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排序方式: 共有178条查询结果,搜索用时 703 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.
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
3.
Salma Kloula Ben Ghorbal Abdelwaheb Chatti Mohamed Marwan Sethom Lobna Maalej Mouadh Mihoub Sana Kefacha Moncef Feki Ahmed Landoulsi Abdennaceur Hassen 《Current microbiology》2013,67(1):112-117
The changes in lipid composition enable the micro-organisms to maintain membrane functions in the face of environmental fluctuations. The relationship between membrane fatty acid composition and UV-C stress was determined for mid-exponential phase and stationary phase Pseudomonas aeruginosa. The total lipids were obtained by dichloromethane/methanol (3:1) and were quantified by GC. The TLC analysis of phospholipids showed the presence of three major fractions phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin. Significant modifications, as manifested by an increase of UFA, were obtained. Interestingly, this microorganism showed a remarkable capacity for recovery from the stressful effects of UV-C. 相似文献
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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.
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
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8.
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:2,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
9.
Saoudi M Abdelmouleh A Kammoun W Ellouze F Jamoussi K El Feki A 《Comptes rendus biologies》2008,331(8):611-616
This study was undertaken to assess the risk of poisoning due to consumption of the puffer fish Lagocephalus lagocephalus collected along the Tunisian coast. Wistar rats were daily intraperitoneally injected, for 10 days, with acidic extracts of liver or flesh (muscles + skin) of L. lagocephalus. Control rats received injections of NaCl (0.9%). No mortality and no evident signs of neurotoxicity were recorded in treated rats. Conversely, treatment led to: (1) diarrhoea and body and organ (liver, kidney) weights loss; (2) oxidative stress evidenced by an increase in lipid peroxidation (TBARS) and conversely a decrease in antioxidant enzyme activities (SOD, catalase, GSH-Px) in tissues (blood cells, liver, kidneys); (3) a decrease in alanine aminotransferase (ALT) and alkaline phosphatase (ALP) activities in blood plasma. 相似文献
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