Matric potential evaluations and measurements for gelled substrates

A new method for evaluating the matric potential of gelled media has been developed. The method allows the derivation of the matric potential as a limit of a series of measurements of water potential values from gelled media prepared without added components, from agar powders progressively cleaned of mineral impurities. Three commercial agar brands were tested, and for these the matric potential was found to contribute only between 1 and 2% of their total water potential. Thermodynamic features relating matric and osmotic potentials are described. New hypotheses for understanding the water flux mechanism from gel to tissue cultured explants are discussed. Movement of water along polymeric chains is postulated to be a facilitated step in comparison with bulk movement.     

Graph decompositions for demographic loop analysis

A new approach to loop analysis is presented in which decompositions of the total elasticity of a population projection matrix over a set of life history pathways are obtained as solutions of a constrained system of linear equations. In loop analysis, life history pathways are represented by loops in the life cycle graph, and the elasticity of the loop is interpreted as a measure of the contribution of the life history pathway to the population growth rate. Associated with the life cycle graph is a vector space -- the cycle space of the graph -- which is spanned by the loops. The elasticities of the transitions in the life cycle graph can be represented by a vector in the cycle space, and a loop decomposition of the life cycle graph is then defined to be any nonnegative linear combination of the loops which sum to the vector of elasticities. In contrast to previously published algorithms for carrying out loop analysis, we show that a given life cycle graph admits of either a unique loop decomposition or an infinite set of loop decompositions which can be characterized as a bounded convex set of nonnegative vectors. Using this approach, loop decompositions which minimize or maximize a linear objective function can be obtained as solutions of a linear programming problem, allowing us to place lower and upper bounds on the contributions of life history pathways to the population growth rate. Another consequence of our approach to loop analysis is that it allows us to identify the exact tradeoffs in contributions to the population growth rate that must exist between life history pathways.     

长白山次生针阔混交林叶凋落物中有机物分解与碳、氮和磷释放的关系

采用分解袋法,研究了长白山次生针阔混交林内9种树种叶凋落物34个月的分解过程.结果表明:在次生针阔混交林中,不同树种叶凋落物的初始N和P浓度存在很大差异,叶凋落物分解速率(k)与初始N浓度和C/N显著相关.有机物剩余百分率与C剩余百分率呈显著的线性正相关关系,与N和P剩余百分率之间呈显著的二项式回归关系. N和P剩余百分率在初期阶段随有机物分解而增加,达到峰值后逐渐降低. 随着有机物剩余百分率的下降,C/N和C/P均呈逐渐降低趋势,各种叶凋落物之间C/N和C/P的差异逐渐减小,分解末期分别趋近于23和350. 随有机物剩余百分率的降低, N/P变化不明显,当有机物剩余百分率低于25%时,不同树种叶凋落物之间N/P差异显著下降. 有机物剩余百分率可用来预测C、N和P的剩余百分率.      

太行山山地森林群落植物区系与地理格局——基于植物群落清查数据

太行山区位于黄土高原与华北平原之间,是我国生物多样性保护的重要优先区之一.本文以广义太行山涉及的108个行政县域为研究区域,基于太行山山地森林群落植物清查数据,系统分析了太行山山地森林群落的科属特征、区系组成、植物多样性地理格局及其丰富度热点地区.结果表明: 调查的778个样地得到太行山山地森林群落种子植物共计100科447属963种,其中,裸子植物3科7属12种,被子植物97科440属951种,生活型以草本植物占优势(71.1%);科的分布区类型以热带分布(38%)和温带分布(24%)为主,属的分布区类型以温带成分占主导(68.7%);太行山山地森林群落植物多样性的水平分布格局呈由西南向东北逐渐递增的趋势,群落物种多样性与经纬度均呈正相关关系,但不同生活型植物的多样性格局不相一致,草本植物多样性与经纬度呈正相关,而木本植物多样性与经纬度则无明显相关性;在垂直梯度上,太行山山地森林群落植物丰富度呈单峰分布,集中分布在400~1800 m的低中海拔地带,在1000~1200 m丰富度最高;基于群落清查数据绘制太行山山地森林群落植物丰富度分布图,鉴别出小五台山、云台山、太岳山、王屋山、中条山等山地为植物丰富度热点地区,应列入太行山优先保护的重点规划区域.     

