An investigation of plant and soil microbial community homogenization in urban parklands

Caleb T. Lumsden and Emily S. J. Rauschert, Biological, Geological and Environmental Sciences, Cleveland State University, Cleveland, OH, Sarah R. Carrino-Kyker and David J. Burke, The Holden Arboretum, Kirtland, OH

Background/Question/Methods
Biological communities across the world are becoming more similar to each other, a phenomenon termed biotic homogenization. Urbanization is a major driver of homogenization, and the relationship between these processes has been observed at global and local scales. Intuitively, biological communities directly impacted by urban development are expected to experience compositional change; however, homogenization has also been observed in proximal natural areas. While these areas play an important role in conservation efforts, few studies have quantified the relationship between urbanization and floral community homogenization in such areas, and even fewer have documented this relationship in soil microbial communities. Thus, the purpose of this study was to assess the degree of homogenization in plant and microbial communities in parklands on an urban-rural gradient in the Cleveland Metropolitan area. We selected 11 sites throughout the Cleveland Metroparks and categorized them into urban, suburban, and exurban sites based on their proximity to the urban core. From these sites, we analyzed above-ground plant community data provided by the Cleveland Metroparks by quantifying α (site richness) and β (species turnover) diversity, as well as the seedbank community by obtaining and germinating soil cores from each focal site. Soil microbial communities were characterized using terminal restriction fragment length polymorphism (TRFLP) analysis. We hypothesized that urban sites would exhibit less floral and microbial β diversity than rural sites, with intermediate levels in suburban sites, and that the increase in native floral α diversity (∆α) between 2013 and 2018 surveys would be greater in exurban sites relative to urban sites.
Results/Conclusions
Plant community data analysis indicated that spatial turnover was significantly greater in exurban sites than in urban sites (F2,8 = 5.18, P = 0.036). Additionally, the mean increase in native plant richness over a five-year period was significantly greater in exurban sites relative to suburban sites (P = 0.032), indicating that the rate at which parklands gain native species may be affected by urbanization. Preliminary analyses indicated that bacterial communities were not significantly different by urban intensity, nor were fungal communities. However, both microbial communities were significantly different by site (F2,48 = 3.4524, P=.002427; F2,50 = 2.4186, P=.028), indicating that microbial communities are likely influenced by factors other than urbanization. Our findings suggest that plant and microbial communities respond differentially to urbanization; while plant communities seem to be homogenized by urbanization, microbial communities may be responding more to finer scale differences between sites.