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排序方式: 共有191条查询结果,搜索用时 15 毫秒
1.
Effects of a forest disturbance on shredder production in southern Appalachian headwater streams 总被引:2,自引:0,他引:2
- 1 The effects of a forest disturbance were investigated by comparing production of leaf-shredding aquatic insects in three streams draining a mature hardwood forest and three streams draining an 11-year-old, cable-logged clearcut.
- 2 Reference streams contained significantly greater mean annual standing crop of leaf material and significantly more slow-processing leaf material than disturbed streams. Disturbed streams had a significantly higher mean annual standing crop of fast-processing leaf material than the reference streams.
- 3 Leaf-shredding cranefly (Tipula abdominalis), caddisfly (Pycnopsyche gentilis), and stonefly (Tallaperla maria) larvae comprised over 95% of shredder biomass in all streams. Total shredder production was significantly greater (P<0.05) in disturbed versus reference streams, but individual production rates were not significantly different between stream types.
- 4 Pycnopsyche gentilis larvae were present at higher densities and achieved significantly greater annual biomass in disturbed versus references streams, Biomass of P. gentilis was significantly correlated with the standing crop of fast-processing, early successional leaf material in samples, whereas biomass of other shredders was correlated significantly with medium or slow-processing leaf species characteristic of later stages of forest succession.
2.
Evidence for a Protein Gel Structure Cross-linked by Metal Cations in the Intercellular Cement of Plant Tissue 总被引:1,自引:0,他引:1
The factors which modify the action of chelating agents in dissolvingthe intercellular cement in plant tissue have been investigated.The action was assessed by determining the degree of separationof cells in treated pea root tips. Greatly increased separation was observed when heavy metal chelatingagents were combined with EDTA (which, in addition to heavymetals, chelates Ca) indicating that two types of cations areinvolved in stabilizing the cement. After the cells had beenseparated by removal of the cations they could be recementedby treatment with divalent cations. In low concentrations onlycertain combinations of cations were effective, again pointingto the presence of more than one type of cation in the cement.Proteolytic enzymes or denaturing agents eliminated this capacityto recement. Pretreatment with divalent cations enhanced subsequentseparation (in EDTA solution). This effect could be counteredby treatment with monovalent cations. Pretreatment in buffers covering a wide range of pH resultedin increased separation both at pH 3 and at pH 11, suggestingan ampholytic component in the cement. Urea, when applied as a pretreatment, only enhanced separationwhen in high concentration. This effect was influenced by ionicstrength. When applied in combination with EDTA, urea producedan optimum effect at low concentration (0.125 M.). Pretreatmentin hot water also enhanced subsequent separation in EDTA solutions.High concentrations of KCl countered this effect. These findingspoint to the importance of H bonds in the intercellular cement.Thioglycollic acid, applied either as pretreatment or simultaneouslywith EDTA, lowered the EDTA concentration necessary to achieveseparation, suggesting the presence of SS bridges. The curve relating the effect of pretreatment at varying temperatures,either in H2O or in apolar solvents, to temperature, showeda sharp break, suggesting that the melting-point of an organizedgel might be involved. The conclusion is reached that the intercellular cement canbe regarded as an oriented gel structure containing proteinmolecules cross-linked by two types of metallic ion, the metalliccross linkage being chelate in character. 相似文献
3.
AdTGF-β1223/225气管内注射制备大鼠肺间质纤维化动物模型 总被引:1,自引:1,他引:1
目的观察TGF-β1基因过表达诱发大鼠肺间质纤维化动物模型的组织病理学变化.方法成年健康SD大鼠30只,随机分为空白对照组10只,模型组10只和空载体对照组10只,其中对模型组大鼠气管内一次性注射携带TGF-β1基因腺病毒载体(AdTGF-β1 223/225,1×109 pfu,0.4 mL),空白对照组大鼠气管内注射等量的生理盐水,空载体对照组大鼠气管内注射等量的腺病毒空载体.结果一次性肺气管内注射 AdTGF-β1 223/225可造成肺急性炎症和肺间质纤维化,而对照(腺病毒空载体)并不引起相应的变化.结论肺组织局部分泌的细胞因子TGF-β1可以单独诱发肺间质纤维化. 相似文献
4.