The potential of fish production based on periphyton

Periphyton is composed of attached plant andanimal organisms embedded in amucopolysaccharide matrix. This reviewsummarizes research on periphyton-based fishproduction and on periphyton productivity andingestion by fish, and explores the potentialof developing periphyton-based aquaculture.Important systems with periphyton arebrush-parks in lagoon areas and freshwaterponds with maximum extrapolated fish productionof 8 t ha^–1 y^–1 and 7 t ha^–1y^–1, respectively. Experiments with avariety of substrates and fish species havebeen done, sometimes with supplemental feeding.In most experiments, fish production wasgreater with additional substrates compared tocontrols without substrates. Colonization ofsubstrates starts with the deposition oforganic substances and attraction of bacteria,followed by algae and invertebrates. Afterinitial colonization, biomass density increasesto a maximum when competition for light andnutrients prevents a further increase. Often,more than 50% of the periphyton ash-free drymatter is of non-algal origin. Highest biomass(dm) in natural systems ranges from 0 to 700g m^–2 and in aquaculture experiments wasaround 100 g m^–2. Highest productivity wasfound on bamboo in brush-parks (7.9 gC m^–2 d^–1) and on coral reefs (3 gC m^–2 d^–1). Inorganic and organicnutrients stimulate periphyton production.Grazing is the main factor determiningperiphyton density, while substrate type alsoaffects productivity and biomass. Better growthwas observed on natural (tree branches andbamboo) than on artifical materials (plasticand PVC). Many herbivorous and omnivorous fishcan utilize periphyton. Estimates of periphytoningestion by fish range from 0.24 to 112 mg dm(g fish)^–1 d^–1. Ingestion rates areinfluenced by temperature, fish size, fishspecies and the nutritional quality of theperiphyton. Periphyton composition is generallysimilar to that of natural feeds in fishponds,with a higher ash content due to the entrapmentof sand particles and formation of carbonates.Protein/Metabolizable Energy (P/ME) ratios ofperiphyton vary from 10 to 40 kJ g^–1.Overall assimilation efficiency of fish growingon periphyton was 20–50%. The limited work onfeed conversion ratios resulted in valuesbetween 2 and 3. A simple simulation model ofperiphyton-based fish production estimates fishproduction at approximately 2.8 t ha^–1y^–1. Together with other food resources infishponds, total fish production with thecurrent technology level is estimated at about5 t ha^–1 y^–1. Because grazingpressure is determined by fish stocking rates,productivity of periphyton is currently themain factor limiting fish production. Weconclude that periphyton can increase theproductivity and efficiency of aquaculturesystems, but more research is needed foroptimization. Areas for attention include theimplementation and control of periphytonproduction (nutrient levels, substate types andconformations), the ratio of fish to periphytonbiomass, options for utilizing periphyton inintensive aquaculture systems and with marinefish, and possibilities for periphyton-basedshrimp culture.     

Soil ingestion estimates for use in site evaluations based on the best tracer method

This paper develops a novel methodology, the Best Tracer method (BTM), that substantially overcomes the principal limitations (intertracer inconsistencies, and poor precision of recovery) of estimating soil ingestion by specific soil‐based tracers in massbalance studies. The BTM incorporates a biological and statistical framework that improves precision of recovery of tracer estimates, markedly reducing input‐output misalignment error resulting from a lack of correspondence between food tracer input and fecal tracer output.

This method is then used to re‐estimate the soil ingestion distribution of previously published soil ingestion estimates from two children studies (Calabrese et al. 1989; Davis et al., 1990) and one adult study (Calabrese et al., 1990). Revised estimates of soil ingestion are provided for each study. In addition, the results from the two children's studies are combined to form a single estimate of the soil ingestion distribution. These collective findings result in more reliable quantitative estimates of soil ingestion than trace element specific estimates, as well as providing improved understanding of current published soil ingestion studies, and improved methods that will enhance the design and interpretation of future soil ingestion studies.

