The Effect of Four Early-Successional Pennsylvania Tree Species on Soil Bacterial Communities SMITH, G. and K. KLEINER, Dept. of Biological Sciences, York College of Pennsylvania, York, PA USA ABSTRACT The role of microbial communities on the above ground plant species composition has been well documented. However, little research has been done on the effect of plants on the microbial community below ground, particularly bacterial communities. Previous work has been conducted in the field, therefore preventing the comparison of each plant species’ microbial community. To examine only the effects of a specific tree on the bacterial community, trees were planted in separate pots with autoclaved soil (2:2:1, soil, peat, perlite). The trees used were Yellow Polar (Liriodendron tulipifera), Black Locust (Robinia pseudoacacia), Tree of Heaven (Ailanthus altissima), and Red Maple (Acer rubrum). Soil extracts were used to inoculate gram negative and ecolog microtiter plates and agar plates. Black Locust and Ailanthus had significantly greater functional diversity and functional richness when compared to the control. Yellow Poplar’s bacterial community strongly resembled the control pot’s bacterial community. Heterotrophic counts corroborated with the results from the gram negative and ecolog microtiter plates. INTRODUCTION Species diversity in plant communities was originally thought to be influenced by competition and abiotic resources. However, it has been shown that the soil microbial community also affects the diversity and growth of above ground plant species (Bever 1994; Bever et al. 1997). The plant community in turn has an effect on the microbial community it supports (Bever et al. 1997). Previous studies have only examined the fungal aspect of the microbial communities. These studies show that most land plant’s roots are associated with different mycorrhizal fungi (Read 1998). Little research has been done on the bacterial community and how different tree species affect them. Research done was completed in the field where interspecific competition, intraspecific competition, herbivory, and abiotic factors may vary from plant to plant. Our hypothesis was: Plants have been shown to support different fungal communities. Therefore, there should also be a difference in the bacterial community each tree supports when compared to the control. METHODS  Tree of Heaven, Black Locust, and Red Maple were germinated from seed and Yellow Poplar was collected from an area near Wellsville, Pa.  Roots were sterilized with 1.05% sodium hypochlorite solution and planted in soil mixture of 2:2:1 mixture of peat moss, autoclaved soil, and sterile perlite, respectively.  Black Locust seedlings were inoculated with Rhizobium.  Soil was extracted from around the roots and diluted with PBS.  Average well color development was calculated using Biolog Ecolog, and Gram negative microtiter plates (Garland and Mills 1991).  Functional diversity, functional evenness, and functional richness were calculated from these readings (Zak et al. 1994) and each tree species was compared to the control after one-way ANOVA (Prism software).  Using same PBS and soil mixture, Heterotrophic counts were conducted using the pour plate method. RESULTS  Functional diversity was greater for black locust and Ailanthus as compared to control (P < 0.05; figure 1 and figure 2).  Functional richness was greater for black locust and Ailanthus as compared to control (P < 0.05; figure 5 and figure 6).  Functional evenness differed among tree species for gram negative plates only (P < 0.02; figure 3).  Heterotrophic counts of bacteria did not differ among tree species (P < 0.10; figure 7). DISCUSSION The hypothesis that each tree species supports different bacterial communities when compared to the control was supported in the cases of Ailanthus and Black Locust using the Biolog microplates. Red Maple and Yellow Poplar’s bacterial communities were not significantly different from the control’s bacterial community.  Species diversity is a function of a population’s richness and evenness. Therefore, Ailanthus and Black Locust’s functional diversity is being driven by their functional richness and not their functional evenness.  Heterotrophic counts corroborated with functional diversity  While this research did provide evidence for different bacterial communities for Ailanthus and Black Locust, there are some limitations to these results 1.The bacterial communities found are not necessarily the communities that would be found under natural conditions. 2.Not all bacteria can be cultured, so some bacteria may have been present and not accounted for. LITERATURE CITED Bever, James D Feedback between plants and their soil communities in an old field community. Ecology. 75: Bever, J.D., K.M. Westover, J. Antonovics Incorporating the soil community into plant population dynamics:the utility of the feedback approach. The Journal of Ecology. Vol. 85, no 5: Garland J. and A. Mills Classification and characterization of heterotrophic microbial communities on the basis of patterns of community-level sole-carbon-source utilization. Applied and Environmental Microbiology 57: Read, D Plants on the web. Nature 396: Zak,J.C., M.R. Willig, D.L. Moorhead, H.G. Wildman Functional diversity of microbial communities: a quantitative approach. Soil Biology and Biochemistry. Vol. 26 no. 9: ACKNOWLEDGEMENTS Thanks to Dr. Carolyn Mathur PhD, for her time and assistance in with Heterotrophic plate counts. Figure 1 Figure 2 Figure 3Figure 4 Figures 1-6- mean and 95% confidence interval used; n=4; * indicates different from the control X-axis legend C. - Control Y.P. - Yellow Poplar R.M. - Red Maple B.L. - Black Locust T.O.H. - Ailanthus Figure 5 Figure 6 Figure 7 DATA ANALYSIS  Kruskal-Wallis test  Post test: treatment compared to the control Dunn’s Multiple Comparison test used