北川不同海拔珙桐种群年龄结构研究

采用树木年代学的方法,按照珙桐的分布特点分海拔下限（1400 m～1500 m）,中部（1 600 m～1 700 m）,上限（1 800 m～1 900 m）,研究不同海拔梯度下北川珙桐种群的年龄结构,结果表明：海拔上限珙桐年龄结构偏大,缺乏幼苗及30 a～40a的个体;在海拔中部,30 a～40 a的个体占的比例较大,争夺空间和资源的能力更强;海拔下限的实生幼苗较多.在中部海拔分布的珙桐较多,且年龄结构集中在30 a～40 a之间,低海拔的种群特征是以幼苗为优势,而高海拔面有的幼苗却很少,表明海拔对珙桐种群年龄结构有重要的影响.     

Body shape variation in two species of darters (Etheostoma,Percidae) and its relation to the environment

Environmental variation can shape phenotypic variation in organisms, but most evidence for trait differentiation comes from analyses of dichotomous habitat types that differ in only one or few key environmental factors. In reality, environmental variation is often more subtle, gradual and multifarious. Here, we investigated geographic variation in body shape of two darter species (Etheostoma spectabile and Etheostoma flabellare; Percidae) that occur along river gradients. This study addressed three specific questions: Is there intraspecific geographic variation in the two species across different sites in the Ozark Highlands of Oklahoma (USA)? Is phenotypic variation across sites correlated with abiotic environmental conditions? Do the two species share site‐specific (i.e. convergent) phenotypic variation in areas where they occur together? Our results indicated significant body shape variation in both species. Population differences in body shape were particularly correlated with variation in substrate composition. The combined analysis of both species indicated a small but significant effect of convergence on body shape wherever they are sympatric; shared variation, however, was not related to any environmental variables included in the analysis. While it remains unclear whether phenotypic variation in these species is due to heritable differentiation or environmentally induced plasticity, our results indicate that even subtle and gradual environmental variation can induce substantial variation in phenotypes on a relatively small spatial scale.     

温度梯度对球面多点加压适张圆锯片固有频率的影响

该文通过对球面多点加压适张前后的圆锯片边缘加温,模拟实际使用时在锯片基体形成的温度场。分别对两种不同温度场下的未经适张圆锯片和经球面多点加压适张的圆锯片进行了振动模态测试。球面多点加压适张加压压力分别为22.5、34.5和45.6 kN。结果表明,未经适张处理圆锯片各阶固有频率在有温度场存在时下降很大,而经适张处理圆锯片的对应阶固有频率下降明显减少。而且随着温度场中由圆锯片边缘至中心的温度梯度增大,上述两者之间对应各阶固有频率变化的差异更加明显,当压点加压压力达到45.6 kN时,温度梯度对各阶固有频率影响呈减小趋势。      

Abiotic conditions and plant cover differentially affect microbial biomass and community composition on dune gradients

Dune systems are characterized by strong gradients of physical stress, with blowing sand and salt spray decreasing with distance from the ocean, and soil nutrients increasing. In this study we ask how soil microbial community composition and biomass change along transects away from the ocean, and whether these changes are regulated by abiotic stress or by resource availability. We collected bulk soil from under three plant species representative of the dune front, back, and flat: Ammophila breviligulata, Rosa rugosa, and Myrica pensylvanica. The biomass and composition of microbial communities were examined using phospholipid fatty acid (PLFA) analysis under patches of dominant vegetation, and in paired bare plots. We found that microbial biomass was strongly correlated with soil C, and thus the presence of vegetation. Community composition, on the other hand, varied with abiotic stresses, especially soil salinity. These variables in turn depended on distance from the shore, and were ameliorated in some cases by vegetation. These findings demonstrate that biomass and community composition are influenced by different environmental variables. Thus, relationships between biomass and composition are unlikely to be readily predicted on the basis of a single resource.     

Symmorphosis and livestock bioenergetics: production animal muscle has low mitochondrial volume fractions

A comparative analysis of skeletal muscle structure reveals that production species (nine species, representing three mammalian families and an avian family) have mitochondrial volume fractions (MVF) 37% lower than the non‐production species at equivalent size (17 species, with representatives from 10 mammalian families) ( Fig. 1 ; F_1,25 = 4.79; p = 0.039). As MVF provides evidence of oxidative capacity, this comparative analysis indicates that production animals share an exceptionally low oxidative capacity muscle phenotype. A possible bioenergetic reason for this observation, relating to a reduction in the cost of maintaining trans‐membrane ion gradients is briefly discussed. This discussion is framed within a biological economic design theory called symmorphosis and makes predictions about avenues for improvements in livestock bioenergetics.

Figure 1 Open in figure viewer PowerPoint The scaling of log skeletal muscle mitochondrial volume density (MVF) with log endotherm size. Production species (PS) (red circles, red line) have a 37% lower MVF than non‐production species (NPS) (blue circles, blue line). NPS log MVF = ?0.11 log M_b + 0.88 (r² = 0.48, n = 17). PS log MVF = ?0.11 log M_b + 0.74 (r² = 0.69, n = 9).     

