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991.
Why plants bother: root proliferation results in increased nitrogen capture from an organic patch when two grasses compete 总被引:30,自引:3,他引:27
We investigated whether the capacities of Lolium perenne L. and Poa pratensis L. roots to proliferate locally and to alter local nitrogen (N) inflows in a decomposing organic matter patch were important in their capture of N when grown together. In the presence of a patch, plants of both species were significantly heavier and contained more N. Root length and weight densities increased in the patch, but specific root length was unaltered. Although both species proliferated roots in the patch, L. perenne produced greater root length densities than P. pratensis , and also captured more N from the patch. Indeed, total N uptake from the patch was related to root length density within the patch. N inflows (rate of N uptake per unit root length) in the patch were no faster than in the whole root system for both species. Under the conditions of this study, root proliferation in an organic patch was more important for N capture from the patch than alterations in N inflows. Local proliferation of roots may be a key factor in interspecific competition for non-uniformly distributed supplies of N in natural habitats, so resolving the previous uncertainty as to the 'adaptive' nature of root proliferation. 相似文献
992.
目的对氩离子激光治疗口腔癌前病变的治疗机理、照射功率、方法及疗效差异进行探讨。方法 对53例口腔白斑和扁平苔藓患者应用Ar^+激光治疗,检查比较患者治疗前后的临床变化。结果 口腔白斑31例全部治愈,治愈率100%;口腔扁平苔藓22例治愈13例,显效7例,无效2例,治疗有效率90.9%,总有效率达96.2%。结论 氩离子激光治疗口腔白斑和扁平苔藓等清表的口腔慢性病损,不仅疗效显著,操作简便,并发症少 相似文献
993.
994.
995.
J M WHALEY D L SPARKES M J FOULKES J H SPINK T SEMERE R K SCOTT 《The Annals of applied biology》2000,137(2):165-177
The effects of reducing the plant density of winter wheat (cv. Haven) on canopy formation, radiation absorption and dry matter production and partitioning were investigated in field experiments in 1996/97 and 1997/98. Crop densities established ranged from 19 to 338 plants m?2. Grain yield was maintained with large reductions in plant density. At low plant densities the relative growth rate of the crop increased allowing a maintenance of crop dry matter production. An 18 fold reduction in plant density led only to a six fold reduction in green area index at the beginning of stem extension and by anthesis the difference was less than two fold. Crops grown at low plant densities increased green area per plant through increased duration of tiller production, green area per shoot and shoot survival. Main stem leaf number, phyllochron and tiller production rate were not significantly affected by plant density. Radiation use efficiency was greater at the low plant densities. We propose that better radiation distribution through the canopy and increased canopy nitrogen ratio were the causative mechanisms for this increase in RUE. As a result of increased green area per shoot and a decrease in ear production, more radiation was absorbed per shoot at the low plant densities, allowing an increase in grain number per ear from 32 to 48. 相似文献
996.
R. M. Olberg A. H. Worthington K. R. Venator 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2000,186(2):155-162
Perching dragonflies (Libellulidae; Odonata) are sit-and-wait predators, which take off and pursue small flying insects.
To investigate their prey pursuit strategy, we videotaped 36 prey-capture flights of male dragonflies, Erythemis simplicicollis and Leucorrhinia intacta, for frame-by-frame analysis. We found that dragonflies fly directly toward the point of prey interception by steering to
minimize the movement of the prey's image on the retina. This behavior could be guided by target-selective descending interneurons
which show directionally selective visual responses to small-object movement. We investigated how dragonflies discriminate
distance of potential prey. We found a peak in angular velocity of the prey shortly before take-off which might cue the dragonfly
to nearby flying targets. Parallax information from head movements was not required for successful prey pursuit.
Accepted: 11 November 1999 相似文献
997.
用Nd:YAG激光微束将处于丝分裂中期的小麦(Triticum aestivum L.)6B染色体微切割为四段,并用微细玻璃针将每个片段分别回收.将分离的染色体片段DNA用Sau3A接头介导的多聚酶链式反应(LA-PCR)分别扩增.Southem杂交证明4个特定区域的DNA确实来自于小麦基因组.用一系列(42对引物)位于6B染色体上的微卫星序列对微切割的染色体片段的PCR产物进行了验证.结果表明,获得的染色体片段的PCR产物来自于小麦6B染色体.将6B染色体4个片段的第二轮PCR产物克隆到pGET-vector中,建立了4个染色体特定区域的基因组文库,命名为R1、R2、R3和R4,分别包含2.1×105、2.74×105和2.93×105个重组子克隆.每个文库均随机挑选150个克隆进行质粒的小量制备和酶切验证.结果显示;插入片段大小在300~1800之间,平均大小为820~870bp,其中43%~48%的克隆为低/单拷贝序列,42%~47%为中/高拷贝序列.本研究为详细分析植物单染色体的不同片段的分子遗传学研究提供了基础. 相似文献
998.
Vitrification is the most sought after route to the cryopreservation of animal embryos and oocytes and other cells of medical, genetic, and agricultural importance. Current thinking is that successful vitrification requires that cells be suspended in and permeated by high concentrations of protective solutes and that they be cooled at very high rates to below −100 °C. We report here that neither of these beliefs holds for mouse oocytes. Rather, we find that if mouse oocytes are suspended in media that produce considerable osmotic dehydration before vitrification and are subsequently warmed at ultra high rates (10,000,000 °C/min) achieved by a laser pulse, nearly 100% will survive even when cooled rather slowly and when the concentration of solutes in the medium is only 1/3rd of standard. 相似文献
999.
1000.
ANNA PONJOAN GERARD BOTA ELADIO L. GARCÍA DE LA MORENA MANUEL B. MORALES AXEL WOLFF IGNASI MARCO SANTI MAÑOSA 《The Journal of wildlife management》2008,72(1):315-319
Abstract Capturing wild animals for research or conservation purposes may cause some adverse effects, which is only acceptable if these are outweighed by conservation benefits. We used information from 3 on-going telemetry studies on the endangered little bustard (Tetrax tetrax) in Western Europe to evaluate the risk factors associated with capture and handling. Of 151 telemetered birds, 23 (15.2%) exhibited impaired mobility and coordination after release, probably related to the occurrence of capture myopathy. Among the 23 impaired birds, 10 (43.5%) died before recovering normal mobility (6.6% of all birds captured). Logistic regression analyses identified longer handling time, longer restraint time, use of cannon nets, and capture of juveniles as inducing factors for these disorders. We conclude that little bustard is fairly susceptible to suffering ataxia and paresia after release as a result of restraint associated with capture and manipulation. Researchers can reduce this risk by keeping handling and restraint time below 10–20 minutes, particularly when using cannon nets or when capturing juveniles. 相似文献