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排序方式: 共有432条查询结果,搜索用时 390 毫秒
171.
172.
Sandy Adriaenssens Jeroen Staelens Karen Wuyts Shari Van Wittenberghe Tatiana Wuytack Kris Verheyen Pascal Boeckx Roeland Samson 《Water, air, and soil pollution》2012,223(9):5643-5657
Tree canopies are believed to act as a sink of atmospheric ammonia (NH3). However, few studies have compared the uptake efficiency of different tree species. This study assessed the uptake of 15N-labelled NH3 at 5, 20, 50 and 100?ppbv by leaves and twigs of potted silver birch, European beech, pedunculate oak and Scots pine saplings in June, August and September 2008. Additionally, foliar uptake of 13C-labelled carbon dioxide (13CO2) and leaf stomatal characteristics were determined per species and treatment date and the relation with 15NH3 uptake and estimated stomatal 15NH3 uptake were assessed. Both 15NH3 and 13CO2 uptake were affected by tree species and treatment date, but only 15NH3 uptake was influenced by the applied NH3 concentration. Depending on the treatment date, 15NH3 uptake by leaves and twigs was highest at 5 (September), 20 (June) or 50 (August) ppbv. Birch, beech and oak leaves showed the highest uptake in August, while for pine needles this was in June and, except at 5?ppbv in June, the 15NH3 uptake was always higher for the deciduous species than for pine. For all species except beech 13CO2 uptake was highest in August and on every treatment date the 13CO2 uptake by leaves of deciduous species was significantly higher than by pine needles. Leaf characteristics and 13CO2 uptake did not provide a strong explanation for the observed differences in 15NH3 uptake. This study shows that on the short-term a high interspecific variability exists in NH3 uptake, which depends on the time in the growing season. 相似文献
173.
Getachew AM Innocent G Proudman CJ Trawford A Feseha G Reid SW Faith B Love S 《Veterinary research communications》2012,36(2):93-98
A 12/13 kDa antigen, tapeworm ELISA test, developed for use in horses, was used to detect parasite-specific serum antibody, IgG(T), in the serum of donkeys. In a pilot study the 12/13 kDa antigen was tested and proved to detect the antibody, IgG(T), in donkey sera. Blood samples from 797 donkeys, naturally exposed to cestode infection, from four geographical localities were collected and sera were prepared and analysed. There was substantial serological evidence that donkeys were potentially infected with A. perfoliata. A range of ELISA OD values were obtained from the serological assay. Over 26% and 7.5% of the donkeys were moderately and highly infected, respectively, showing at least a 34% sero-prevalence. The rest, 66.1%, were either with low infection intensity or negative for A. perfoliata infection. The risk of infections, both in sero-prevalence and intensity, as determined by ELISA optical density (OD), were highest in the highland areas of Ethiopia where pastures are low-lying and wet, and permanent pasture management is regularly practised. Sex, age and body condition of the donkeys had no significant effect either on prevalence of the infection or on the serum antibody level. These results indicate a risk of intestinal disorders, particularly, colic, associated with A. perfoliata infection in donkeys. 相似文献
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175.
Establishing trees in pastures can have production and conservation benefits, but is complicated by the presence of livestock.
The need to protect seedlings from livestock increases tree establishment costs, which in turn, can deter landowners from
planting trees. Living fences are a ubiquitous feature of pasture landscapes in the tropics that could help protect newly
planted trees by preventing livestock trampling and browsing. This study quantified the effectiveness of a living fence in
protecting tree seedlings during the first 2 years after planting. The four native tree species evaluated were: Cedrela odorata L., Pachira quinata (Jacq.) W.S. Alverson, Samanea saman (Jacq.) Merr., and Tabebuia rosea (Bertol.) A. DC. Results show that the living fence provided protection from livestock except in cases where tree species
were highly palatable as forage (i.e. P. quinata). Trees planted into the living fence generally had greater survival (62 vs. 28%), relative growth (10.3 times initial height
vs. 5.8 times initial height), and final height (191 cm vs. 108 cm) compared to those planted in open pasture after 2 years.
However, survival and growth of trees planted into the fence remained lower than that observed at a nearby plantation with
no livestock, regular weeding and no living fences. This study indicates that use of living fences as a protective barrier
could be an effective low-cost approach for establishing trees in tropical pasture landscapes.
相似文献
E. W. BorkEmail: |
176.
177.
T.L. Blanchard J.A. Thompson S.P. Brinsko D.D. Varner C.C. Love J. Ramsey A. O'Meara 《Journal of Equine Veterinary Science》2010
In Thoroughbred breeding, it is sometimes necessary to tranquilize a maiden mare to accomplish safe breeding by natural service. To determine whether tranquilization adversely affected fertility of maiden mares, pregnancy rates achieved in 792 matings of 531 maiden Thoroughbred mares were evaluated. One hundred sixty-three matings were accomplished after administration of a tranquilizer cocktail (20 mg acepromazine, 100 mg xylazine, and 10 mg butorphanol tartrate, injected intravenously), whereas 598 matings were accomplished without tranquilization. Pregnancy rate/cycle did not differ between maiden mares tranquilized before (64%; 105/163) and mares not tranquilized before mating (69%; 434/629) (χ2 = 1.048; P > .05). We concluded that tranquilization of maiden Thoroughbred mares immediately before mating did not adversely affect fertility. 相似文献
178.
179.
A simple approach to predicting dough sheeting thickness 总被引:1,自引:0,他引:1
Fuzhong Qi Shao-Cong Dai Marcus P. Newberry Richard J. Love Roger I. Tanner 《Journal of Cereal Science》2008,47(3):489-495
The prediction of final sheet thickness after rolling of wheat flour dough is studied using an approximate method that concentrates on the initial, intermediate and final material configurations. A newly proposed viscoelastic constitutive model containing a damage function is used. Compressibility and sideways spreading are ignored. Predictions of final sheet thickness given roll speed and diameter, gap and initial thickness data, show excellent agreement with available experiments on unyeasted dough, in contrast to many previous attempts. 相似文献
180.
Gérard Pergent Charles-François Boudouresque Olivier Dumay Christine Pergent-Martini Sandy Wyllie-Echeverria 《BMC ecology》2008,8(1):20