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排序方式: 共有115条查询结果,搜索用时 15 毫秒
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Experimental evidence shows that site fertility is a key modulator underlying plant community changes under climate change. Communities on fertile sites, with species having fast dynamics, have been found to react more strongly to climate change than communities on infertile sites with slow dynamics. However, it is still unclear whether this generally applies to high‐latitude plant communities in natural environments at broad spatial scales. We tested a hypothesis that vegetation of fertile sites experiences greater changes over several decades and thus would be more responsive under contemporary climate change compared to infertile sites that are expected to show more resistance. We resurveyed understorey communities (vascular plants, bryophytes, and lichens) of four infertile and four fertile forest sites along a latitudinal bioclimatic gradient. Sites had remained outside direct human disturbance. We analyzed the magnitude of temporal community turnover, changes in the abundances of plant morphological groups and strategy classes, and changes in species diversity. In agreement with our hypothesis, temporal turnover of communities was consistently greater on fertile sites compared to infertile sites. However, our results suggest that the larger turnover of fertile communities is not primarily related to the direct effects of climatic warming. Furthermore, community changes in both fertile and infertile sites showed remarkable variation in terms of shares of plant functional groups and strategy classes and measures of species diversity. This further emphasizes the essential role of baseline environmental conditions and nonclimatic drivers underlying vegetation changes. Our results show that site fertility is a key determinant of the overall rate of high‐latitude vegetation changes but the composition of plant communities in different ecological contexts is variously impacted by nonclimatic drivers over time. 相似文献
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Koivula T Ekman M Leitner T Löfdahl S Ghebremicahel S Mostowy S Behr MA Svenson SB Källenius G 《Microbes and infection / Institut Pasteur》2004,6(3):272-278
In a previous study of Mycobacterium tuberculosis complex isolates from Guinea-Bissau in West Africa, we identified a unique group of strains, designated here as the Guinea-Bissau family of strains, which, although genotypically closely related, phenotypically demonstrated a considerable heterogeneity. We conducted here a detailed genotypic analysis of a subset (n = 35) of these isolates. Based on the data obtained, and by comparison of known corresponding genes in mycobacteria outside the M. tuberculosis complex, we propose that the Guinea-Bissau strains belong to a unique branch of the M. tuberculosis complex tree in between classical M. tuberculosis and classical M. bovis. These observations are discussed in their significance in M. tuberculosis complex classification. 相似文献
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Liukkonen-Anttila T Honkanen H Peltokangas P Pelkonen O Hohtola E 《Comparative biochemistry and physiology. Toxicology & pharmacology : CBP》2003,134(1):69-77
We examined hepatic cytochrome P450 activity in wild and hand-reared grey partridges (Perdix perdix), capercaillies (Tetrao urogallus) and ring-necked pheasants (Phasianus colchicus), as well as the enzyme activity in a variety of tissues of hand-reared Japanese quails (Coturnix coturnix japonica) and pigeons (Columba livia). Post-mortem decrease in hepatic enzyme activity in the grey partridge was measured. Hepatic 7-ethoxyresorufin-O-deethylase activity was similar in wild and hand-reared grey partridges and pheasants, but the activity was significantly lower in wild than in hand-reared capercaillies, probably resulting from their phenolic-rich diet. In the tissues of both quails and pigeons 7-ethoxycoumarin-O-deethylase exhibited the highest and 7-pentoxyresorufin-O-deethylase the lowest activity. Hepatic enzyme activity was significantly higher than that in other tissues. In the small intestine some activity could be found, reflecting some intestinal detoxication capacity. Enzyme activity decreased by 34-69% during the 30-min sampling period, which confirmed the importance of equalising sampling time to obtain comparable data. Because the hand-reared birds in this study were fed the same commercial diets, we assumed that the enzyme activity values detected reflect species differences without any induction by dietary secondary compounds. 相似文献
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The crystals of the soil-isolated Bacillus thuringiensis (Bt) strain A4 consist of two polypeptides with molecular mass of 140 kDa and 32 kDa that exhibit insecticidal activity against
adult flies of Bactrocera oleae (Diptera). Plasmid curing applied to this strain resulted in the isolation of several subclones exhibiting alterations in
their crystal polypeptides as well as two acrystalliferous subclones. The crystals of subclone 1.1 lacked the 32-kDa polypeptide
and consisted uniquely of a 140-kDa polypeptide antigenically related to the parental 140-kDa crystal polypeptide. Additionally,
the crystals of this subclone exhibited insecticidal activity against B. oleae equivalent to that of the parental strain. Therefore, the 32-kDa crystal polypeptide is dispensable for insecticidal activity,
which appears to be dependent on the presence of the 140-kDa crystal polypeptide.
