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101.
102.
C.M. Ghersa S.B. Perelman S.E. Burkart R.J.C. León 《Biodiversity and Conservation》2007,16(6):1575-1592
The Flooding Pampa natural grassland has an intricate pattern of plant communities, related to small topographic differences
that determine important changes in soil characteristics. Despite limitations imposed by soil properties and periodic waterlogging,
opportunistic tilling is carried out to plant pastures. There is little information on how pasture planting may affect the
structure of the grassland communities. In order to document changes caused by cultural activities on structural and functional
characteristics of plant communities in this landscape, we made field surveys in grasslands and very old pastures (grassland
communities recovered through secondary succession) using transects located across existing topographic gradients.
The patchy structure of this landscape was revealed by the multivariate analysis, by means of which four plant communities
could be identified in the natural grassland. Species composition of these communities differed from that of the corresponding
old pastures. They lost an important number of exclusive species, but also gained species: some new to the landscape and many
already present in other environments.
Pasture planting reduced the rate of species replacements along the gradient and produced changes in patchiness, but had no
effect on the species–area curve at the landscape scale. Neither did we find differences in total number of species, average
number of species/site and proportion of functional types. The new grassland created by opportunistic pasture planting has
developed into a structural gradient in which important differences occurred in the lower waterlogged-prone stands, whereas
the sites of the other communities experienced less structural changes. 相似文献
103.
Jutta Stadler Annette Trefflich Roland Brandl Stefan Klotz 《Biodiversity and Conservation》2007,16(3):621-630
Dry grasslands are among the most threatened plant communities of Central Europe. We explore the time scale of spontaneous
regeneration of dry grasslands on abandoned fields in an area of Central Europe, where also ancient grassland communities
occur (Saxony-Anhalt, Germany). On three permanent plots with shallow soils we monitored during 10 years change of species
composition and analysed whether spontaneous succession leads to assemblages similar to the ancient dry grassland communities
in the direct surroundings. We found that dry grassland species are able to invade the permanent plots and during the 10 years
of succession the number of dry grassland species increased. But even after 10 years there was a clear difference between
ancient dry grassland communities and the assemblages on the permanent plots. Our findings suggest two important conclusions:
First, spontaneous succession on abandoned fields is a cheap possibility for the conservation of some dry grassland species,
at least on shallow soils. Second, the time scale of the regeneration process, however, is rather long. Hence, conservation
of remnants of ancient grassland communities needs special attention. 相似文献
104.
Nurten Erdal Serkan Gürgül Ayla elik 《Mutation Research - Genetic Toxicology and Environmental Mutagenesis》2007,630(1-2):69-77
In this study, the genotoxic and cytotoxic potential of extremely low frequency magnetic fields (ELF-MF) was investigated in Wistar rat tibial bone marrow cells, using the chromosomal aberration (CA) and micronucleus (MN) test systems. In addition to these test systems, we also investigated the mitotic index (MI), and the ratio of polychromatic erythrocytes (PCEs) to normochromatic erythrocytes (NCEs). Wistar rats were exposed to acute (1 day for 4 h) and long-term (4 h/day for 45 days) to a horizontal 50 Hz, 1 mT uniform magnetic field generated by a Helmholtz coil system. Mitomycin C (MMC, 2 mg/kg BW) was used as positive control. Results obtained by chromosome analysis do not show any statistically significant differences between the negative control and both acute and long-term ELF-MF exposed samples. When comparing the group mean CA of long-term exposure with the negative control and acute exposure, the group mean of the long-term exposed group was higher, but this was not statistically significant. However, the mean micronucleus frequency of the longer-term exposed group was considerably higher than the negative control and acutely exposed groups. This difference was statistically significant (p < 0.01). The results of the MI in bone marrow showed that the averages of both A-MF and L-MF groups significantly decreased when compared to those in the negative control (p < 0.001 and p < 0.01, respectively). No significant differences were found between the group mean MI of A-MF exposure with L-MF. We found that the average of PCEs/NCEs ratios of A-MF exposed group was significantly lower than the negative control and L-MF exposed groups (p < 0.001 and p < 0.01, respectively). In addition, the group mean of the PCEs/NCEs ratios of L-MF was significantly lower than negative control (p < 0.01). We also found that the MMC treated group showed higher the number of CA and the frequency of MN formation when compared to those in all other each groups (p-values of all each groups <0.01) and also MMC treated group showed lower MI and the PCEs/NCEs ratios when compared to those in all other each groups (p-values of all groups <0.01). These observations indicate the in vivo suspectibility of mammals to the genotoxicity potential of ELF-MF. 相似文献
105.
