Publication Date

Spring 2011

Degree Type


Degree Name

Master of Science (MS)


Biological Sciences


Sabine Rech


archaea, bacteria, desert, diversity, precipitation transect, soil community

Subject Areas

Microbiology; Environmental Sciences; Soil Sciences


Deserts occupy one third of the total land mass of Earth, yet little is known about microbial soil communities under conditions of low precipitation and humidity. The Mojave Desert of the Southwestern United States provides an opportunity to observe microbial communities along a precipitation transect. The diversity of these communities can elucidate which specific groups of Eubacteria and Archaea are best adapted to limited liquid water.

Two methods were utilized to determine patterns and trends of the microbial soil communities under varying precipitation levels. Viable plate counts allowed comparison of culturable microorganisms over a four-year period. Molecular techniques distinguished unculturable Eubacteria from Archaea. The results indicated three trends. First, the number of culturable microbes decreased from 10⁷ to 10⁶ CFUs/g dry soil as the annual precipitation decreased. Also, the diversity of the eubacterial communities increased as the annual precipitation decreased, indicated by Shannon-Wiener indices increasing from 3.51 to 3.76. Finally, the diversity increases for archaeal communities were small, producing Shannon-Wiener indices from 1.21 to 1.36. Possible indicator bacteria for desertification processes were suggested by the increasing numbers and diversity of cyanobacteria at the drier sample sites.