Differences in eubacterial and archaeal soil communities along a precipitation transect in the Mojave Desert

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.