,运用自动化远程监测其变形和该区域降雨量,通过数据整理、分析,掌握降雨和库水位升降对滑坡变形的影响状况。结果表明：在监测期间,个别时间段滑坡变形加剧是降雨和库水位升降共同作用的结果,个别时间段降雨、库水位升降分别为滑坡变形加剧的主导因素,降雨对滑坡变形的影响表现出一定的滞后效应,滞后期一般为7～15d。监测表明,目前滑坡仍处于变形阶段,且向SE方向旋转滑移,但趋势有所减缓。通过对该滑坡的变形监测,可以定量分析和描述滑坡的运动状态,对三峡库区其它类似滑坡的研究具有重要的指导意义。     

三峡库区某退水滞后型滑坡渗流及稳定性分析

三峡库区自2003年蓄水以来,库区水岩作用引发了水库岸坡失稳等地质灾害,其中水库岸坡破坏出现在库水位上升期的占40%~49%,出现在水位消落期的约占30%,而有些大型滑坡会发生在库水位达到最大值后的快速消落期。本研究以三峡库区某退水滞后型滑坡为例,结合2016年1—6月三峡水库水位的实际运行情况并联合降雨,利用数值模拟的方法模拟其渗流场变化并进行稳定性计算。研究结果表明:库水位下降并叠加降雨的情况下,对滑坡的稳定性不利,当库水位下降速率达到1.0 m/d且叠加降雨时,滑坡的稳定性最差,此时为最不利工况;在5种工况条件下,滑坡的稳定性有所降低,但稳定性数值均大于1.05,说明滑坡仍处于基本稳定状态。     

模糊数学理论和数值分析在滑坡评价中的应用

根据三峡库区典型的弱透水型滑坡——白家包滑坡地质资料和监测数据,运用模糊数学理论和数值分析法对滑坡稳定性进行了定性和定量评价。模糊数学理论评价结果显示白家包滑坡处于欠稳定状态;数值分析模拟结果显示白家包滑坡受库水位下降影响较大,特别是在库水位下降和强降雨叠加情况下稳定性下降明显,处于欠稳定状态。监测点监测结果证明采用这两种方法的评价结果具有一致性,且与实际情况相符。     

三峡库区动水压力型土质滑坡排水管布置优化——以卧沙溪滑坡为例

[目的]为降低动水压力型滑坡体内的动水压力,提高其稳定性,采取布设水平排水管的措施对该类型滑坡进行治理,并对排水管的布设方案进行优化,为同类滑坡的加固设计以及获得高效合理的排水管布设方案提供参考。[方法]利用土体级配曲线,采用间接方法近似确定滑体土土—水特征曲线,并尝试通过FredlundXing函数模型预测获得滑体土非饱和渗透函数曲线。采用均匀设计方法、有限元、神经网络和遗传算法相结合的综合集成方法开展排水管布设方案优化研究。[结果]获得了卧沙溪滑坡最优的排水管布设方案为:管长L为26.6m,间距D为6.88m,倾斜角θ为7.3o。[结论]采用该排水方案加固后的滑坡安全系数为1.101,大于设计安全系数1.10,满足滑坡加固安全与经济的要求。     

三峡库区某滑坡变形影响因素分析

根据三峡库区某滑坡5年左右的GPS位移监测以及降雨量、库水位监测数据,选取降雨和库水位两个因素研究了其对滑坡变形的影响。结果表明:降雨的入渗增加了滑体重量、软化了岩土体、润滑了滑带与滑床的接触面,会降低滑坡的稳定性;库水位的上升一般对岩土堆积层滑坡的稳定性无明显不利影响,而其下降却使滑坡变形加速;两者对滑坡变形的影响均表现出一定的"滞后效应",滞后期一般为5~10 d。     

库水位升降对李家坡滑坡稳定性的影响

以三峡库区巫山李家坡滑坡为研究对象,依据勘察资料和试验资料等,应用地学软件GeoStudio中的SEEP模块和SLOPE模块建立相应的模型,用实时监测数据对模型进行校正,用校正后的模型模拟库水位以不同速率升降对滑坡稳定性的影响。研究结果表明:水库型滑坡稳定性受库水位升降速率影响明显,稳定性变化主要受静水压力、动水压力、库水浮托力、岩土体物理力学性质变化等共同影响,变化趋势由占主导地位的影响因素决定。     