The spatial and temporal variation of macroinvertebrate assemblages was studied in two Portuguese commercial rice agroecosystems
under the effect of field management involving the application of pesticides and fertilizers. A faunal succession of organisms
was observed on both fields. Grazers were the first to colonize the paddies after a dry period when pesticides were applied,
followed by development into nymphs and by an increase in the abundance of the species after the application of fertilizers.
At the end of the season when no pesticides or fertilizers were applied, the communities changed with the presence of adult
predators as a result of an increase in prey. Insecticide application revealed specific taxa increase due to the lack of competition
with the target organism. Macroinvertebrates tended to prefer infested field margins with aquatic, submerged vegetation, revealing
a spatial distribution along the paddies. Two different sampling devices were used and proved necessary in documenting the
macroinvertebrate communities (grab for benthic and hand-net for pelagic organisms). 相似文献
106.
107.
108.
Armin Kargol Leszek Malkinski Rahmatollah Eskandari Maya Carter Daniel Livingston 《Journal of biological physics》2015,41(4):421-431
We study the effect of micro-scale electric fields on voltage-gated ion channels in mammalian cell membranes. Such micro- and nano-scale electric fields mimic the effects of multiferroic nanoparticles that were recently proposed [1] as a novel way of controlling the function of voltage-sensing biomolecules such as ion channels. This article describes experimental procedures and initial results that reveal the effect of the electric field, in close proximity of cells, on the ion transport through voltage-gated ion channels. We present two configurations of the whole-cell patch-clamping apparatus that were used to detect the effect of external stimulation on ionic currents and discuss preliminary results that indicate modulation of the ionic currents consistent with the applied stimulus. 相似文献
109.
Jordi Toda Avelino Corma Raed H. Abudawoud Mohamed S. Elanany Ibrahim M. Al-Zahrani 《Molecular simulation》2015,41(16-17):1438-1448
A molecular dynamics study of diffusion of p-xylene and o-xylene has been performed over three different pure silica 10-ring zeolites, MFI, SFG and TUN. The shape selective properties of the frameworks of these three materials have been tested using four different types of force fields commonly used based on united atom, rigid-ion and core-shell approximations. The performance of each force field is analysed in order to find which force fields can give sufficiently accurate estimations that allow to select appropriate zeolites for selective separation of para/ortho xylene. This performance was found to depend on the quality of the structural properties of the zeolite, in particular the size and shape of the 10 rings which act as bottlenecks for the diffusion. The computational results allow us to define some optimum characteristics for the selective diffusion of p-xylene. 相似文献
110.
《RNA (New York, N.Y.)》2015,21(6):1066-1084
This paper is a report of a second round of RNA-Puzzles, a collective and blind experiment in three-dimensional (3D) RNA structure prediction. Three puzzles, Puzzles 5, 6, and 10, represented sequences of three large RNA structures with limited or no homology with previously solved RNA molecules. A lariat-capping ribozyme, as well as riboswitches complexed to adenosylcobalamin and tRNA, were predicted by seven groups using RNAComposer, ModeRNA/SimRNA, Vfold, Rosetta, DMD, MC-Fold, 3dRNA, and AMBER refinement. Some groups derived models using data from state-of-the-art chemical-mapping methods (SHAPE, DMS, CMCT, and mutate-and-map). The comparisons between the predictions and the three subsequently released crystallographic structures, solved at diffraction resolutions of 2.5–3.2 Å, were carried out automatically using various sets of quality indicators. The comparisons clearly demonstrate the state of present-day de novo prediction abilities as well as the limitations of these state-of-the-art methods. All of the best prediction models have similar topologies to the native structures, which suggests that computational methods for RNA structure prediction can already provide useful structural information for biological problems. However, the prediction accuracy for non-Watson–Crick interactions, key to proper folding of RNAs, is low and some predicted models had high Clash Scores. These two difficulties point to some of the continuing bottlenecks in RNA structure prediction. All submitted models are available for download at http://ahsoka.u-strasbg.fr/rnapuzzles/. 相似文献