ROBERT G. DOUPÉ MATTHEW J. KNOTT JASON SCHAFFER DAMIEN W. BURROWS ALAN J. LYMBERY 《Austral ecology》2010,35(1):24-30
This study describes experimental herbivory and detritivory of three common native aquatic macrophyte species by the introduced Mozambique tilapia Oreochromis mossambicus (Peters) (Pisces: Cichlidae), and its physiological response to their consumption. There was a highly significant effect of fish herbivory on plant weight for each of the macrophyte species, but this effect was not influenced by any preference for periphyton. Despite the herbivory, there was a highly significant loss of fish body weight across all plant species and weight could only be maintained by supplementary feeding of a high protein fish flake. These results suggest that despite eating these plants, an alternative food resource may be needed for survival and may trigger trophic plasticity in O. mossambicus. 相似文献
5.
The invasion of woody plants into grass‐dominated ecosystems has occurred worldwide during the past century with potentially significant impacts on soil organic carbon (SOC) storage, ecosystem carbon sequestration and global climate warming. To date, most studies of tree and shrub encroachment impacts on SOC have been conducted at small scales and results are equivocal. To quantify the effects of woody plant proliferation on SOC at broad spatial scales and to potentially resolve inconsistencies reported from studies conducted at fine spatial scales, information regarding spatial variability and uncertainty of SOC is essential. We used sequential indicator simulation (SIS) to quantify spatial uncertainty of SOC in a grassland undergoing shrub encroachment in the Southern Great Plains, USA. Results showed that both SOC pool size and its spatial uncertainty increased with the development of woody communities in grasslands. Higher uncertainty of SOC in new shrub‐dominated communities may be the result of their relatively recent development, their more complex above‐ and belowground architecture, stronger within‐community gradients, and a greater degree of faunal disturbance. Simulations of alternative sampling designs demonstrated the effects of spatial uncertainty on the accuracy of SOC estimates and enabled us to evaluate the efficiency of sampling strategies aimed at quantifying landscape‐scale SOC pools. An approach combining stratified random sampling with unequal point densities and transect sampling of landscape elements exhibiting strong internal gradients yielded the best estimates. Complete random sampling was less effective and required much higher sampling densities. Results provide novel insights into spatial uncertainty of SOC and its effects on estimates of carbon sequestration in terrestrial ecosystem and suggest effective protocol for the estimating of soil attributes in landscapes with complex vegetation patterns. 相似文献
6.
Genotype and phenotype associations with drought tolerance in barley tested in North Africa 总被引:8,自引:0,他引:8
B P FORSTER R P ELLIS J MOIR V TALAMÈ M C SANGUINETI R TUBEROSA D THIS B TEULAT-MERAH I AHMED S A E E MARIY H BAHRI M EL OUAHABI N ZOUMAROU-WALLIS M EL-FELLAH M BEN SALEM 《The Annals of applied biology》2004,144(2):157-168
A review is presented of genetic strategies deployed in a 3-yr project on drought tolerance in barley. Data were collected on genetic, physiological and agronomic traits in non-irrigated and irrigated field trials in Egypt, Morocco and Tunisia. A wide range of barley germplasm (developed from African and European cultivars, adapted landraces and wild barleys) was tested, and positive traits were found in each gene pool. The contrasting environments of the three North African countries had major effects on plant/genotype performance. Genetic effects were also detected, as were genotype × environment interactions. A range of strategies were deployed to investigate the physiology and genetics of quantitative traits associated with field performance. Quantitative trait locus (QTL) analysis was performed using backcross lines, recombinant inbred lines and doubled haploid mapping populations. A detailed genetic map was generated in the Tadmor × (ER/Apm) recombinant inbred lines, an important mapping population specifically developed by ICARDA (Centre for Agricultural Research in Dry Areas) and CIMMYT (International Maize and Wheat Improvement Center) to study drought. Quantitative trait loci (QTLs) for grain yield and other important morphological and physiological traits were also identified in a population of doubled haploids derived from F2BCj plants from a cross between a cultivar and a wild barley accession. Significantly, the wild parental line was found to contribute a number of positive alleles for yield. Effects of major developmental genes could explain many of the responses observed. QTLs were found to cluster around major genes controlling flowering time (sghI), plant stature (sdwI and arie.GP) and ear type (vrsl), and it is highly likely that the associations represent pleiotropic effects. Some QTLs were associated with candidate genes such as dehydrins and rubisco activase. One of the most significant results was the identification and generation of material that out performed the best local standards in the three participating North African countries; the selected lines have now entered local breeding programmes. The strategies adopted provided information on physiological traits, genotypes and genetic markers that could be used for marker-assisted selection. Target QTLs and their associated genetic markers may be deployed in marker assisted selection programmes to match crop phenology to the field environment. 相似文献
7.