连续T构箱梁桥竖向的升温模式

以黑龙江省三股线高架桥的实测温度数据为依据,对竖向温度梯度的变化规律进行了研究,得出了该桥的竖向升温模式;并对该升温模式、铁路桥规和公路桥规规定的竖向升温模式产生的温度自应力及外约束应力进行了计算与对比分析.结果表明,箱梁竖向最大升温温差发生在每天14时左右,1a中9月份的竖向升温温差相对较大;运用本地区竖向升温模式计算的混凝土拉应力略大于现行公路规范计算值,小于现行铁路规范计算值.     

干旱绿洲农田盐渍化对土壤理化特性和农艺特征的影响

在河西走廊西部大田试验条件下,通过一个生长季的观测,分析研究农田盐渍化对土壤理化特性和典型牧草(紫花苜蓿)和农作物(大麦)农艺性状、干物质积累和产量的影响。结果表明:(1)在0 ～ 20 cm土层,牧草土壤容重沿盐渍化梯度增加了3％,4.54％,8.62％,9.96％,农作物土壤容重没有明显变化规律;土壤有机质显著降低,且0～ 10 cm土层的降低速率快于10 ～ 20 cm土层;(2)盐渍化程度等于或高于中度盐渍化水平时,大麦植株的穗长、穗粒数和秸秆重受到显著影响;在开花、孕穗和灌浆期的盐度既会降低籽粒产量也降。低秸秆产量。与农作物相比,盐渍化程度等于或高于轻度盐渍化水平时,牧草植株的株高、主侧枝长和主根直径会受到影响,进而导致牧草产量的降低。因此,在农业生产中,可根据两种作物在不同盐渍化梯度各生育期的受害状况进行相应的水盐调控和耕作管理,以实现盐渍化农田作物产量的维持和增加。     

Total Carbon Storage in Himalaya Rangeland of Milke-Jaljale Area,Eastern Nepal

Rangelands occupy 51% of the terrestrial land surface, 23% total land of Nepal. It contains about 36% of the world＇s total carbon in above and belowground biomass. Rangelands can aid in the mitigation of rising atmospheric carbon dioxide concentrations via carbon storage in biomass and soil organic matter. A study on carbon stock on soil and vegetation at various altitudinal gradients in Milke-Jaljale rangeland area of Eastern Nepal was made. The study was carried out at three altitudinal gradients （above sea levels） Milke （3,000 m）, Gorujure （3,500 m） and Jaljale （4,000 m）. This method required establishing a transect line. Sample points were located by pacing the appropriate distances from the point of origin at a transect line. To determine distribution and quantity of plant carbon and soil organic carbon （SOC）, 45 sample points were established and 15 points were sampled from each study site. Total soil carbon was estimated as follows： 17.65 t/ha at Milke, 17.27 t/ha at Gorujure and 28.33 t/ha at Jaljale. Similarly, total vegetation carbon was estimated 22.68 t/ha at Milke, 29.79 t/ha at Gorujure and 42.54 t/ha at Jaljale. Highest elevation study site with least external disturbance （Jaljale area） had high storage of carbon in both cases vegetation and soil.     

西藏色季拉山土壤微生物量碳和易氧化态碳沿海拔梯度的变化

为探讨不同海拔梯度对土壤活性有机碳库的影响,以西藏色季拉山(西坡)的高山灌丛(AS)、杜鹃林(RF)、急尖长苞冷杉林(AGSF1～6)和林芝云杉林(PLLF)为试验对象,研究林地土壤有机碳、微生物量碳和易氧化态碳的变化特征。结果表明:高海拔植被类型具有较高的土壤活性有机碳含量和分配比例。土壤有机碳含量与土壤pH值和容重呈显著负相关(p<0.05)。在土壤剖面垂直分布上,随着土壤深度增加,土壤总有机碳、微生物量碳和易氧化态碳含量均呈现随土层深度增加而逐渐减小的变化规律。土壤总有机碳、微生物量碳和易氧化态碳含量沿海拔梯度具有明显的变化规律,即随海拔的升高,土壤总有机碳、微生物量碳和易氧化态碳含量逐渐变大。土壤微生物量碳和总有机碳量有较好的正相关性,有机碳含量越高,土壤微生物量碳越大。     

Why Are Mares with Pneumovagina Susceptible to Bacterial Endometritis? A Personal Opinion

Pneumovagina is the abnormal presence of air in the vagina, which may lead to pneumometra and endometritis. Predisposing factors are abnormal perineal conformation and weakness of the vestibulovaginal sphincter. This report examines why ponies and some other breeds are less susceptible to pneumovagina than Thoroughbreds and consequently less susceptible to endometritis. Observations on vaginal ballooning during vaginoscopic examination led to the conclusion that there is a fundamental difference in intra-abdominal pressures between horses and ponies, and between mares with high or low body condition scores. This difference in the extreme cases, for example, a small fat pony versus a large thin Thoroughbred, means that the pressure gradient in the former is from the uterus through the vagina to the exterior, whereas the case is reversed in the latter. Although the uterus is at a negative pressure relative to the exterior, evacuation of fluids is seriously disadvantaged, leading to an inability to resolve uterine infections.