Received: 5 April 2000 / Accepted 2 May 2000 相似文献
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Navrozidis EI Vasara E Karamanlidou G Salpiggidis GK Koliais SI 《Journal of economic entomology》2000,93(6):1657-1661
Bacillus thuringiensis, isolate 114A, was used in toxicity experiments against the wild population ofthe olive pest Bactroceria oleae (Gmelin). In laboratory experiments, spores and crystals of the B.t. were delivered to the insects with the food. Longevity, oviposition period, number of eggs produced, and percent hatch were recorded. Olive fruits from the oviposition test were dipped into a suspension containing spores and crystals of B. thuringiensis 114A after the eggs were deposited. In field experiments, four to six sprayings per year of B.t. 114A isolate were applied for three successive years. It was found that, in addition to the longevity of B. oleae, the oviposition period, number of eggs and percent egg hatch decreased. Also, the percentage of pupation and emergence was reduced when olive fruits with eggs in their mesocarp were dipped in the solution of spores and crystals. Field applications with the toxins of 114A isolate of B. thuringiensis have resulted in significant protection of the olive production. 相似文献
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Cryopreservation of embryogenic cultures of Scots pine 总被引:7,自引:2,他引:5
Häggman Hely M. Ryynänen Leena A. Aronen Tuija S. Krajnakova Jana 《Plant Cell, Tissue and Organ Culture》1998,54(1):45-53
The aim of the study was to develop an effective cryopreservation method for Scots pine (Pinus sylvestris L.) embryogenic
cultures. Altogether nine cell lines derived from three mother trees were cryopreserved after cold hardening using dimethylsulfoxide
or two different mixtures of polyethyleneglycol 6000, glucose and dimethylsulfoxide as cryoprotectants. Seventy-eight percent
of the cell lines remained viable after cryostorage, the best cryoprotectant treatment being 10% polyethyleneglycol 6000,
10% glucose, and 10% dimethylsulfoxide in water. This treatment resulted in significantly better regrowth of the embryogenic
cultures than with the other cryoprotectants or with the controls. According to microscopical observations, the cells that
retained their viability and regrowth ability after cryopreservation were the embryonal head cells, as well as some elliptic
suspensor cells close to the embryonal head cell area. When proliferation growth of the frozen cultures had started, their
morphological appearance was the same as the non-frozen cultures. In addition, the RAPD assays suggested that the cryostorage
treatment used here preserved the genetic fidelity of the Scots pine embryogenic cultures.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
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Jukka Bisi Tuija Liukkonen Sakari Mykrä Mari Pohja-Mykrä Sami Kurki 《European Journal of Wildlife Research》2010,56(5):771-779
This article focuses on the roots of the Finnish wolf conflict by using stakeholder evaluations of the wolf as a tool. The
recent growth of the wolf population has highlighted stakeholders’ contradictory objectives and revealed a conflict between
the two main stakeholders, conservationists and hunters, in wolf management. The question of hunting emerges as the core of
the conflict. The negative evaluation of the wolf by hunters reflects a competitive situation, which is typical of the historical
development of wolf management in Finland. In areas with the most abundant wolf populations, hunters view the wolf most negatively.
This study clearly demonstrates that the Finnish wolf conflict is rooted in the values of modern society and carries a long
historical, practical and ecological background in which humans and wolves compete over resources, mainly the moose. The conflict
between hunters and conservationists in wolf management is connected to the appreciation of moose as game and stems from competition
between humans and wolves over their prey and the historical presence or absence of the wolf. 相似文献