Aboveground-belowground interactions: Investigating the role of plant communities in structuring soil bacterial communities

Abstract

Environmental heterogeneity is a traditional explanation for the biodiversity observed in nature and could be key in structuring soil microbial communities. From the soil microbe perspective, heterogeneity can be generated by both edaphic properties and by plant communities through litter inputs and root exudation. This dissertation focuses on investigating the role that plant communities play in potentially creating environmental heterogeneity within the soil and how that impacts soil bacterial community structure. Soil biota can be influenced at both local and regional scales. In Chapter 1, within a restoration context, I not only determined if plant restoration resulted in soil bacterial community restoration, I compared the relative importance of soil properties, plant communities and regional processes within an old-field and remnant prairie. I found that the capacity of the plant community to influence soil bacteria varied depending upon restoration age and land-use history. In Chapter 2, I tested the hypotheses that an increase in plant richness could promote a more diverse rhizosphere bacterial community and if any response was a result of differing plant species harboring distinct bacterial compositions (plant identity effect). Results indicated that plant identity and plant presence were more important for structuring rhizosphere bacterial communities than plant richness, potentially because not enough environmental heterogeneity was generated within the overall rhizospheres to elicit a response by the bacteria. Rhizodeposition can vary temporally in response to plant phenology, potentially influencing the detection of a plant identity effect over time. Further, rhizosphere bacterial compositions could display seasonal patterns by responding to root exudation patterns generated by plant phenology. In Chapter 3, rhizosphere bacterial communities of a forb species exhibited seasonal changes potentially associated with plant phenology, whereas those of two grass species changed over time, but not seasonally. These different temporal patterns generated conditions in which the plant identity effect of the forb was not permanent. Overall, my results show that resource heterogeneity promoted by plant communities, both spatially and temporally, can be an important, but not exclusive component, in shaping soil bacterial communities. Further, the influence of the plant community can vary depending upon species, plant phenology, and community composition.