Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Biology

Collaborative Specialization

Environment and Sustainability

Supervisor

Henry, Hugh A.L.

Abstract

Tillage can increase soil uniformity in former agricultural sites. Within plant communities, niche-based species sorting may occur among distinct soil patches (microsites), increasing diversity, and the interfaces between microsites (microedges) also may provide unique microsites. However, the influence of soil homogenization and microedges on ecosystem processes and plant responses to stress have not been examined. My thesis assessed if adding microsites containing sand, woodchips, pits or mounds increased plant species diversity, productivity, decomposition and nitrogen retention (15N tracer) and buffered plant responses to soil freezing in a tallgrass prairie restoration on former cropland. Homogenization decreased diversity in flat topsoil plots relative to topographically heterogeneous plots with pits and in the sand treatment, but increased diversity in the woodchip treatment. Homogenization reduced aboveground productivity and plant 15N retention for the woodchip treatment and increased the rate of litter decomposition. Variation in diversity and ecosystem responses were associated with effects on plant production, suggesting that the influence of soil homogenization may occur indirectly via effects on productivity. Elevated levels of plant cover and 15N retention along microedges occurred, indicating microedges may act as unique microsites and small scale ecological transition zones. Soil homogenization increased the sensitivity of total plant cover to frost stress in the sand treatment and this effect appeared to be driven by greater severity of frost stress in sand versus topsoil microsites in the heterogeneous treatment. My results indicate addition of microsites could be used to benefit plant community stability and diversity during ecological restoration.

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