Aral Sea - Where the fourth largest lake in the world had gone? During the last 50 years the single water body of Aral Sea was subdivided into several small lakes. Lake level was lowered by more than 25 m, its area was reduced dramatically. Lake desiccation is accompanied by changes in chemical (water) mineralization, physical (hydrodynamics), and also biological lake characteristics. The major cause of described changes is long-term overusing of the water of both tributaries for irrigaton purposes.
Aral Sea - Socio-economic problems of Aral Sea Region (How ended commanding to a wind and rain). Ones the world´s fourth largest lake was meant to be sacrified in the name of former Soviet economy. Area of most of the Central Asia is depended on agriculture, which is depended on massive irrigation from the main tributaries of Aral Sea. Water hence became after 1991 the source of political conflicts between water rich and energy poor upstream countries and water poor and natural resources rich downstream countries.
Aral Sea - All appearances of Aral Sea lake. The lake level fall of Aral Sea during the last fifty years was not the only dramatic low-stand in its history. In last two thousand years four major regressions have been recognized. During one of these regressions (at -0-400 AD) lake level was probably lower than in the last decade. This knowledge has opened the theme of the rate of anthropogenic and natural influences to the lake level fall. Despite that people has influenced the area for several thousand years the leading factor causing Aral Sea desiccation was probably climate. People has "only" reacted to the climatic worsening and caused acceleration of the natural processes.
1_Chestnut (Castanea sativa Mill.) is one of the economically more important trees in the north of Portugal. Spiders, as generalist predators, are potential controlling agents of pests, yet the composition of the community of spiders associated with this crop is only poorly known. The objective of this study was to determine the spider communities in the canopies of chestnut trees subject to three different soil management practices in northeastern Portugal. Three chestnut groves each subject to a different agricultural practice (grazed, tilled or untilled) were studied in 2008 and 2009. The Araneae communities were sampled by beating the branches and the individuals collected were identified to family and species when possible. To investigate the structure of the spider community in each grove the abundance and family richness of spiders were calculated and compared between managements. In total, 4172 spiders were collected and, in both years, the three most abundant families were Araneidae, Philodromidae and Linyphiidae. In 2008, there was a greater abundance of spiders in the grazed, followed by the tilled and untilled groves, but no significant differences among groves. However, in 2009 there was a greater abundance of spiders in the tilled grove, followed by grazed and untilled groves and the differences between the untilled and the other two groves were significant. Araniella, Oxyopes and Anyphaena were the most abundant genera in the three groves. This study showed that soil management may influence the diversity of spiders, but the effects were weak and not consistent between years., 2_The reduction or absence of a suitable habitat for spiders under the trees in the tilled treatment might have resulted in the spiders migrating up into the canopy. However, based on the weak effects on spider abundance recorded and its potentially adverse effects on soils, tillage is not recommended for managing the incidence of pests in chestnut groves., Jacinto Benhadi-Marin ... [et al.]., and Obsahuje seznam literatury
Arbuscular mycorrhizal symbiosis is the most frequent and ancestral type of mycorrhizal symbiosis. It is estimated that at least 80% of terrestrial plant species are able to form a mutualistic relation with fungi. Consequently in the context of successful plant invasions, arbuscular mycorrhizal fungi may have a favourable if not a crucial role. The mycorrhizal status of 23 invasive species is reported here for the first time. This study also tested whether the intensity of mycorrhizal colonization of the roots of invasive species is related to that of the dominant species of invaded plant community. This is partly supported by our results when total percentages of mycorrhizal colonization were compared. In addition, the effect of habitat and community characteristics on the intensity of colonization of the roots of invasive species by arbuscular mycorrhizal fungi was tested and several significant correlations were revealed. At the among-species level, the total mycorrhizal colonization decreases and the relative arbuscular colonization increases in the roots of invasive species with increasing nitrogen availability in the habitat. Both these relations are significant after phylogenetic correction, which suggests this is an evolutionary adaptation. There are also negative correlations between the relative arbuscular colonization of invading species and the light and temperature demands of the species present in the community, and a positive correlation between the relative arbuscular colonization of the invaders and soil wetness. That all these relations are revealed at the within-species level possibly reflects differences among the habitats studied.