Life Beneath the City: The Effects of Urbanization on Soil Microbial Community Composition.

By 2030, the area of urbanized land is expected to expand globally by 200% as compared to its area in 2000. As urban landscapes often replace functionally important ecosystems, it is important to understand how urbanization alters ecosystem function, and the drivers of those changes. Soil microbial communities mediate nitrogen and carbon transformations (particularly storage in soils), and are therefore of great significance to the implementation of nutrient management plans and are of global importance as we pursue carbon capture and sequestration strategies. We performed a microbial community analysis and function assay in five cities (Helsinki and Lahti, Finland; Baltimore, USA; Budapest, Hungary; Potchefstroom, South Africa). In each city, four habitat categories were chosen from the urban disturbance/management gradient: reference ecosystem (outside the city), remnant ecosystem (within the city), managed lawn, and a highly disturbed ruderal habitat. Microbial community data are supplemented with physical and chemical characteristics of the soil, a standardized decomposition assay, and earthworm assay. A preliminary three-dimension NMS ordination clustered sites by city (P<0.001) and by site category within each city (P<0.001). Baltimore separated completely, while the remaining cities overlapped to various degrees indicating greater microbial community similarity. Pearson correlations show that SOM correlates significantly with axis 1 (P<0.01) and axis 2 (P<0.00001), and that pH correlates with both axes (P<0.00001 for each). Neither pH nor SOM correlate significantly with axis 3. This preliminary evidence suggests that microbial communities across cities respond to the higher pH and lower SOM found in the more disturbed sites. Future research will incorporate nutrient status, texture, and geographic distance into the statistical model.