Potential of wild species for genetic enhancement of some semi-arid food crops

Discovery and incorporation of genes from wild species provide means to sustain crop improvement, particularly when levels of resistance in the cultigens are low and virulent strains of pests and pathogens overcome the host plant resistance. The extent of utilization and the potential of the wild genepool for genetic enhancement were reviewed in five important food crops viz. sorghum, pearl millet, chickpea, pigeonpea and groundnut grown in the semi-arid tropics. Introgression from compatible wild germplasm in the primary gene pool resulted in transfer of new cytoplasmic male sterility systems in pearl millet and pigeonpea, development of high protein, cleistogamous flower and dwarf pigeonpea lines and foliar disease resistant groundnut cultivars. Utilization of wild species in secondary and tertiary gene pools has been generally limited due to sterility, restricted recombination or cross incompatibility. Nevertheless, these species are extremely important as they contain high levels of resistance to several important biotic and abiotic stresses. Several of them, like those belonging to the Parasorghum section and the rhizomatous Arachis species are sources of multiple resistances and hold great promise to sustain crop productivity.     

“绿色革命”以来大气CO2浓度升高对C3作物营养品质的影响

自20世纪60年代"绿色革命"以来,育种技术和农耕技术的发展促进了农作物产量的大幅提升,然而作物的营养品质出现下降趋势。在相似的遗传背景下,大气CO_2浓度升高会使单位体积农作物产品的营养元素含量下降,因此"绿色革命"至今,农作物产品的营养元素下降可能受大气CO_2浓度升高影响。通过植物生长箱模拟"绿色革命"初期和目前的大气CO_2浓度水平(310μmol/mol和400μmol/mol),针对主要C_3作物水稻、小麦和大豆,研究"绿色革命"以来大气CO_2浓度升高对其籽粒的C、N、Fe、Zn元素含量的影响,结果表明:CO_2浓度升高对3种作物籽粒的C元素含量几乎没有影响,变化幅度在±1.5%之间;籽粒的N、Fe、Zn元素含量普遍呈现下降趋势,但均未达到显著水平。     

Faculty positions:Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications     

Collection and preliminary evaluation of native turfgrass accessions in Italy

Despite a raising interest on turfs in Italy, all theavailable varieties of this kind in the Country are of foreign origin, and areoften poorly adapted to the prevailing climatic conditions. This prompted tobegin a collection activity of indigenous turfgrass species, with the ultimategoal of identifying promising materials for future breeding based on localgenetic resources. The collection was carried out in three areas of Italy, viz.the northern Po Plain, the coastal region of Liguria, and the island of Sardiniathat are characterised, respectively, by subcontinental, warm temperate, andtypical Mediterranean climate. Altogether, 141 sites were visited, yielding 226accessions belonging to eight species of potential interest for turfs:Poa pratensis, Poa trivialis,Festuca rubra, Festuca arundinacea,Lolium perenne, Agrostis stolonifera,Agrostis tenuis, and Cynodon dactylon,this last being a warm-season grass. Poa pratensis andCynodon dactylon were mostly collected in northern Italyand Sardinia, respectively, whereas Festuca arundinacea andLolium perenne were rather ubiquitous. The collection sitesranged from 0 to 1040 m asl, but sites over 750 m wereonly visited in the inner part of Sardinia. All the accessions, collected aswhole plants, were transplanted at Lodi, northern Italy, where they are beingevaluated. Their preliminary evaluation for traits of importance for turf use,such as sward colour and overall quality, highlighted the great variation andthe occurrence of interesting accessions in all species. Other characters wererecorded, bearing specific importance in individual species, and in all casespromising accessions were identified. The germplasm of Festucarubra, Festuca arundinacea, and Loliumperenne proved highly infected by endophytic (symbiotic) fungi of thegenus Neotyphodium.     

