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Quantitative analysis of soil microbial diversity in the hyperarid Atacama Desert, Chile

Drees, Kevin Paul

Titre  : Quantitative analysis of soil microbial diversity in the hyperarid Atacama Desert, Chile

Auteur  : Drees, Kevin Paul

Université de soutenance : THE UNIVERSITY OF ARIZONA

Grade :Doctor of Philosophy (PhD) 2004

The Atacama Desert of northern Chile is one of the most arid regions on Earth. The central plateau, between the coastal escarpment and the Andes, is devoid of vegetation and receives only millimeters of rain every few years. Though plants are absent in the soils of this desert, perhaps bacteria can survive, and even thrive, in these hyperarid conditions. This dissertation represents the first comprehensive study of bacterial diversity in the driest central latitudes (approximately 24°S) of the Atacama Desert. Study 1 covers the development of a soil DNA extraction method for the study of soil bacterial populations. This method was field tested in an ecology study in the Santa Catalina Mountains of southern Arizona. In Study 2, Atacama soils were sampled in two transects at approximately 24°S and 25°S. The first transect runs across the absolute (plantless) desert and through several narrow bands of sparse vegetation at high altitudes in the Andes. The second transect is within the well-developed fog zone near Paposo on the Pacific coastal escarpment, where an endemic plant community called lomas is established. Analysis of DGGE profiles of bacterial !6S rRNA genes extracted from these soils with Kruskal’s Isotonic Multidimensional Scaling indicates that the bacterial populations cluster into several groups, including the low diversity populations of the core absolute desert, and the higher diversity high elevation Andean populations influenced by the vegetation of Andean biomes. Only one group clustered in the lomas ; the rest of the profiles were unique, demonstrating the high diversity of bacterial populations within this diverse vegetation community. Soil 3107, which is within the absolute desert, clustered with the Andean bacterial populations. This soil lies within the transition zone between the low precipitation of the absolute desert (approximately 2.4 mm per year) and the higher precipitation of the high elevation Andes (approximately 47.1 mm per year). This Andean bacterial population may extend further into the absolute desert than the Andean vascular plants due to superior aridity tolerance. Alternatively, this bacterial population may be a relic from when the Andean vegetation advanced through this elevation in a wet period 3000 years ago.



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