Effects of elevated carbon dioxide on soil microbial communities of the Mojave Desert

The objective of this study is to determine soil microbial community structure in the framework of increased atmospheric carbon availability associated with global change. Since arid ecosystems make up a considerable fraction of our biosphere, their response to global change will be of significance. Further, implication for plant and ecosystems productivity in arid environments may be linked to changes in diversity among microbial communities, since the cycling of essential elements in the soil is often mediated by microbes. The following are three sets of experiments designed to examine the changes in microbial diversity associated with a global change factor, an increase in atmospheric carbon dioxide (CO2); To start the examination of the differences caused by elevated atmospheric CO2, bacterial communities living in soil associated with Larrea tridentata, a dominant Mojave Desert shrub, were studied. Terminal restriction length polymorphism (T-RFLP) analysis, and preliminary phylogenetic analysis, of 16S rDNA amplified from soil indicated that there is an alteration in the soil bacterial community structure between ambient and elevated CO2 conditions. Preliminary richness estimation indicated that the studied environments have been greatly undersampled. The analysis also revealed T-RFLP may not be a suitable method to study the microbial diversity in the studied environment, and more extensive 16S rDNA sampling is necessary to determine the effects of elevated atmospheric CO2 on the diversity of soil microbes in an intact desert environment; The effects of elevated CO2 on soil microbial communities were further tested through microbial community surveys by the construction of larger environmental gene libraries to identify the dominant operational taxonomic units (phylotypes) among bacterial and fungal communities. To better understand how community composition relates to environmental changes, a multifaceted approach consisting of qualitative and quantitative methods to assess community diversity was employed to characterize the microbial communities found in the different CO2 treatments. Significant changes in the bacterial and fungal community structures in enriched CO2 conditions were observed; The final experiments used to determine the structure of microbial communities relied on the quantitation of total and specific groups of bacteria. Quantitative polymerase chain reaction (QPCR) using TaqMane technology was employed to infer population density of total and Gram-positive bacteria in rhizosphere soil DNA exposed to enhanced and ambient CO2. The QPCR results indicate that the density of bacteria is similar in the two CO 2 treatments, while Gram-positive microorganisms decreased by 44% in ambient relative to those observed in enriched CO2 conditions. These experiments also suggest that a cumulative change in many fungal phyla was observed in conditions of elevated CO2, while change among bacteria was group-specific