66 Turnquist et al.: An Examination of Soil Microbial Communities and Litter Decomposition In general, variations to microbial communities appear to be more pronounced when urbanization occurs in native landscapes, where primary produc- tion is severely limited by extremes in temperature and moisture (Xu et al. 2014). Native limitations to primary production and plant communities are oſten overcome during the creation and manage- ment of urbanized landscapes through irrigation and fertilization; thereby stimulating a buildup of soil carbon that largely differs from the native landscape. The size and quality of the soil carbon pool, in particular, has been shown to influence both microbial biomass and ecosystem function- ing, particularly nitrogen mineralization (Kaye et al. 2005). Kaye et al. (2005) detected limited dif- ferences in soil microbial assemblages attributed to the increased urbanization; however, they addition- ally observed statistically higher microbial biomass in urban landscapes relative to the surrounding agricultural areas. They attributed this increase in microbial biomass to elevated soil carbon storage and enhanced carbon cycling rates in the urban landscape as compared to agricultural sites. Con- trary to Kaye et al. (2005), the present study found no changes in soil microbial biomass or total carbon across the different land uses; therefore, it would appear the statistical differences observed in SOM are not of sufficient magnitude to generate a signifi- cant difference in soil carbon or large scale shiſts in the microbial composition, and likely did not limit the growth of the microbial community. Within the land-use categories with the highest levels of urbanization in this study, the soil carbon pools and accompanying chemical and physical envi- ronments are capable of supporting a high level of microbial diversity and potentially, associated ecological functioning; as verified by statistically similar outcomes of in situ litter decomposition. Despite being a coarse measure of microbial activity, the comparable degradation of a moderately difficult to decompose organic substrate (Quercus alba leaves) suggests the biological communities in the different urban areas have a comparable capac- ity to decompose organic material. Although bulk densities were elevated in the highly urbanized soils, any oxygen deficiencies associated with high bulk densities did not limit microbial activity in the deg- radation of the transposed leaf litter; this indicated the presence of a potentially resilient microbial ©2016 International Society of Arboriculture assemblage. Furthermore, using the forested land use as a model for a sustainably functioning soil, the similarity in litter decomposition suggests the microbial communities in the different Milwaukee landscapes is similar in activity to that of the area forests. Therefore, because there were no differences in the observed microbial activity and biomass, and only subtle changes in the microbial communities, it is reasonable to conclude that the microbial composition and activity was ubiquitous in the Milwaukee area sites encompassed by this study. CONCLUSION This study was unable to detect large scale, consistent differences in bacterial or fungal community struc- ture and microbial biomass along an urbanization gradient, despite using a variety of well-documented and optimized procedures. Although subtle variances in microbial community profiles were observed within the urbanized landscapes, the microbial communities were largely redundant. Any signifi- cant differences observed in soil properties did not reflect large scale differences in microbial composi- tion or biomass, which is likely attributed to the high levels of soil organic matter and carbon resources throughout the locations encompassed in this study. Therefore, because these soils appear to have the capacity to decompose organic matter equally within a similar geographic and climatic region, the impact of urbanization and landscape management practices does not appear to dramatically alter soil micro- biology where parent material, soil-forming pro- cesses, and soil carbon resources are homogeneous. LITERATURE CITED Anderson, I.C., and J.W.G. Cairney. 2004. Diversity and ecology of soil fungal communities increased understanding through the application of molecular techniques. Environmental Microbiol- ogy 6(8):769–779. Ayansina, A.D., and B.A. Oso. 2006. Effect of two commonly used herbicides on soil microflora at two different concentrations. African Journal of Biotechnology 5(2):129–132. Balser, T.C. 2001. The impact of long-term nitrogen addition on microbial community composition in three Hawaiian forest soils. The Scientific World 1(2):500–504. Blake, G.R., and K.H. Hartage. 1986. Bulk Density. pp. 363–375. In: A. Klute (Ed.). Methods of Soil Analysis. Part 1, second edition. Agronomy Monograph 9. ASA and SSSA, Madison, Wisconsin, U.S. Clarke, K.R., and R.M. Warwick. 2001. Changes in Marine Com- munities: An Approach to Statistical Analysis and Interpreta- tion, second edition. PRIMER-E Ltd, Plymouth, UK.
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