Changes In Soil Microbial Communities and Biomass Along a Temporal Urbanization Gradient.

Urban landscape managers increasingly recognize the critical role of soil organisms in regulating plant nutrient availability through decomposion.  Naturalized forested soils are regarded as being balanced in annual organic contributions and the microorganisms responsible for nutrient cycling.  Unfortunately, land conversion processes such as urbanization can potentially alter the ability of microorganisms to supply nutrients to plants by changing the organic additions and edaphic properties of soil.  However, because the degree of variation in the composition and structure of soil biological communities is not clear in urban areas, baseline information regarding the impact of urban land management practices on soil microbial communities is essential to improve our ability to manage urban soils and the plants they support.  This study explored soil bacterial and fungal communities along an urbanization gradient over five urban land-uses: street side terraces, new (< 5 years) residential landscapes receiving intensive management, old (> 25 years) residential landscapes receiving intensive management, old residential landscapes receiving minimal management, and rural forested lands in metropolitan Milwaukee, WI, USA.  The objectives were to assess deviations between land uses based on 1) the microbial biomass as measured by PLFA/FAME, 2) the microbial populations as measured with PLFA/FAME, and 3) the bacterial and fungal communities as measured by TRFLP.  Microbial biomass did not differ along the urbanization/land use gradient.  The measured TRFLP bacterial and fungal communities varied by land-use when assessed with multivariate (SIMPER, ANOSIM, and MDS) analysis; however the changes were not large enough to be reflected in biodiversity indices.  In addition, the microbial communities evaluated with PLFA/FAME were similar to the TRFLP communities when assessed with SIMPER, ANOSIM, and MDS, resulting in little community change in different urban land uses.  These results suggest that soil microbial communities are highly adaptive to the varying soil conditions from urbanization and landscape management.