Leaf position and genotype differences for mineral element concentrations in sorghum grown on tropical acid soil 1

Mineral element deficiencies and toxicities are common problems associated with sorghum [Sorghum bicolor (L.) Moench] production on acid soils. To better understand some of the mineral element problems and the analysis of plant tissue of sorghum plants grown on acid soils, four sorghum genotypes were grown on an acid Oxisol at Carimagua, Colombia limed with dolomite at 2 and 6 Mg ha^‐1.

Samples for mineral element analyses were obtained from leaves at different positions on the four genotypes. Concentrations of P and Mg were highest in the flag leaf (Leaf No. 1) and decreased as the position on the plant declined from the top of the plant for plants grown at 2 Mg lime ha^‐1. Similar decreases in P, Mg, K, and Zn concentrations occurred in plants grown with 6 Mg lime ha^‐1. Concentrations of Ca, S, Si, Mn, Fe, Cu, and Al increased as leaf position declined from the flag leaf for plants grown at 2 and 6 Mg lime ha^‐1. The higher lime supply enhanced Ca and reduced Mn and Fe concentrations in leaves. Differences in mineral element concentrations for the four genotypes used were fairly extensive. The elements to show the greatest range among genotypes were Al and Si and the elements to show the least range among genotypes were P, K, and S. Care should be used in collecting leaf samples for plant analysis and genotypic differences for accumulation of mineral elements should be considered in interpretation of results.     

Short-term variation in the concentration of selected ions within individual tropical rainstorms

Rainwater was collected at the campus of the University of Brunei Darussalam in Bandar Seri Begawan, Brunei Darussalam, using a funnel-in-bottle sampler. Polypropylene bottles were changed at intervals during rainstorm events. The pH and conductivity were determined immediately after collection on aliquots of the sample. Samples were refrigerated at 5°C for subsequent chemical analysis. Analyses for Na, Mg, Ca, Zn and Fe were carried out by means of inductively coupled plasma atomic emission spectroscopy (ICP-AES); Cu and Mn were analysed by graphite furnace atomic absorption spectroscopy (GFAAS); K was analysed using flame atomic emission spectroscopy (FAES); and Cl^–, NO₃ ^– and SO₄ ^2– were analysed by ion chromatography (IC). Concentration versus time profiles are reported for three rainstorm events. All ions exhibited a decrease in concentration during the rainstorm. The first sample contained the highest concentration of ions, consistent with a first-flush effect. The contribution of the initial stages of the shower to the total quantity of ion deposited during the entire rainstorm is quite overwhelming; in many cases 20 to 30% of the mass was deposited in less than 5% of rainstorm duration. On the other hand, the pH and conductivity variation during rainstorms did not exhibit a consistent pattern.     

Leaf litter selection by detritivore and geophagous earthworms

Summary Litterbag experiments with 10 different kinds of leaf litter showed that detritivore (Lumbricus species) and geophagous (Aporrectodea species) earthworms prefer certain litter types over others, since different numbers of worms were found below the litter after 50–52 days of exposure in a pasture. The detritivores preferred Fraxinus, Tilia, and predecomposed Ulmus and Fagus litter to Fagus litter and paper, while geophages preferred Tilia litter to Alnus and Ulmus litter, so that the two groups of earthworms showed different preferences. The detritivores seemed to be more selective than the geophages. The palatability of the litter was examined in relation to the C: N ratio, the lignin concentration and the initial and final polyphenol concentration. The numbers of detritivores were significantly correlated with the C: N ratio and the final polyphenol concentration, so that selection of litter seems to be related to palatability. The numbers of geophages were not significantly correlated with any of the parameters for palatability. The disappearance of litter after 50–52 days appeared to be due to detritivore activity, since the numbers found below the litter were positively and significantly correlated with the litter disappearance. There was no significant correlation with geophage activity. This indicates that detritivores use litter as food, and therefore influence the composition of the litter layer.     