With respect to children, the data indicate that the Calabrese et al. (1989) study provides the most reliable estimates of soil ingestion based on the estimated precision of recovery. However, estimates for the combined data of the Calabrese et al. (1989) and Davis et al. (1990) studies include all available children's data from mass balance studies, and thus provide more robust estimates. The collective data suggest that the median child in these studies ingested 30–40 mg/day of soil, while the upper 95% estimate is approximately 200 mg/day. Current data are insufficient to distinguish the children's soil ingestion distribution from that of adults. The revised and improved estimates of soil ingestion for children and adults have important implications for contaminant exposure estimates used in site evaluation risk assessment procedures.     

Breaking the loop: oxytocin as a potential treatment for drug addiction

Drug use typically occurs within a social context, and social factors play an important role in the initiation, maintenance and recovery from addictions. There is now accumulating evidence of an interaction between the neural substrates of affiliative behavior and those of drug reward, with a role for brain oxytocin systems in modulating acute and long-term drug effects. Early research in this field indicated that exogenous oxytocin administration can prevent development of tolerance to ethanol and opiates, the induction of stereotyped, hyperactive behavior by stimulants, and the withdrawal symptoms associated with sudden abstinence from drugs and alcohol. Additionally, stimulation of endogenous oxytocin systems is a key neurochemical substrate underlying the prosocial and empathogenic effects of party drugs such as MDMA (Ecstasy) and GHB (Fantasy). Brain oxytocin systems exhibit profound neuroplasticity and undergo major neuroadaptations as a result of drug exposure. Many drugs, including cocaine, opiates, alcohol, cannabis, MDMA and GHB cause long-term changes in markers of oxytocin function and this may be linked to enduring deficits in social behavior that are commonly observed in laboratory animals repeatedly exposed to these drugs. Very recent preclinical studies have illustrated a remarkable ability of exogenously delivered oxytocin to inhibit stimulant and alcohol self-administration, to alter associated drug-induced changes in dopamine, glutamate and Fos expression in cortical and basal ganglia sites, and to prevent stress and priming-induced relapse to drug seeking. Oxytocin therefore has fascinating potential to reverse the corrosive effects of long-term drugs abuse on social behavior and to perhaps inoculate against future vulnerability to addictive disorders. The results of clinical studies examining intranasal oxytocin effects in humans with drug use disorders are eagerly awaited. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.     

Genetic analysis of seven Italian horse breeds based on mitochondrial DNA D‐loop variation

To understand the origin and genetic diversity of Italian horses, mitochondrial DNA D‐loop sequences were generated for 163 horses from seven breeds. Sequence analysis of a 480‐bp segment revealed a total of 84 haplotypes with 57 polymorphic sites, indicating multiple maternal origins and high genetic diversity. Comparison of the haplotypes with the equine mtDNA haplotype/haplogroup nomenclature showed a haplogroup distribution in the Italian breeds more similar to that found in the Middle East breeds than in the European breeds, probably due to the economic and cultural relationship with the Middle East in the past centuries.     

多元统计方法在节肢动物群落分析中的应用

近年来有关节肢动物群落的研究报道较多,而传统的、简单的多样性指数分析远远不能满足对高通量群落数据的挖掘。采用多元统计方法可以较好地分析群落数据。其中,在研究某一处理的长期效应时,主响应曲线是一种经典的多元分析方法;而非度量多维尺度分析具有能处理较大量的数据且常能以低维排序图反映结果的优点,是一种具有广泛应用前景的排序技术。本文以Bt棉与非Bt棉不同比例混作棉田的节肢动物群落为例,详尽地介绍了主响应曲线和非度量多维尺度在节肢动物群落分析中的应用。     

基于限制因子分析的耕地质量提升潜力分区

以宝鸡市为研究区,从地类图斑尺度,识别了宝鸡市耕地质量主导限制因子类型,根据限制因子提升潜力的空间分布特征,划分了耕地质量提升潜力分区,探讨了不同潜力分区耕地质量的提升措施.结果表明:宝鸡市耕地质量限制因子主要为单因子限制型,包括土层限制、有机质限制和灌溉限制,共占宝鸡市耕地总面积的66.11%;耕地质量提升潜力处于中等水平,且呈现北高南低的分布趋势,在空间上表现出一定的集聚特点;宝鸡市334个行政村耕地质量提升潜力较高且呈“HH”型分布(Ⅰ级区),可加大该区域土地整治工程力度,以提高区域耕地质量整体水平;宝鸡市中部地区的耕地质量提升措施应着重考虑增加有效土层厚度、提高土壤有机质含量和改善农用地灌溉条件;北部地区还应加强对土壤侵蚀的改良,南部地区应采取有效措施减小岩石露头度和地形坡度对耕地质量的影响.     

