, Volume 12, Issue 4, pp 654-671
Date: 05 May 2009

Urbanization Alters Soil Microbial Functioning in the Sonoran Desert

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Cities can transform ecosystems in multiple ways, through modification of land use and land cover and through exposure to altered physical, chemical, and biological conditions characteristic of urban environments. We compared the multiple impacts of urbanization on microbial carbon (C) and nutrient cycling in ecosystems across Phoenix, Arizona, one of the fastest growing metropolitan areas in the USA. Land-use/land-cover change from desert to managed ecosystems altered soil microbial functioning, primarily through changes in organic matter supply. Although residential xeriscapes often feature native plants and patchy structure like deserts, spatial heterogeneity in soil biogeochemical cycling was not tightly linked to plant canopies. Grassy lawns exhibited higher nitrogen (N) and phosphorus demand by microorganisms than other landscape types, suggesting that high C quality may effectively sequester these nutrients during periods between fertilization events. Soils in native desert remnants exposed to the urban environment had higher organic matter content, but supported lower activities of extracellular peroxidase enzymes compared to outlying deserts. Experimental N enrichment of desert systems decreased peroxidase activities to a similar extent, suggesting that protected desert remnants within the city are receiving elevated N loads that are altering biogeochemical functioning. Although some microbial processes were spatially homogenized in urban desert remnants, resource islands associated with plants remain the dominant organizing factor for most soil properties. The extent to which native desert preserves within the city functionally resemble managed xeriscapes and lawns suggests that these remnant ecosystems are being ‘domesticated’ by exposure to the urban environment.

Author Contributions

This work was a collaborative effort. S.J. Hall, R.A. Sponseller, R. Davies, and N.B. Grimm conceived of the project and collectively mentored NSF REU students P. Ortiz and B. Ahmed. S.J. Hall helped to secure the primary NSF grant and supplemental REU funding, analyzed the data, and wrote the manuscript; B. Ahmed and P. Ortiz (NSF REU students) performed all field work and laboratory analyses; R. Davies and R.A. Sponseller helped to identify research sites and guided laboratory and field work; R.A. Sponseller also edited the manuscript and provided insight and feedback throughout the project; N.B. Grimm helped to secure the primary NSF grant and supplemental REU funding, edited the manuscript, and was the primary advisor for B. Ahmed’s undergraduate honors thesis.