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Selected AbstractsVariability of total and solid precipitation in the Canadian Arctic from 1950 to 1995INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 4 2002Rajmund Przybylak Abstract Trends in solid and total precipitation, as well as in the ratio of solid to total precipitation (hereinafter S/T ratio), in the Canadian Arctic in recent decades have been investigated. In addition, the influence of air temperature and circulation factors (atmospheric and oceanic) on the above-mentioned precipitation characteristics have been examined. Recently updated and adjusted data by the Canadian Climate Centre from 16 stations located in the Canadian Arctic and two stations from the sub-Arctic were used for the investigation. The southern boundary of the study area was taken after Atlas Arktiki (Tresjinkov, A. 1985. Glavnoye Upravlenye Geodeziy i Kartografiy: Moscow; 204 pp). The majority of the data cover the period from 1950 to 1995. A statistically significant increase in all kinds of areally averaged seasonal and annual precipitation for the Canadian Arctic over the period 1950,95 has been found. On the other hand, the S/T ratio did not change significantly, except for summer values, and its behaviour was also in accord with small variations noted in air temperature. An increase in air temperature in the Canadian Arctic most often led to a rise in all kinds of annual precipitation sums, but only when the warmest and coldest years were chosen based on individual stations. The pattern of the relationship is significantly more complicated, and can even be opposite to that presented above, when the sets of the warmest and coldest years are chosen based on the areally averaged annual temperature for the Canadian Arctic. Significantly more stable results of changes were found for the S/T ratio, which in warmer periods was usually lower. However, more detailed and reliable investigations of temperature,precipitation relationships conducted for individual stations showed that though the S/T ratio in warmer periods may well be lower, this only applies to the southern (warmer) part of the Canadian Arctic (<70 °N). During periods with high positive values of the North Atlantic Oscillation Index (NAOI), a decrease in precipitation is observed in the south-eastern part of the Canadian Arctic, i.e. in the area where strong cooling was also observed. During El Niño events most of the Canadian Arctic had both greater precipitation and a higher S/T ratio than during La Niña events. The most unequivocal results of precipitation and S/T ratio changes were found for changes in the Arctic Ocean circulation regimes. In almost the whole study area, a lower precipitation and S/T ratio were noted during the anticyclonic circulation regime in the Arctic Ocean. Copyright © 2002 Royal Meteorological Society [source] Consequences of a decentralized participatory barley breeding programme on changes in SSR allele frequency and diversity in one cycle of selectionPLANT BREEDING, Issue 5 2007F. Fufa Abstract Changes in allele type, allele frequency and genetic diversity because of selection by individual farmers and breeders were assessed using simple sequence repeats (SSRs) during one cycle of selection in a decentralized participatory barley breeding programme. Selection by both breeders and farmers resulted in the loss of a number of alleles in the majority of the locations, with more alleles lost in the heterogeneous breeding materials than in the fixed genotypes, indicating selection against undesirable traits uncovered in the heterogeneous breeding materials that are presumably linked to SSR alleles. After selection, significant allelic frequency changes were observed at several loci in both the germplasm groups. As the selection was conducted independently in each location, an allele had a chance of being selected in more than one location, and therefore considering the whole study area the allelic composition and diversity of the original genetic materials was maintained after the selection. The study showed the importance of decentralized participatory plant breeding in maintaining genetic diversity that helps stabilize and sustain production in unpredictable production conditions. [source] Life on the edge , to which degree does phreatic water sustain vegetation in the periphery of the Taklamakan Desert?APPLIED VEGETATION SCIENCE, Issue 1 2010Helge Bruelheide Abstract Questions: Do the vegetation-specific patterns in the forelands of river oases of the Taklamakan Desert provide clues to the degree to which a vegetation type depends on unsaturated soil moisture, brought about by extensive floodings, or phreatic water? Location: Foreland of the Qira oasis on the southern rim of the Taklamakan Desert, Xinjiang Uygur Autonomous Region, China. Methods: A vegetation map was prepared using a SPOT satellite image and ground truthing. Measurements of soil water contents were obtained from a flooding experiment and transformed into water potentials. Sum excedance values were calculated as the percentage of days on which different thresholds of soil water potentials were transgressed. Groundwater depth was mapped by drilling 30 groundwater holes and extrapolating the distances to the whole study area. Results: The vegetation was characterized by only six dominant or codominant species: Alhagi sparsifolia, Karelinia caspia, Populus euphratica, Tamarix ramosissima, Calligonum caput-medusae and Phragmites australis. The vegetation patterns encountered lacked any linear features typical of phreatophytes, thus not allowing direct conclusions on the type of the sustaining water sources. Soil water potentials never transgressed a threshold of pF 5 (,10 MPa) in horizons above the capillary fringe during periods without inundation, thus representing water not accessible for plants. Depth to the groundwater ranged between 2.3 and 17.5 m among plots and varied between 1.7 and 8.0 m within a plot owing to dune relief. The seven main vegetation types showed distinct niches of groundwater depths, corresponding to the observed concentric arrangement of vegetation types around the oasis. Conclusions: Inundation by flooding and unsaturated soil moisture are irrelevant for the foreland vegetation water supply. Although distances to the groundwater table can reach about 20 m, which is exceptionally large for phreatophytes, groundwater is the only water source for all vegetation types in the oasis foreland. In consequence, successful maintenance of oasis foreland vegetation will crucially depend on providing non-declining ground water tables. [source] Low population differentiation and high genetic diversity in the invasive species Carduus acanthoides L. (Asteraceae) within its native range in the Czech RepublicBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2009BOHUMIL MANDÁK Colonizing species are predicted to suffer from reductions in genetic diversity during founding events. Although there is no unique mode of reproduction that is characteristic of successful plant colonizers, many of them are predominantly self-fertilizing or apomictic species, and almost all outcrossing colonizers are self-compatible. Carduus acanthoides comprises a species of disturbed habitats with wind-dispersed seeds that colonizes open spaces of various sizes. Population genetic diversity was expressed by assessing patterns of variation at nine putatively neutral allozyme loci within and among 20 natural populations in its native distribution range in the Czech Republic. Overall, C. acanthoides displayed high levels of genetic diversity compared to other herbaceous plants. The percentage of polymorphic loci was 84.5, with values of 2.37, 0.330, and 0.364 for the mean number of alleles per polymorphic locus (A), observed heterozygosity (Ho), and expected heterozygosity (He), respectively. There was only weak evidence of inbreeding within populations (f = 0.097) and very low genetic differentiation among populations (, = 0.085). Analyses of the data provide strong evidence for isolation-by-distance for the whole study area. Even the colonizing species, C. acanthoides, currently supports a substantial amount of allozyme variation at both the species and population levels. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 596,607. [source] | |||||||||||||