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Summary

Cites transform ecosystems by changing the landscape to mesic and xeric environments, resulting in fundamental changes to soil moisture, temperature regimes, organic matter content, and nitrogen (N) inputs. However, there is little evidence of how these changes affect belowground microorganisms (e.g. bacteria and fungi) and fauna (e.g. consumers of microorganisms and their predators) in urban areas. This study seeks to a) differentiate the different groups of soil microbes and fauna, and to b) elucidate possible energy and nutrient transfers, via feeding interactions, in belowground communities from urban soils in four different sites (mesic, xeric, native, native + N). In the summer of 2011, we collected a series of 60 soil cores, split between the dry and monsoon seasons, in metro Phoenix. Soils were processed for flora and fauna, nutrient dynamic quantification, and microbial community molecular analyses. Our results indicate that mesic lawns harbor increased soil moisture over two seasons (dry and monsoon) relative to xeric and native desert sites. Furthermore, mesic soils have increased counts of fungivorous and predatory soil microarthropods. Measurements of net N nitrification and mineralization were the highest in mesic lawns, with highly variable rates in xeric sites. In addition, preliminary data show that archaea, not bacteria, dominate ammonia oxidation in the desert soils sampled here. This research will innovate urban biogeochemistry research by coupling organismal activity at different scales of the soil community with observations of N cycling patterns across a mosaic of human dominated landscapes.

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