A tier system for developmental toxicity evaluations based on considerations of exposure and effect relationships

The backlog of untested chemicals and the rate at which new substances enter the marketplace exceed our capacity for developmental effects testing by standard in vivo methods. However, conservative use of two observations in a manner consistent with present day understanding of abnormal developmental biology can more accurately focus attention and resources on those agents in greatest need of complex testing for effects on in utero development. These two observations are 1) most chemicals are no more toxic to embryonic development than they are to adult homeostasis and 2) most human exposure to chemicals is de minimus, i.e., so small that it is inconsequential. Recently devised in vitro assays to quantitatively rank chemicals according to their developmental hazard index, when used in conjunction with more conventional in vivo methods and appropriate considerations of exposure, permit evaluation of a significantly larger number of chemicals than is currently achieved. The methods described apply a tier approach to establish testing priorities that markedly reduce the time, cost, and number of laboratory animals needed for evaluation of developmental toxicity.     

The rising level of medical student debt: potential risk for a national default

At the turn of the 20th century, mostly as a result of the Flexner report, medical education changed dramatically by establishing a scientific basis for the study of medicine within the institutions of the major universities. There have been major and dramatic changes in medicine during the past 80 years that have improved medical education in the United States, but these changes have also placed major economic strains on students who have educational debts. If medicine is a social responsibility to the public, then the public should share the responsibility of identifying and supporting new approaches to funding and financially managing the teaching of future physicians. There is no universal solution because there are various approaches institutions may take to structure these financial responsibilities. This article describes trends in medical student educational debt, identifies the financial needs of medical students, and proposes ways of addressing those needs to avert a possible national financial crisis among medical students. We must invest in medical students because they will be the leaders we need to help care for our society and our own families in the next century.     

16S rDNA analysis reveals low microbial diversity in community level physiological profile assays

The metabolic diversity of microbial communities is fundamental for the multiple soil functions mediated by microorganisms. Community level physiological profiles (CLPPs) based on sole C source oxidation have been used as a fast and reproducible tool to study soil microbial functional diversity because the utilisation of available carbon is the key factor governing microbial growth in soil. Our aim was to assess the phylogenetic affiliation of the microorganisms responsible for C consumption after inoculating Biolog plates. For this purpose, two semi-arid Mediterranean forest soils with significantly different patterns of C consumption and microbial community structure were used. Following the inoculation of the Biolog plates, suspensions from seven wells were sampled after 1, 2 and 7 d of incubation. DNA was extracted and the microbial communities analysed by polymerase chain reaction followed by denaturing gradient gel electrophoresis (PCR-DGGE) and sequencing of excised bands. Despite major differences in the microbial communities of the soils studied, their DGGE banding patterns after incubation were similar for all the analysed C source suspensions. Microorganisms belonging to beta-Proteobacteria (Ralstonia sp. and Burkholderia sp.) and alpha-Proteobacteria (Rhizobium sp.) were dominant. These opportunists had a competitive advantage under the conditions at which the CLPPs were analysed. This study reveals that significantly different CLPP patterns can be generated on the basis of only 3-4 genera, as reflected by PCR-DGGE analysis. Also for this reason, CLPPs based on incubations of soil suspensions should just be used as a screening method and always be accompanied by other techniques for community analysis.     

The impact of plant chemical diversity on plant–herbivore interactions at the community level

Oecologia - Understanding the role of diversity in ecosystem processes and species interactions is a central goal of ecology. For plant–herbivore interactions, it has been hypothesized that...     