The 5S rRNA gene diversity in the genus <Emphasis Type="Italic">Secale</Emphasis> and determination of its closest haplomes

We analyzed 127 rDNA sequences (5S DNA units) obtained from 23 seed accession samples from more or less 10 taxa in wild and cultivated rye, genus Secale L. The sequences fell into two known groups, here assigned to two unit classes, viz. long R1 and short R1 (designations to reflect on R haplome of rye). The different taxa could not be fully differentiated based on the 5S DNA units. We searched for 5S DNA sequences from known unit classes most closely similar to the long R1 and the short R1. One set with the long R1 unit class contained sequences of the long P1 unit class from Agropyron (P haplome) and from Kengyilia (StYP haplome), long J1 from Thinopyrum (J haplome), whereas the set with the short R1 included the long S1 from Pseudoroegneria (St haplome) and Kengyilia (StYP haplome), the short J1 from Thinopyrum (J haplome) and the short V1 from Dasypyrum (V haplome). Each of the two sets was analyzed separately by maximum likelihood (ML) phylogenetic analysis from which we were able to infer that the 5S DNA units of Secale differentiated in a non-clock fashion and followed the HKY substitution model in the gene tree with the long R1 unit class and the HKY + G in the gene tree with the short R1 unit class. A complementary Bayesian analysis yielded identical tree topologies to the ML ones for each of the two sequence sets. In the tree with the long R1 units the long P1 and long J1 unit classes were closest to the long R1 unit class, whereas in the tree with the short R1 units the long S1 and short J1 unit classes were closest to the short R1 unit class, indicating possibly a close relationship between the St, J and R haplomes.     

Nematode succession and microfauna-microorganism interactions during root residue decomposition

The quality of plant material affects the vigor of the decomposition process and composition of the decomposer biota. Root residues from hairy vetch (Vicia villosa Roth), rye (Secale cereale L.) and vetch+rye, packed in litterbags were placed in pots of soil at 15 C and the content of the bags was analyzed after 2, 4, 8 and 12 weeks. Bacterial biomass did not differ between residues with contrasting composition. Among bacterivores groups of nematodes that require high bacterial production dominated in fast decomposing resources whereas flagellates with smaller requirements prevail in slower decomposing resources. Biomass of bacterial feeding nematodes correlated positively with early phase (0-2 wk) decomposition that increased in the order: rye< vetch+rye<vetch. Bacterial biomass therefore seems to be under top-down (predation) control during early decomposition. In contrast, the fungal biomass differed between resources with highest values for rye. Moreover, this increase in fungal biomass occurred later during succession and was correlated with decomposition activity for rye in that period. Fungal biomass therefore seems to be under bottom-up (resource) control. The composition of the nematode assemblages (composed of 25 taxa) showed a clear relationship to initial plant resource quality as well as decomposition phase. Early successional microbivorous nematodes vary according to resource quality with demanding bacterivores+predators (Neodiplogasteridae) dominating in vetch and less demanding bacterivores (Rhabditidae) and fungivores (Aphelenchus) being equally common in vetch and rye. Later in the succession (2-4 wk) bacterivorous Cephalobidae and fungivorous Aphelenchoides prevailed similarly on the different root materials whereas bacterivorous protozoa and the amoebal fraction thereof dominated in rye. At week 12 no species dominated the nematode assemblages that were similar between the resources. The differences between nematode assemblages among plant resources at 2 week were similar to the results of a field study sampled after 6 weeks with the same soil and plant resources. This lends support to the relevance of the successional patterns observed in this incubation study.     

Cycling of extracellular DNA in the soil environment

Upon entering the soil environment, extracellular DNA is subjected to dynamic biological, physical, and chemical factors that determine its fate. This review concerns the fate of both recombinant and non-recombinant sources of DNA. A schematic of DNA cycling coupled with genetic transformation is presented to understand its behavior in soil. Extracellular DNA may persist through cation bridging onto soil minerals and humic substances, be enzymatically degraded and restricted by DNases of microbial origin, and/or enter the microbial DNA cycle through natural transformation of competent bacteria. Lateral gene transfer may disseminate DNA through the microbial community. An understanding of DNA cycling is fundamental to elucidating the fate of extracellular DNA in the soil environment.