Background/Question/Methods Nitrogen is a limiting element for life on earth and this is more so in arid and semi-arid environments, and more importantly, this cycle is well understood molecularly and is regulated mostly by microorganisms. As arid environments expand due to global change, the assessment of the role of desiccation in changing microbial diversity and functional groups is important to understand possible changes in biogeochemical cycles. The nifH phylotypes among habitats show characteristic distribution patterns of N-fixing organisms. The functional equivalence of nirS and nirK in denitrifying organism is not reflected in their ecological distribution, but at local-scale, an arid zone with high salinity, and extreme oligotrophic conditions could reveal patterns that have been conceal by higher organic material, as could be in the majority of the habitats analyzed. For that we analyzed the taxonomical, nifH, nirK and nirS diversity of two soils with contrasting levels of humidity in the Cuatro Cienegas basin of Coahuila, Mexico.We constructed 16s rRNA clone libraries for general taxonomic and community descriptions and analyzed nifH, nirK and nirS clone libraries for functional group assessment. Biogeochemical analyses were performed for each type of soil at different times during one year.
Results/Conclusions Differences in taxonomical composition were observed among soils. The more humid soil showed greater bacterial diversity and nutrient concentration than the drier soil. The greatest functional differences were observed within the denitrifying bacterial guild, while nitrogen fixers shared more taxonomic groups between sites. Our results suggest that differences in bacterial community composition and diversity are produced by nutrient availability, that in turn is caused by water availability. This supports the idea of moisture-limited taxonomic and functional diversity, remarking the relevance of the decrease moisture in the soils.