基于Voronoi图的群落优势树种种内种间竞争

在浙江天目山国家级自然保护区内,选择典型常绿阔叶林设置样地,样地大小100m×100m。用全站仪测定每株树木坐标(x,y,z)。首先,用优势度分析法确定群落优势树种。其次,提出基于Voronoi图的V_Hegyi竞争指数,并对Hegyi、APA和V_Hegyi三种竞争指数进行比较分析。最后,采用V_Hegyi竞争指数分析常绿阔叶林的种内、种间竞争关系。结果表明:常绿阔叶林群落共有11个优势树种即细叶青冈(Cyclobalanopsis myrsinaefolia)、青冈(Cyclobalanopsis glauca)、短尾柯(Lithocarpus brevicau-datus)、豹皮樟(Litsea coreana)、白栎(Quercus fabri)、天目木姜子(Litsea auriculata)、黄连木(Pistacia chinensis)、榉树(Zelkovaschneideriana)、杉木(Cunninghamia lanceolata)、枫香(Liquidambar formosana)和黄檀(Dalbergia hupeana)。比较分析认为,V_Hegyi竞争指数既克服了用固定半径圆确定竞争单元的尺度不统一缺陷,又可进行种内、种间竞争分析,并保持竞争排序的稳定性,因此是优于Hegyi和APA的更合适的竞争指数,所以选择V_Hegyi竞争指数进行优势树种竞争分析。常绿阔叶林优势树种的种内竞争比种间竞争激烈。种内竞争最激烈的优势树种细叶青冈、青冈和短尾柯与其它优势树种的种间竞争强度也是最高的。反之,种内、种间竞争都较弱的优势树种包括豹皮樟、白栎、天目木姜子、黄连木、榉树、杉木、枫香和黄檀。多数优势树种存在1个主要竞争树种,很少有超过3个以上的情形。细叶青冈是群落最占优势的树种,具有最强烈的种内竞争。同时,也是所有其它优势树种的最大竞争者。     

Surface plamon resonance imaging of DNA based biosensors for potential applications in food analysis

The adsorption processes of oligonucleotides immobilised onto suitable photolithographic patterned gold substrates have been investigated in aqueous buffer solution by using a home made surface plasmon resonance (SPR) imaging equipment. A rapid self-assembled method for the construction of DNA chips to be used in SPR imaging experiments have been followed. The immobilised DNA molecules (probes) adopted in our SPR experiments anchored to a gold surface via thiol group were 5'thiol-modified containing a (CH(2))(15) tail. The hybridisation processes taking place with its complementary sequence have been observed and characterized by monitoring phenomena by a SPR imaging system. The two analysed oligonucleotides (probes and target) are of interest in plant gene biotechnological application and differing for the presence at the 5'-end of a poly T16 spacer. Dynamic investigation of smallest changes in SPR imaging pictures performed in liquid phase in the presence of DNA complementary probes have been performed. Quantitative information in terms of threshold of sensitivity has been extracted by using a specific images treatment.     

基于mRNA水平的差异表达基因筛选技术

随着分子生物学技术的深入发展,基因组研究重点已经由基因组测序转向基因功能鉴定,即由结构基因组学向功能基因组学转变。研究获得不同处理下基因的差异表达谱是功能基因组学的重要一环,目前已经有多种检测基因差异表达的技术可供选用。在减法杂交技术和PCR基础上发展起来的DDRT—PCR、cDNA—RDA、cDNA—AFLP和SSH技术因其实用性而得到广泛的应用,并取得了令人满意的结果。     

Thermodynamic parameters based on a nearest-neighbor model for DNA sequences with a single-bulge loop

All 64 possible thermodynamic parameters for a single-bulge loop in the middle of a sequence were derived from optical melting studies. The relative stability of a single bulge depended on both the type of bulged base and its flanking base pairs. The contribution of the single bulge to helix stability ranged from 3.69 kcal/mol for a TAT bulge to -1.05 kcal/mol for an ACC bulge. Thermodynamics for 10 sequences with a GTG bulge were determined to test the applicability of the nearest-neighbor model to a single-bulge loop. Thermodynamic parameters for the GTG bulge and Watson-Crick base pairs predict, DeltaH degrees, DeltaS degrees, and T(M)(50 microM) values with average deviations of 3.0%, 4.3%, 4.7%, and 0.9 degrees C, respectively. The prediction accuracy was within the limits of what can be expected for a nearest-neighbor model. This certified that the thermodynamics for single-bulge loops can be estimated adequately using a nearest-neighbor model.