Effects of fertilization and haying on soil bacterial communities in a northeastern Kansas experiment

Managed grasslands composed of introduced C₃ grasses now dominate large areas of eastern Kansas that were once occupied by native tall-grass prairie. In 2000 we established a long-term field experiment to evaluate the interactive effects of cool-season grassland management (fertilization and haying) on plant productivity, soil processes and plant community structure. In 2003 we found that vegetative production was increased significantly by fertilization, but to the greatest extent in hayed plots. Plant diversity was significantly reduced by fertilization, but only in the absence of haying. Because (1) fertilization and haying interact strongly to impact plant communities and ecosystem attributes, and (2) changes in plant communities can lead to changes in the soil microbial community, we wanted to assess the soil bacterial community within this experimental context. In early June 2004, bulk soil was sampled, homogenized and analyzed via terminal restriction fragment length polymorphism (T-RFLP). The total bacterial community and dinitrogen fixing bacterial communities were examined by amplifying the 16S rRNA and the nifH genes, respectively. Ordination analyses did not indicate treatment differences in composition of either the total or the nifH bacterial communities. When investigating the relative operational taxonomic unit (OTU) richness and diversity, it was found that mowing significantly increased OTU richness and OTU diversity of the total bacterial community. However, no significant differences were found when examining the dinitrogen fixing bacterial community.