四步法消除SYBR GreenⅠ实时定量RT-PCR中引物二聚体的影响 总被引:18,自引:0,他引:18
为建立一种新的SYBRgreenⅠ实时定量RT PCR方法 ,使之能够有效消除引物二聚体 (PDs)对实时定量结果的影响 .对RT PCR特异性扩增产物和PDs分别进行了凝胶电泳检测和熔解曲线分析 .依据PDs和扩增产物的熔解温度 (Tm)特点 ,在通用的三步法的延伸步骤之后 ,增加一个短暂的 (5s)恒温和荧光检测步骤 ,使这个步骤的温度高于PDs的Tm,但低于扩增产物的Tm,简称该法为四步法 .PDs的Tm 通常高于 72℃ ,但低于扩增产物的Tm .将四步法第四步的温度设置在高于PDs的Tm ,但低于扩增产物的Tm 时 ,四步法能够有效地消除PDs的影响 .对三步法和四步法SYBRgreenⅠ实时定量RT PCR进行了比较 ,发现三步法根本不能用于RNA的实时定量 ,而四步法能够实现包括低丰度RNA在内的RNA的定量 .选择Tm 值尽可能小的引物 ,使PDs与扩增产物Tm 值之间有足够的差距 ,将更有利于四步法的应用 ,并可成功地用于低丰度RNA的准确定量 相似文献
8.
Effects of fire on regional evapotranspiration in the central Canadian boreal forest 总被引:2,自引:0,他引:2
BEN BOND-LAMBERTY SCOTT D. PECKHAM† STITH T. GOWER† BRENT E. EWERS‡ 《Global Change Biology》2009,15(5):1242-1254
Changes in fire regimes are driving the carbon balance of much of the North American boreal forest, but few studies have examined fire‐driven changes in evapotranspiration (ET) at a regional scale. This study used a version of the Biome‐BGC process model with dynamic and competing vegetation types, and explicit spatial representation of a large (106 km2) region, to simulate the effects of wildfire on ET and its components from 1948 to 2005 by comparing the fire dynamics of the 1948–1967 period with those of 1968–2005. Simulated ET averaged, over the entire temporal and spatial modeling domain, 323 mm yr−1; simulation results indicated that changes in fire in recent decades decreased regional ET by 1.4% over the entire simulation, and by 3.9% in the last 10 years (1996–2005). Conifers dominated the transpiration (EC) flux (120 mm yr−1) but decreased by 18% relative to deciduous broadleaf trees in the last part of the 20th century, when increased fire resulted in increased soil evaporation, lower canopy evaporation, lower EC, and a younger and more deciduous forest. Well‐ and poorly drained areas had similar rates of evaporation from the canopy and soil, but EC was twice as high in the well‐drained areas. Mosses comprised a significant part of the evaporative flux to the atmosphere (22 mm yr−1). Modeled annual ET was correlated with net primary production, but not with temperature or precipitation; ET and its components were consistent with previous field and modeling studies. Wildfire is driving significant changes in hydrological processes by affecting mean stand age, forest species, and energy balance. These changes, particularly in poorly drained areas, may control the future carbon balance of the boreal forest. 相似文献
9.
10.
The meridian phenomena are closely associated with the neuro-muscular function. Our experiments show that meridian phenomenon, acupoint stimulation-induced generating-sensations along meridians (GSM), does exist in some volunteers, and the subjects can describe the characteristics of the feelings and the route of GSM. Simultaneously, GSM is often accompanied with progressive myoelectric activity along the meridian which is able to be recorded objectively. Bra-chial plexus anesthesia and regional neuro-muscular block may arrest these responses while the neuro-muscular blocking agent may stop neuromuscular transmission at the motor end-plate rather than check GSM. The facts reveal that GSM probably depends on muscular activity and is involved in the secondary neuro-muscular excitation propagating along the longitudinal axis of muscles. These findings suggest that the myoelectric activities constitute the foundation of secondarily generating-sensation propagating along the longitudinal orientation of limbs 相似文献